Electronic Tutorials

2010-06-26T02:37:00.000-07:00

ELECTRONIC TUTORIAL AND ARTICLE

(Electronic theory and atom)

Atoms and electrons

Everybody knows about atoms and electrons don't they? Well we could skip this part but of course we won't because you will likely learn something new.

Electron theory states all matter is comprised of molecules, which in turn are comprised of atoms, which are again comprised of protons, neutrons and electrons. A molecule is the smallest part of matter which can exist by itself and contains one or more atoms.

If you turn on a light switch for example you will see the light bulb (globe) glow and emit light into the room. So what caused this to happen? How does energy travel through copper wires to light the bulb? How does energy travel through space? What makes a motor turn, a radio play?

To understand these processes requires an understanding of the basic principles. For the light to glow requires energy to find a path through the light switch, through the copper wire and this movement is called electron flow. It is also called current flow in electronics. This is the first important principle to understand.

The word matter includes almost everything. It includes copper, wood, water, air....virtually everything. If we were able to take a piece of matter such as a drop of water, divided it by two and kept dividing by two until it couldn't be divided any further whileit was still water we would eventually have a molecule of water.

A molecule, the smallest particle which can exist, of water comprises two atoms of Hydrogen and one atom of Oxygen - H₂O.

An atom is also divisible - into protons and electrons. Both are electrical particles and neither is divisible. Electrons are the smallest and lightest and are said to be negatively charged. Protons on the other hand are about 1800 times the mass of electrons and are positively charged. Each are thought to have lines of forces (electric fields) surrounding them. In theory, negative lines of force will not join other negative lines of force. In fact they tend to repel each other. Similarly positive lines of force act in the same way.

The fact that electrons repel electrons and protons repel protons, but electrons and protons attract one another follows the basic law of physics:

Like forces repel and unlike forces attract.

Sounds a bit like a teenage romance - opposites attract.

When an electron and proton are brought in close proximity to one another it is the electron which moves because the proton is 1800 times heavier. It is the electron which moves in electricity. Even though the electron is much smaller, its field is quite strong negatively and is equal to the positive field of the proton.

If the field strength around an electron at a distance of 1,000,000th of a centimetre was a certain amount, then the field strength around an electron at a distance of 2,000,000th of a centimetre will be 1/4 as much. This is because the field decreases inversely with the distance squared. If an increase in one thing causes an increase in something else, these two things are said to vary directly. 2,000,000 electrons on an object produce twice the negative charge than 1,000,000 electrons would.

Since the electric-field strength of an electron varies inversely with the distance squared, the field strength a centimetre away would be quite weak. The fields surrounding protons and electrons are known as electrostatic fields. "Static" means stationary or not moving.

When electrons are made to move, the result is dynamic electricity. "Dynamic" means movement. To produce a movement of an electron it is necessary to either have a negatively charged field "push it", a positively charged field "pull it", or, as normally occurs in an electric circuit, a negative and positive charge (a pushing and pulling of forces).

There are more than one hundred different atoms or elements. The simplest and lightest is Hydrogen. An atom of Hydrogen consists of one electron whirling around one proton much like the moon revolving around the earth. The next atom in terms of weight is Helium (He) consisting two protons and two electrons. The third atom is Lithium (Li) with three protons and three electrons and so it goes on.

Some of the elements and their atomic weights are:

Hydrogen (1); Helium (2); Lithium (3); Carbon (6); Oxygen (8); Aluminium (13); Silicon (14); Iron (26); Nickel (28); Copper (29); Germanium (32); Gold (79); Lead (82).

Most atoms have a nucleus consisting of all the protons of the atom and also one or more neutrons. The remainder of the electrons (always equal in number to the nuclear protons) are whirling around the nucleus in different layers. The first layer of electrons outside the nucleus can only accomodate two electrons. If the atom has three electrons then two will be in the first layer and the third will be in the next layer. The second layer is completely filled when eight electrons are whirling around it. The third is filled when eighteen electrons are whirling around.

Don't think these electrons whirl around in some haphazard manner, they don't. The electrons in an element of a large atomic number are grouped into rings having a definite number of electrons. The only atoms in which these rings are completely filled are those of inert gaseous elements such as Helium, Neon, Argon, Krypton, Xenon and Radon.

All the other elements have one or more uncompleted rings of electrons.

Some of the electrons in the outer orbit of atoms such as copper or silver can be easily dislodged. These electrons travel out into the wide open spaces between the atoms and molecules and may be termed free electrons. It is the ability of these electrons to drift from atom to atom which makes electric current possible. Other electrons will resist dislodgement and are called bound electrons.

Electron Theory and Metals

It would be impossible for electronics to exist without metals and they are crucial to modern technology. Here are some of the properties of a few metals commonly used in electronics.

Figure 1. - properties of selected metals

Note: Iron is the only metal significantly affected by a magnet.

1. Density at 20^° C is Kg per M³

2. Ohms ^-1

3. These properties can be altered dramatically by the presence of relatively small amounts of impurities.

Another property of metals is malleability. This is because rows of positive ions can easiy slide over one another and still maintain a regular pattern. This is the reason why metals can be stretched without breaking.

Alloys

Most metals in use today are in fact alloys. Common examples are stainless steel, high speed steel from which our drill bits are made and in common use in electronics - Solder (60% Sn, 40% Pb - that's tin and lead) and; Nichrome for resistance wire and electrical heating elements (80% Ni, 20% Cr - that's nickel and chrome).

source: http://www.electronics-tutorials.com/basics/electron-theory.htm

Decoder/Demultiplexer

2010-06-08T23:21:00.000-07:00

The 1-to-2 Line Decoder/Demultiplexer

The opposite of the multipalexer circuit, logically enough, is the demultiplexer. This circuit takes a single data input and one or more address inputs, and selects which of multiple outputs will receive the input signal. The same circuit can also be used as a decoder, by using the address inputs as a binary number and producing an output signal on the single output that matches the binary address input. In this application, the data input line functions as a circuit enabler — if the circuit is disabled, no output will show activity regardless of the binary input number.

A one-line to two-line decoder/demultiplexer is shown below.

This circuit uses the same AND gates and the same addressing scheme as the two-input multiplexer₀ and the X1 input would reach only OUT₁. circuit shown in these pages. The basic difference is that it is the inputs that are combined and the outputs that are separate. By making this change, we get a circuit that is the inverse of the two-input multiplexer. If you were to construct both circuits on a single breadboard, connect the multiplexer output to the data IN of the demultiplexer, and drive the (A)ddress inputs of both circuits with the same signal, you would find that the initial X0 input would be transmitted to OUT

The one problem with this arrangement is that one of the two outputs will be inactive while the other is active. To retain the output signal, we need to add a latch circuit that can follow the data signal while it's active, but will hold the last signal state while the other data signal is active. An excellent circuit for this is the D (or Data) Latch. By placing a latch after each output and using the Addressing input (or its inverse) to control them, we can maintain both output signals at all times. If the Address input changes much more rapidly than the data inputs, the output signals will match the inputs faithfully.

Like multiplexers, demultiplexers are not limited to two data signals. If we use two addressing inputs, we can demultiplex up to four data signals. With three addressing inputs, we can demultiplex eight signals. The demonstration of the 2-to-4 line decoder/demultiplexer is much smaller than the demo for the four-input multiplexer, because it has fewer independent input signals. With one data input and two addressing inputs, the decoder/demultiplexer only needs 8 images for the full demonstration.

The 2-to-4 Line Decoder/Demultiplexer

Like the multiplexer circuit, the decoder/demultiplexer is not limited to a single address line, and therefore can have more than two outputs. With two, three, or four addressing lines, this circuit can decode a two, three, or four-bit binary number, or can demultiplex up to four, eight, or sixteen time-multiplexed signals.

A 2-to-4 line decoder/demultiplexer is shown below.

source : http://www.play-hookey.com

As a decoder, this circuit takes an n-bit binary number and produces an output on one of 2ⁿ output lines. It is therefore commonly defined by the number of addressing input lines and the number of data output lines. Typical decoder/demultiplexer ICs might contain two 2-to-4 line circuits, a 3-to-8 line circuit, or a 4-to-16 line circuit. One exception to the binary nature of this circuit is the 4-to-10 line decoder/demultiplexer, which is intended to convert a BCD (Binary Coded Decimal) input to an output in the 0-9 range.

If you use this circuit as a demultiplexer, you may want to add data latches at the outputs to retain each signal while the others are being transmitted. However, this does not apply when you are using this circuit as a decoder — then you will want only a single active output to match the input

Priority Encoder

2010-06-08T23:09:00.000-07:00

Priority Encoder (4:2 bits)

Circuit Description

A 4-bit priority encoder (also sometimes called a priority decoder). This circuit basically converts the 4-bit input into a binary representation. If the input n is active, all lower inputs (n-1 .. 0) are ignored:

x3 x2 x1 x0  y1 y0
------------------
1  X  X  X   1  1
0  1  X  X   1  0
0  0  1  X   0  1
0  0  0  X   0  0

The circuit operation is simple. Each output is driven by an OR-gate which is connected to the NAND-INV outputs of the corresponding input lines. The NAND gate of each stages receives its input bit, as well as the NAND gate outputs of all higher priority stages. This structure implies that an active input on stage n effectively disables all lower stages n-1 .. 0.

Note that the circuit function as specified here does not depend at all on the least significand input bit.

A common use of priority encoders is for interrupt controllers, to select the most critical out of multiple interrupt requests. Due to electrical reasons (open collector outputs), priority encoders with active-low inputs are also often used in practice.

Priority Encoder (8:3 bits)

Circuit Description

An 8-bit priority encoder. This circuit basically converts a one-hot encoding into a binary representation. If input n is active, all lower inputs (n-1 .. 0) are ignored. Please read the description of the 4:2 encoder for an explanation.

x7 x6 x5 x4 x3 x2 x1 x0   y2 y1 y0
----------------------------------
1  X  X  X  X  X  X  X    1  1  1
0  1  X  X  X  X  X  X    1  1  0
0  0  1  X  X  X  X  X    1  0  1
0  0  0  1  X  X  X  X    1  0  0
0  0  0  0  1  X  X  X    0  1  1
0  0  0  0  0  1  X  X    0  1  0
0  0  0  0  0  0  1  X    0  0  1
0  0  0  0  0  0  0  X    0  0  0


source : http://tams-www.informatik.uni-hamburg.de

T flip flop

2010-06-08T23:07:00.002-07:00

This type of flip-flop is a simplified version of the JK flip-flop. It is not usually found as an IC chip by itself, but is used in many kinds of circuits, especially counter and dividers. Its only function is that it toggles itself with every clock pulse (on either the leading edge, on the trailing edge) it can be constructed from the RS flip-flop as shown in Figure 2.10 (a).

**Figure 2.10:** The T flip flop

This flip flop is normally set, or ``loaded'' with the preset and clear inputs. It can be used to obtain an output pulse train with a frequency of half that of the clock pulse train, as seen from the timing diagram, Figure 2.10 (b). In this example, the T flip flop is triggered on the falling edge of the clock pulse.

Several T flip-flops are often connected together in a simple IC to form a ``divide by N'' counter, where N is usually 5, 10, 12 or a power of 2.

source : http://web.cs.mun.ca/~paul/cs3724/material/web/notes/node15.html

The D Latch and the D flip-flop

2010-06-08T23:07:00.001-07:00

It is possible to create a latch which has no race condition, simply by providing only one input to a RS latch, and generating an inverted signal to present to the other terminal of the latch. In this case, the S and R inputs are always inverted with respect to each other, and no race condition can occur. The circuit for a D latch is shown in Figure 2.7.

**Figure 2.7:**

The D latch is used to capture, or ``latch'' the logic level which is present on the Data line when the clock input is high. If the data on the line changes state while the clock pulse is high, then the output, , follows the input, . This effect can be seen in the timing diagram, Figure 2.8 (a).

The D flip-flop, while a slightly more complicated circuit, performs a function very similar to the D latch. In the case of the D flip-flop, however, the rising edge of the clock pulse is used to ``capture'' the input to the flip flop. This device is very useful when it is necessary to ``capture'' a logic level on a line which is very rapidly varying. Figure 2.8 (b) shows a timing diagram for a D-type flip-flop. This type of device is said to be ``edge triggered'' -- either rising edge triggered (i.e. a 0-1 transition) or falling edge triggered (i.e., a 1-0 transition) devices are available.

**Figure 2.8:**

Both the D latch and D flip-flop have the following truth table:

		Clock	D	Q
0	1	x	x	1	0
1	0	x	x	0	1
0	0	x	x	1	1
1	1	or 1	0	0	1
1	1	or 1	1	1	0
1	1	0	X

The symbol means a leading edge, or transition as the clock input to the flip flop. For a D latch, it would be the level 1.

source : http://web.cs.mun.ca/~paul/cs3724/material/web/notes/node13.html

SR Bistable Switch Debounce Circuit

2010-06-08T23:04:00.000-07:00

Switch Debounce Circuits

One practical use of this type of Set-Reset circuit is as a latch used to help eliminate mechanical switch "Bounce". As its name implies, switch bounce occurs when the contacts of any mechanically operated Switch, Push-button or Keypad is operated and the internal switch contacts do not fully close cleanly, but bounce together first before closing (or opening) when the switch is pressed. This gives rise to a series of pulses as long as tens of milliseconds that an electronic system or circuit such as a digital counter may see as a series of logic pulses instead of one long single pulse and behave incorrectly, for example, it may register multiple counts instead of a single count. Then Set-Reset SR Flip-flops or Bistable Latch circuits can be used to eliminate this problem and this is shown below.

SR Bistable Switch Debounce Circuit

Depending upon the current state of the output, if the Set or Reset buttons are depressed the output will change over in the manner described above and any additional unwanted inputs (bounces) from the mechanical action of the switch will have no effect on the output. When the other button is pressed, the very first contact will cause the latch to change state, but any additional bounces will also have no effect. The SR flip-flop can then be RESET automatically after a short period of time, for example 0.5 seconds, so as to register any additional and intentional repeat inputs from the same switch contacts, for example multiple inputs from the RETURN key.

Commonly available IC's specifically made to overcome the problem of switch bounce are the MAX6816, single input, MAX6817, dual input and the MAX6818 octal input switch debouncer IC's. These chips contain the necessary flip-flop circuitry to provide clean interfacing of mechanical switches to digital systems.

Set-Reset Latches can also be used as Monostable (one-shot) pulse generators to generate a single output pulse, either High or Low, of some specified width or time period for timing or control purposes. The 74LS279 is a Quad SR Bistable Latch IC, which contains 4 individual NAND type bistable's within a single chip enabling switch debounce or monostable/astable clock circuits to be easily constructed.

Gated or Clocked SR Flip-Flop

It is sometimes desirable in sequential logic circuits to have a bistable SR flip-flop that only change state when certain conditions are met regardless of the condition of either the Set or the Reset inputs. By connecting a 2-input NAND gate in series with each input terminal of the SR Flip-flop a Gated SR Flip-flop can be created. This extra conditional input is called an "Enable" input and is given the prefix of "EN" as shown below.

When the Enable input "EN" is at logic level "0", the outputs of the two AND gates are also at logic level "0", (AND Gate principles) regardless of the condition of the two inputs S and R, latching the two outputs Q and Q into their last known state. When the enable input "EN" changes to logic level "1" the circuit responds as a normal SR bistable flip-flop with the two AND gates becoming transparent to the Set and Reset signals. This enable input can also be connected to a clock timing signal adding clock synchronisation to the flip-flop creating what is sometimes called a "Clocked SR Flip-flop".

So a Gated Bistable SR Flip-flop operates as a standard Bistable Latch but the outputs are only activated when a logic "1" is applied to its EN input and deactivated by a logic "0".

source : http://www.electronics-tutorials.ws/sequential/seq_1.html

SR Flip-Flop

2010-06-08T23:03:00.000-07:00

An SR Flip-Flop can be considered as a basic one-bit memory device that has two inputs, one which will "SET" the device and another which will "RESET" the device back to its original state and an output Q that will be either at a logic level "1" or logic "0" depending upon this Set/Reset condition. A basic NAND Gate SR flip flop circuit provides feedback from its outputs to its inputs and is commonly used in memory circuits to store data bits. The term "Flip-flop" relates to the actual operation of the device, as it can be "Flipped" into one logic state or "Flopped" back into another.

The simplest way to make any basic one-bit Set/Reset SR flip-flop is to connect together a pair of cross-coupled 2-input NAND Gates to form a Set-Reset Bistable or a SR NAND Gate Latch, so that there is feedback from each output to one of the other NAND Gate inputs. This device consists of two inputs, one called the Reset, R and the other called the Set, S with two corresponding outputs Q and its inverse or complement Q as shown below.

The SR NAND Gate Latch

The Set State

Consider the circuit shown above. If the input R is at logic level "0" (R = 0) and input S is at logic level "1" (S = 1), the NAND Gate Y has at least one of its inputs at logic "0" therefore, its output Q must be at a logic level "1" (NAND Gate principles). Output Q is also fed back to input A and so both inputs to the NAND Gate X are at logic level "1", and therefore its output Q must be at logic level "0". Again NAND gate principals. If the Reset input R changes state, and now becomes logic "1" with S remaining HIGH at logic level "1", NAND Gate Y inputs are now R = "1" and B = "0" and since one of its inputs is still at logic level "0" the output at Q remains at logic level "1" and the circuit is said to be "Latched" or "Set" with Q = "1" and Q = "0".

Reset State

In this second stable state, Q is at logic level "0", Q = "0" its inverse output Q is at logic level "1", not Q = "1", and is given by R = "1" and S = "0". As gate X has one of its inputs at logic "0" its output Q must equal logic level "1" (again NAND gate principles). Output Q is fed back to input B, so both inputs to NAND gate Y are at logic "1", therefore, Q = "0". If the set input, S now changes state to logic "1" with R remaining at logic "1", output Q still remains LOW at logic level "0" and the circuit's "Reset" state has been latched.

Truth Table for this Set-Reset Function

State	S	R	Q	Q
Set	1	0	1	0
Set	1	1	1	0
Reset	0	1	0	1
Reset	1	1	0	1
Invalid	0	0	1	1

It can be seen that when both inputs S = "1" and R = "1" the outputs Q and Q can be at either logic level "1" or "0", depending upon the state of inputs S or R BEFORE this input condition existed. However, input state R = "0" and S = "0" is an undesirable or invalid condition and must be avoided because this will give both outputs Q and Q to be at logic level "1" at the same time and we would normally want Q to be the inverse of Q. However, if the two inputs are now switched HIGH again after this condition to logic "1", both the outputs will go LOW resulting in the flip-flop becoming unstable and switch to an unknown data state based upon the unbalance. This unbalance can cause one of the outputs to switch faster than the other resulting in the flip-flop switching to one state or the other which may not be the required state and data corruption will exist. This unstable condition is known as its Meta-stable state.

Then, a bistable latch is activated or Set by a logic "1" applied to its S input and deactivated or Reset by a logic "1" applied to its R. The SR Latch is said to be in an "invalid" condition (Meta-stable) if both the Set and Reset inputs are activated simultaneously.

As well as using NAND Gates, it is also possible to construct simple 1-bit SR Flip-flops using two NOR Gates connected the same configuration. The circuit will work in a similar way to the NAND gate circuit above, except that the invalid condition exists when both its inputs are at logic level "1" and this is shown below.

The NOR Gate SR Flip-flop

source : http://www.electronics-tutorials.ws/sequential/seq_1.html

4000 series CMOS Logic ICs

2010-06-08T22:59:00.001-07:00

Quad 2-input gates

4001 quad 2-input NOR
4011 quad 2-input NAND
4030 quad 2-input EX-OR (now obsolete)
4070 quad 2-input EX-OR
4071 quad 2-input OR
4077 quad 2-input EX-NOR
4081 quad 2-input AND
4093 quad 2-input NAND with Schmitt trigger inputs

The 4093 has Schmitt trigger inputs to provide good noise immunity. They are ideal for slowly changing or noisy signals. The hysteresis is about 0.5V with a 4.5V supply and almost 2V with a 9V supply.

Triple 3-input gates

4023 triple 3-input NAND
4025 triple 3-input NOR
4073 triple 3-input AND
4075 triple 3-input OR

Notice how gate 1 is spread across the two ends of the package.

Dual 4-input gates

4002 dual 4-input NOR
4012 dual 4-input NAND
4072 dual 4-input OR
4082 dual 4-input AND

NC = No Connection (a pin that is not used).

4068 8-input NAND/AND* gate

This gate has a propagation time which is about 10 times longer than normal so it is not suitable for high speed circuits.

NC = No Connection (a pin that is not used).

* = The AND output (pin 1) is not available on some versions of the 4068.

4069 hex NOT (inverting buffer)

4049 hex NOT and 4050 hex buffer

4049 hex NOT (inverting buffer)
4050 hex non-inverting buffer

Inputs: These ICs are unusual because their gate inputs can withstand up to +15V even if the power supply is a lower voltage.

Outputs: These ICs are unusual because they are capable of driving 74LS gate inputs directly. To do this they must have a +5V supply (74LS supply voltage). The gate output is sufficient to drive four 74LS inputs.

NC = No Connection (a pin that is not used).

Note the unusual arrangement of the power supply pins for these ICs!

4000 dual 3-input NOR gate and NOT gate

Two 3-input NOR gates and a single NOT gate in one package.

NC = No Connection (a pin that is not used).

Decade and 4-bit Counters

4017 decade counter (1-of-10)

The count advances as the clock input becomes high (on the rising-edge). Each output Q0-Q9 goes high in turn as counting advances. For some functions (such as flash sequences) outputs may be combined using diodes.

The reset input should be low (0V) for normal operation (counting 0-9). When high it resets the count to zero (Q0 high). This can be done manually with a switch between reset and +Vs and a 10k resistor between reset and 0V. Counting to less than 9 is achieved by connecting the relevant output (Q0-Q9) to reset, for example to count 0,1,2,3 connect Q4 to reset.

The disable input should be low (0V) for normal operation. When high it disables counting so that clock pulses are ignored and the count is kept constant.

The ÷10 output is high for counts 0-4 and low for 5-9, so it provides an output at ¹/₁₀ of the clock frequency. It can be used to drive the clock input of another 4017 (to count the tens).

Example projects: Heart-shaped badge | Network Lead Tester | Traffic Light | Dice | Model Lighthouse

4026 decade counter and 7-segment display driver

The count advances as the clock input becomes high (on the rising-edge). The outputs a-g go high to light the appropriate segments of a common-cathode 7-segment display as the count advances. The maximum output current is about 1mA with a 4.5V supply and 4mA with a 9V supply. This is sufficient to directly drive many 7-segment LED displays. The table below shows the segment sequence in detail.

The reset input should be low (0V) for normal operation (counting 0-9). When high it resets the count to zero.

The disable clock input should be low (0V) for normal operation. When high it disables counting so that clock pulses are ignored and the count is kept constant.

The enable display input should be high (+Vs) for normal operation. When low it makes outputs a-g low, giving a blank display. The enable out follows this input but with a brief delay.

The ÷10 output (h in table) is high for counts 0-4 and low for 5-9, so it provides an output at ¹/₁₀ of the clock frequency. It can be used to drive the clock input of another 4026 to provide multi-digit counting.

The not 2 output is high unless the count is 2 when it goes low.

Example project: 'Random' flasher for 8 LEDs
This project uses the 4026 in an unconventional way, the outputs a-g and the ÷10 output (h) are used to flash individual LEDs in a complex pattern which appears random if not studied too closely!

4029 up/down synchronous counter with preset

The 4029 is a synchronous counter so its outputs change precisely together on each clock pulse. This is helpful if you need to connect the outputs to logic gates because it avoids the glitches which occur with ripple counters.

The count occurs as the clock input becomes high (on the rising-edge). The up/down input determines the direction of counting: high for up, low for down. The state of up/down should be changed when the clock is high.

For normal operation (counting) preset, and carry in should be low.

The binary/decade input selects the type of counter: 4-bit binary (0-15) when high; decade (0-9) when low.

The counter may be preset by placing the desired binary number on the inputs A-D and briefly making the preset input high. There is no reset input, but preset can be used to reset the count to zero if inputs A-D are all low.

Connecting synchronous counters in a chain: please see 4510/16 below.

4510 up/down decade (0-9) counter with preset
4516 up/down 4-bit (0-15) counter with preset

These are synchronous counters so their outputs change precisely together on each clock pulse. This is helpful if you need to connect their outputs to logic gates because it avoids the glitches which occur with ripple counters.

For normal operation (counting) preset, reset and carry in should be low. When reset is high it resets the count to zero (0000, QA-QD low). The clock input should be low when resetting.

The counter may be preset by placing the desired binary number on the inputs A-D and briefly making the preset input high, the clock input should be low when this happens.

Connecting synchronous counters in a chain
The diagram below shows how to link synchronous counters, notice how all the clock (CK) inputs are linked. Carry out (CO) feeds carry in (CI) of the next counter. Carry in (CI) of the first counter should be low for 4029, 4510 and 4516 counters.

4518 dual decade (0-9) counter
4520 dual 4-bit (0-15) counter

These contain two separate synchronous counters, one on each side of the IC.

Normally a clock signal is connected to the clock input, with the enable input held high. Counting advances as the clock signal becomes high (on the rising-edge). Special arrangements are used if the 4518/20 counters are linked in a chain, as explained below.

For normal operation the reset input should be low, making it high resets the counter to zero (0000, QA-QD low).

Counting to less than the maximum (9 or 15) can be achieved by connecting the appropriate output(s) to the reset input, using an AND gate if necessary. For example to count 0 to 8 connect QA (1) and QD (8) to reset using an AND gate.

Connecting 4518 and 4520 counters in a chain
The diagram below shows how to link 4518 and 4520 counters. Notice how the normal clock inputs are held low, with the enable inputs being used instead. With this arrangement counting advances as the enable input becomes low (on the falling-edge) allowing output QD to supply a clock signal to the next counter. The complete chain is a ripple counter, although the individual counters are synchronous! If it is essential to have truly synchronous counting a system of logic gates is required, please see a 4518/20 datasheet for further details.

7-bit, 12-bit and 14-bit counters

4020 14-bit (÷16,384) ripple counter

The 4020 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.

The count advances as the clock input becomes low (on the falling-edge), this is indicated by the bar over the clock label. This is the usual clock behaviour of ripple counters and it means a counter output can directly drive the clock input of the next counter in a chain.

Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q14 is 2¹⁴ = 16384 (¹/₁₆₃₈₄ of clock frequency). Note that Q2 and Q3 are not available.

The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low).

Also see: 4040 (12-bit) and 4060 (14-bit with internal oscillator).

4024 7-bit (÷128) ripple counter

The 4024 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.

Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q7 is 2⁷ = 128 (¹/₁₂₈ of clock frequency).

The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low).

4040 12-bit (÷4096) ripple counter

The 4040 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.

Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q12 is 2¹² = 4096 (¹/₄₀₉₆ of clock frequency).

The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low).

Also see these 14-bit counters: 4020 and 4060 (includes internal oscillator).

4060 14-bit (÷16,384) ripple counter with internal oscillator

The 4060 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.

Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q14 is 2¹⁴ = 16384 (¹/₁₆₃₈₄ of clock frequency). Note that Q1-3 and Q11 are not available.

The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low).

The 4060 includes an internal oscillator. The clock signal may be supplied in three ways:

From an external source to the clock input, as for a normal counter. In this case there should be no connections to external C and external R (pins 9 and 10).
RC oscillator as shown in the diagram. The oscillator drives the clock input with an approximate frequency f = ¹/_(2×R1×C) (it partly depends on the supply voltage). R1 should be at least 50k if the supply voltage is less than 7V. R2 should be between 2 and 10 times R1.
Crystal oscillator as shown in the diagram, note that there is no connection to pin 9. The 32768 Hz crystal will give a 2Hz signal at the last output, Q14.

Also see: 4020 (14-bit) and 4040 (12-bit), neither have internal oscillators.

Example projects: Christmas Decoration | Valentine Heart

Decoders

4028 BCD to decimal (1 of 10) decoder

The appropriate output Q0-9 becomes high in response to the BCD (binary coded decimal) input. For example an input of binary 0101 (=5) will make output Q5 high and all other outputs low.

The 4028 is a BCD (binary coded decimal) decoder intended for input values 0 to 9 (0000 to 1001 in binary). With inputs from 10 to 15 (1010 to 1111 in binary) all outputs are low.

Note that the 4028 can be used as a 1-of-8 decoder if input D is held low.

Also see: 4017 (a decade counter and 1-of-10 decoder in a single IC).

7-segment Display Drivers

4511 BCD to 7-segment display driver

The appropriate outputs a-g become high to display the BCD (binary coded decimal) number supplied on inputs A-D. The outputs a-g can source up to 25mA. The 7-segment display segments must be connected between the outputs and 0V with a resistor in series (330 with a 5V supply). A common cathode display is required.

Display test and blank input are active-low so they should be high for normal operation. When display test is low all the display segments should light (showing number 8). When blank input is low the display will be blank (all segments off).

The store input should be low for normal operation. When store is high the displayed number is stored internally to give a constant display regardless of any changes which may occur to the inputs A-D.

The 4511 is intended for BCD (binary coded decimal). Inputs values from 10 to 15 (1010 to 1111 in binary) will give a blank display (all segments off).

source : http://www.kpsec.freeuk.com/components/cmos.htm

Logic gate

2010-06-08T22:52:00.000-07:00

  
The 'Exclusive-NOR' gate circuit does the opposite to the EOR gate. It will give a low output if either, but not both, of its two inputs are high. The symbol is an EXOR gate with a small circle on the output. The small circle represents inversion.
The NAND and NOR gates are called universal functions since with either one the AND and OR functions and NOT can be generated.

Note:

A function in sum of products form can be implemented using NAND gates by replacing all AND and OR gates by NAND gates.

A function in product of sums form can be implemented using NOR gates by replacing all AND and OR gates by NOR gates.

Table 1: Logic gate symbols

Table 2 is a summary truth table of the input/output combinations for the NOT gate together with all possible input/output combinations for the other gate functions. Also note that a truth table with 'n' inputs has 2ⁿ rows. You can compare the outputs of different gates.

Table 2: Logic gates representation using the Truth table
 


source : http://www.ee.surrey.ac.uk/

AUDIO TRANSFORMERS

2009-02-13T01:04:00.000-08:00

What are audio transformers?

Audio transformers are "wide band" transformers. In essence a "transformer" is two or more windings coupled by a common magnetic field. It is this magnetic field which provides the means to pass voltages and currents from the primary winding to the secondary winding when alternating current flows.

Much which follows on the topic of audio transformers is of necessity somewhat over simplified to give a general overview. A transformer schematic is depicted in Figure 1 below.

Figure 1. - audio transformers schematic

Audio transformers were originally used in valve or tube amplifiers as interstage and output transformers. Early transistor amplifiers similarly used audio transformers for coupling and output stages.

There is nothing particularly mystical about audio transformers although their use is not particularly widespread today. I expect the greatest interest would come from people interested in restoring or building tube audio amplifiers. We will first consider the basic requirements.

We must assume fidelity is foremost in the minds of most restorers. Therefore the first requirement must be a relatively wide bandwidth, this is in the audio sense. My research into long forgotten and dusty, musty papers in my secret collection leads me to freshen my mind that audio transformer coupling is essentially applicable to power stages for impedance matching. Resistance-coupled amplifiers essentially produce undistorted output signal voltages regardless of plate-load-resistance value.

Maximum output power is produced when the impedance of the load matches the plate impedance of the tube. Using triodes, somewhat less output power but significantly less distortion results when the load impedance is between two to three times the plate impedance.

However tetrode or pentode tubes have very high plate impedances and the primary impedance of the coupling transformer is often between 1/10 to 1/5 of the tube plate impedance because it it not entirely feasible to produce audio transformers with primary impedances beyond 20K.

Primary impedance of audio transformers

Let us assume we are going to design a transformer of 20,000 ohms primary impedance. Now there is a direct mathematical relationship between the inductance of the primary, the design impedance and roll off frequencies. For very obvious reasons you would want steer somewhat clear of mains frequencies. One superior advantage of battery powered equipment is that "50 / 60 Hz mains hum" is not a problem. Of necessity because of the voltages involved all tube equipment derives its power from a "mains supply". Battling 50 / 60 Hz mains hum is an absolute pain so our theoretical transformer will begin "rolling off" at 100 Hz. Here is the formula.

Figure 2. - audio transformers formulas

In our fomula 4 * pi may be taken as 12.566, f is 100 Hz and of course R is 20,000 ohms. This formula is for a 3 dB roll off at 100 Hz. Substituting all those numbers into our formula and remembering all units are Henries, Ohms and Hertz we get a primary inductance of 15.92 Henries. That is a huge and possibly impossible value to obtain.

Looking through some data books...... if there is sufficient interest.

Got a question on this topic?

If you are involved in electronics then consider joining our "electronics Questions and Answers" news group to ask your question there as well as sharing your thorny questions and answers. Help out your colleagues!.

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SOURCE: http://www.electronics-tutorials.com/basics/audio-transformers.htm

TRANSFORMERS

2009-02-13T01:02:00.000-08:00

What are transformers?

The name transformers is derived from the fact that when two coils are placed in close inductive proximity to one another the lines of force from one cut across the the turns of the other inducing an ac current, energy is transformed from one winding to another and this is called transformer action.

There are a great variety of transformers for a variety of applications including power transformers, audio transformers and rf transformers among others. All work on the above principle.

Power transformers

As the name implies a power transformer is designed to usually translate voltage from one level to another. Another type called a current transformer will not be discussed here. The schematic of a transformer is depected in figure 1 below. Consider also the topics covered under power supplies where power transformers are used.

Figure 1. - general transformer schematic

Some power transformers have a centre tap on the secondary side. Note in figure 1 above the left hand side is usually denoted the "primary" whilst the right hand side is denoted the power transformers "secondary" side. Most power transformers are designed for frequencies in the region of 50 / 60 Hz which are the principle mains frquencies around the world.

Some examples of power transformers are shown in figure 2 below.

Figure 1. - photograph of different types of power transformers

The transformer on the upper left has "flying leads" for, in the case of all these transformers, the incoming voltage is the Australian standard 240V AC. The secondary side has three "lugs" to connect to and this is a 240V - 6.3V CT transformer.

The transformer on the upper right hand side is a multi-tap type with "flying leads" on both sides. The output allows you to select 6.3V, 9V, 12V and 15V depending upon your requirements, maximum current is 1A.

The transformer on the bottom left is called a "plug pack" in Australia. This one plugs directly into a power point and because a rectifier is included within the plug pack it produces 12DC @ 1A on its output. Note the four way connector

shown at the centre, very bottom of the picture. This connector is designed to connect to the four sockets the manufacturer considers most popular.

The power transformer on the bottom right has a bit more "grunt" but only providing "lugs" for connecting leads. It is also a "multi-tap" type but designed to provide 2 amps.

Modern power transformers are wound on a "bobbin" which fits a core manufactured of materials to suit mains frequencies. The power handling capacity of a power transformer is determined by the physical size of the core and its properties. Design information is available from manufacturers. Ultimately the design information will provide the number of turns per volt. It is important to note that "toroid" power transformers are becoming increasingly popular and can handle larger amounts of power for the same physical dimensions and are thought by many "experts" to offer superior performance, particularly in higher power audio amplifiers.

The relationship of turns per volt holds good for both primary and secondary. A transformer designed for a nominal 250V AC input and a nominal 6.3V secondary output has a turns ratio of 250 / 6.3 or about 40:1

"Good design" usually leads to the cross-sectional "copper" areas of both the primary and the secondary being equal. Purely by way of illustration and not necessarily related to the real world, if the primary consisted of 2,400 turns of #34 gauge wire which is 0.16mm dia we would have a total cross sectional area of:

2,400 * [(0.16 ² * pi) / 4]. Where [(pi X D ²) / 4] is the customary formula to determine the area of a circular object.

Here you should get 2400 X 0.0201 = 48.24 mm ²

Therefore if our turns ratio was 20:1 for a 12V secondary, we would get 200 turns secondary still occupying approximately 48.24 mm ². With a little high school algebra we determine this gives us a secondary diameter of 0.55 mm diameter which is around about #24 gauge wire.

CAUTION: Of necessity I have greatly simplified the above to give a broad overview of how power transformers are designed. Always consult manufacturers such as Magnetics for tables and correct design information.

Remember "electricity KILLS!". Home construction of power transformers is a lost cause because the cost of component parts will always greatly exceed the cost of an off-the-shelf transformer.

Audio transformers

Essentially the main purpose of an interstage audio transformer is to isolate the DC and couple the signal, with minimal loss. The transformer windings look like short circuits to DC, yet are seen as complex impedances to the AC signal. Much which is contained on the topic of audio transformers is of necessity somewhat over simplified to give a general overview.

Go to: Audio Transformers

RF transformers

RF transformers generally fall into two categories, band pass filters and broad band transformers. Bandpass filters might well fall into the category of those used in IF amplifier filters while broad band transformers are generally used for impedance matching.

Figure 3. - schematic of an rf transformer

The type of broad band transformer depicted in figure 3 is often wound on a ferrite toroid of sufficient permeability to give a reactance of about 5 tomes the highest impedance at the lowest frequency of interest.

SOURCE: http://www.electronics-tutorials.com/basics/transformers.htm

TRANSISTORS

2009-02-13T00:55:00.000-08:00

Introduction to transistors?

Transistors, I was once told, "were the fastest acting fuse known to mankind". This of course was a reference to the fact an early transistor was intolerant of fault conditions whereas in years gone by, vacuum tubes (valves) would cop a lot of abuse. Just remember that fact. [one of "murphy's laws" - The component exists to protect the fuse]

Generally transistors fall into the category of bipolar transistor, either the more common NPN bipolar transistors or the less common PNP transistor types. There is a further type known as a FET transistor which is an inherently high input impedance transistor with behaviour somewhat comparable to valves. Modern field effect transistors or FET's including JFETS and MOSFETS now have some very rugged transistor devices. I am often asked about the term "bipolar" - see later.

History of Transistors

The transistor was developed at Bell Laboratories in 1948. Large scale commercial use didn't come until much later owing to slow development. Transistors used in most early entertainment equipment were the germanium types. When the silicon transistor was developed it took off dramatically. The first advantages of the transistor were relatively low power consumption at low voltage levels which made large scale production of portable entertainment devices feasible. Interestingly the growth of the battery industry has paralleled the growth of the transistor industry. In this context I include integrated circuits which of course are simply a collection of transistors grown on the one silicon substrate.

How do transistors work?

Transistors work on the principle that certain materials e.g. silicon, can after processing be made to perform as "solid state" devices. Any material is only conductive in proportion to the number of "free" electrons that are available. Silicon crystals for example have very few free electrons. However if "impurities" (different atomic structure - e.g. arsenic) are introduced in a controlled manner then the free electrons or conductivity is increased. By adding other impurities such as gallium, an electron deficiency or hole is created. As with free electrons, the holes also encourage conductivity and the material is called a semi-conductor. Semiconductor material which conducts by free electrons is called n-type material while material which conducts by virtue of electron deficiency is called p-type material.

How do holes and electrons conduct in transistors?

If we take a piece of the p-type material and connect it to a piece of n-type material and apply voltage as in figure 1 then current will flow. Electrons will be attracted across the junction of the p and n materials. Current flows by means of electrons going one way and holes going in the other direction. If the battery polarity were reversed then current flow would cease.

Figure 1. - electron flow in a p-n juction of a diode

Some very interesting points emerge here. As depicted in figure 1 above a junction of p and n types constitutes a rectifier diode. Indeed a transistor can be configured as a diode and often are in certain projects, especially to adjust for thermal variations. Another behaviour which is often a limitation and at other times an asset is the fact that with zero spacing between the p and n junctions we have a relatively high value capacitor.

This type of construction places an upper frequency limit at which the device will operate. This was a severe early limitation on transistors at radio frequencies. Modern techniques have of course overcome these limitations with some bipolar transistors having Ft's beyond 1 Ghz. The capacitance at the junction of a diode is often taken advantage of in the form of varactor diodes. See the tutorial on diodes for further details. The capacitance may be reduced by making the junction area of connection as small as possible. This is called a "point contact".

Now a transistor is merely a "sandwich" of these devices. A PNP transistor is depicted in figure 2 below.

Figure 2. - sandwich construction of a PNP transistor

Actually it would be two p-layers with a "thin" n-layer in between. What we have here are two p-n diodes back to back. If a positive voltage (as depicted) is applied to the emitter, current will flow through the p-n junction with "holes" moving to the right and "electrons moving to the left. Some "holes" moving into the n-layer will be neutralised by combining with the electrons. See electron theory and atoms. Some "holes" will also travel toward the right hand region.

The fact that there are two junctions leads to the term "bipolar transistor".

If a negative voltage (as depicted) is applied to the collector of the transistor, then ordinarily no current flows BUT there are now additional holes at the junction to travel toward point 2 and elctrons can travel to point 1, so that a current can flow, even though this section is biased to prevent conduction.

It can be shown that most of the current flows between points 1 and 2. In fact the amplitude (magnitude) of the collector current in a transistor is determined mainly by the emitter current which in turn is determined by current flowing into the base of the transistor. Consider the base to be a bit like a tap or faucet handle.

Transistor amplification

Because the collector current (where the voltage is relatively high) is pretty much the same as the emitter current and also controlled by the emitter current (where the voltage is usually much lower) it can be shown by ohms law

P = I ² X R

that amplification occurs. See small signal amplifiers.

The NPN transistor

We discussed a PNP transistor above. The only differences between PNP and NPN transistors are in manufacturing (i.e. location of the p-layers and n-layers) and of much importance in the biasing. The schematic symbols for PNP and NPN transistors, (the work horse is the NPN) are shown in figure 3 below. A silicon NPN transistor needs to be forward biased by about 0.65V for it to turn on.

Historical Footnote on Transistors - [added 1st May, 2000]

This is an interesting excerpt from a post by a friend to a list I subscribe to:

"The more I think about Tesla the more it brings to mind another bright guy that got off track and missed out. His name was Shockley. I worked for him in the early days of Silicon Valley".

"He had the technology and the people to put the 'silicon transistor' on the market, BUT he was obsessed with a thing he called the "four layer diode" to be used for telephone switching. That product finally went nowhere and the guys that left Shockley and started Fairchild Semiconductor were the guys that marketed the transistor in it's first commercial silicon form".

"And the four layer diode?, finally turned out to be the SCR, a good product but not the world beater that the silicon transistor was".

[end historical footnote]

Meanwhile back to our transistor tutorial and figure 3 depicting a schematic of a PNP transistor and an NPN transistor.

Figure 3. - schematic of PNP transistor and NPN transistor

Notice the only difference is the location and direction of the arrows in the emitter. This denotes direction of current flow in the emitter. Note: that is not a topic I will enter into discussion as I've seen too many discussions already - I have no opinion .

Also see small signal amplifiers.

Download PDF data sheet P2N2222A - plastic bipolar transistor 238K

FET's as transistors

In figure 4 below I have depicted the schematics of the two most popular types. A J-FET and a dual gate mosfet. Typical types might be MPF-102 for a J-FET and the old RCA 40673 for the dual gate.

Figure 4. - schematic of J-FET transistor and dual gate mosfet transistor

The FET of course is characterised by its extremely high input impedance. Some people claim the FET is a superior device to a bipolar transistor. I consider that to be a subjective opinion with the proviso that FET development has led to some amazing developments, particularly with power-fets.

I won't go into any length about how FETS operate except to point out the principal differences to NPN and PNP transistors. A bipolar transistor has moderate input impedance (depending on configuration) while some FETs can and do have input impedances measured in megohms. Bipolar transistors are essentially "current" amplifiers while FETS could be considered voltage amplifiers.

Download PDF data sheet MPF-102 J-FET 270K

How are semiconductors made?

Strictly speaking this tutorial presented by Harris Semiconductor applies more to integrated circuits but the principle remains much the same.

The process of manufacturing semiconductors, or integrated circuits (commonly called ICs, or chips) typically consists of more than a hundred steps, during which hundreds of copies of an integrated circuit are formed on a single wafer.

Generally, the process involves the creation of eight to 20 patterned layers on and into the substrate, ultimately forming the complete integrated circuit. This layering process creates electrically active regions in and on the semiconductor wafer surface.
See - http://rel.intersil.com/docs/lexicon/manufacture.html

BOOK - The Transistor Handbook by Cletus J. Kaiser

SOURCE: http://www.electronics-tutorials.com/basics/transistors.htm

DIODES

2009-02-13T00:54:00.000-08:00

What are Diodes?

Diodes are semiconductor devices which might be described as passing current in one direction only. The latter part of that statement applies equally to vacuum tube diodes. Diodes however are far more versatile devices than that. They are extremely versatile in fact. It might pay you to review the topic of Electron theory and atoms

Diodes can be used as voltage regulators, tuning devices in rf tuned circuits, frequency multiplying devices in rf circuits, mixing devices in rf circuits, switching applications or can be used to make logic decisions in digital circuits. There are also diodes which emit "light", of course these are known as light-emitting-diodes or LED's. As we say diodes are extremely versatile.

Schematic symbols for Diodes

A few schematic symbols for diodes are:

Figure 1 - schematic symbols for diodes

Types of Diodes

The first diode in figure 1 is a semiconductor diode which could be a small signal diode of the 1N914 type commonly used in switching applications, a rectifying diode of the 1N4004 (400V 1A) type or even one of the high power, high current stud mounting types. You will notice the straight bar end has the letter "k", this denotes the "cathode" while the "a" denotes anode. Current can only flow from anode to cathode and not in the reverse direction, hence the "arrow" appearance. This is one very important property of diodes.

The second of the diodes is a zener diode which are fairly popular for the voltage regulation of low current power supplies. Whilst it is possible to obtain high current zener diodes, most regulation today is done electronically with the use of dedicated integrated circuits and pass transistors.

The next of the diodes in the schematic is a varactor or tuning diode. Depicted here is actually two varactor diodes mounted back to back with the DC control voltage applied at the common junction of the cathodes. These cathodes have the double bar appearance of capacitors to indicate a varactor diode. When a DC control voltage is applied to the common junction of the cathodes, the capacitance exhibited by the diodes (all diodes and transistors exhibit some degree of capacitance) will vary in accordance with the applied voltage. A typical example of a varactor diode would be the Philips BB204G tuning diodes of which there are two enscapsulated in a TO-92 transistor package. At a reverse voltage Vr (cathode to anode) of 20V each diode has a capacitance of about 16 pF and at Vr of 3V this capacitance has altered to about 36 pF. Being low cost diodes, tuning diodes have virtually replaced air variable capacitors in radio applications today.

The next diode is the simplest form of vacuum tube or valve. It simply has the old cathode and anode. These terms were passed on to modern solid state devices. Vacuum tube diodes are mainly only of interest to restorers and tube enthusiasts.

The last diode depicted is of course a light emitting diode or LED. A led actually doesn't emit as much light as it first appears, a single LED has a plastic lens installed over it and this concentrates the amount of light. Seven LED's can be arranged in a bar fashion called a seven segment LED display and when decoded properly can display the numbers 0 - 9 as well as the letters A to F.

Rectifying Diodes

The principal early application of diodes was in rectifying 50 / 60 Hz AC mains to raw DC which was later smoothed by choke transformers and / or capacitors. This procedure is still carried out today and a number of rectifying schemes for diodes have evolved, half wave, full wave and bridge rectifiers.

Figure 2 - rectifying diodes

As examples in these applications the half wave rectifier passes only the positive half of successive cycles to the output filter through D1. During the negative part of the cycle D1 does not conduct and no current flows to the load. In the full wave application it essentially is two half wave rectifiers combined and because the transformer secondary is centre tapped, D1 conducts on the positive half of the cycle while D2 conducts on the negative part of the cycle. Both add together. This is more efficient. The full wave bridge rectifier operates essentially the same as the full wave rectifier but does not require a cetre tapped transformer. Further discussion may be seen on the topic power supplies.

A further application of rectifying diodes is in the conversion or detection of rf modulated signals to audio frequencies. Typical examples are am modulated signals being detected and early detection schemes for fm also used diodes for detecting modulation.

Voltage Regulating Diodes

For relatively light current loads zener diodes are a cheap solution to voltage regulation. Zener diodes work on the principle of essentially a constant voltage drop at a predetermined voltage (determined during manufacture). An example is a Philips BZX79C12 type with a regulation range between 11.4V and 12.7V but typically 12V and a total power dissipation of 500 mW in a DO-35 package. The dissipation can be extended by using a series pass transistor, see power supplies. Notice in figure 3 there is a resistor to miminmise current drawn but mainly as an aid to dropping the supply voltage and reducing the burden on the zener diodes.

Figure 3 - zener voltage regulation diodes

In the second schematic of figure 3 we have three zener diodes in series providing voltages of 5V, 10V, 12V, 22V and 27V all from a 36V supply. This configuration is not necessarily recommended especially when the current being drawn is seriously mismatched between voltages. It is presented purely out of interest.

Varactor or Tuning Diodes

These types of diodes work on the principle that all diodes exhibit some capacitance. Indeed the zener diode BZX79C12 quoted above has, according to the data book, a capacitance of 65-85 pF at 0V and measured at 1 Mhz.

For AM Radio band applications a specific diode has been devised. The Philips BB212 in a TO-92 case is one such type. Each of the diodes has a capacitance of 500 - 620 pF at a reverse bias of 0.5V and <22>

Several obvious advantages come immediately to mind, a small transistor type package, very low cost, ease of construction on a circuit board, can be mounted away from heat generating devices, frequency determining circuitry entirely dependent upon resistor values and ratios, DC voltage control can be either from frequency synthesiser circuits or perhaps a multi-turn potentiometer. Such a potentiometer aids band spreading and fine tuning if two potentiometers are used. The only real limitation is your imagination and the calculations involved.

Diodes as frequency multipliers

Just one more example of the versatility of diodes is the frquency doubling circuit depicted in Figure 4. Now if that looks a lot like the full wave rectifier from figure 2 above you would be correct. That is why the ripple frequency for 50 / 60 Hz always comes out at 100 / 120 Hz.

Figure 4 - diodes as frequency multipliers

Here the input is a wide band transformer and the signal passes to a full wave rectifier comprising two 1N914 diodes. The DC component caused by the rectification passes to ground through RFC which of course presents a high impedance to the rf porion of the signal but essentially a short circuit for DC. The original signal should be down about 40 dB and with this type of circuit there would be a loss of somewhere around 7.5 dB so the 2 X signal would require further amplification to restore that loss.

Diodes as mixers

With some subtle re-arrangement to figure 4 we can get the circuit to function as a two diode frequency mixer. Note that there are other diode arrangements as well in this application. See mixers.

Figure 5 - diodes as frequency mixers

The diodes here act as switches and it can be mathematically shown that only the sum and difference signals will result. For example, if F1 was 5 Mhz and F2 was 3 Mhz then the sum and difference signals from the diodes would be 8 Mhz and 2 Mhz. None of the original signals appear at the output and this is a most important property of using diodes as mixers.

It should be noted that although 1N914 diodes are depicted you would normally use hot carrier diodes in any serious application and the diodes need to be well matched.

Applications of switching Diodes

Similar types of diodes have been developed specifically for band switching purposes. Although a typical 1N914 type switching diode can be used for such purposes it is preferable to use diodes which have been optimised for such purposes because the Rd on is much lower. This means the diode resistance Rd can have a serious affect on rf circuits in particular the "Q" of a tuned circuit. One example of a low Rd device is the Philips BA482 diode used for band switching in television tuners. It has a typical Rd of 0.4 ohms at a forward current of 10 mA.

In figure 5 we have one application where switching diodes operate. All diodes serve to switch in or out capacitors in the diagram which is presented here just to illustrate one single application of switching diodes, many, many more applications exist. Again the limit is your imagination.

Figure 6 - applications of switching diodes

The switching diodes in figure 4 switch in or out successively higher values of capacitors as each control select line is "grounded". The voltage from the +5V feed line proceeds through the diode at DC thus opening the diode and making it appear "transparent" for rf purposes. The capacitor with the value attached is then "switched" into circuit. Other components marked RFC and Cbp are chokes and bypass capacitors for "clean" switching. The bypass capacitors and choke values would be determined by the frequency of operation.

We could just have easily have switched inductors instead of capacitors. Note why Rd is quite important on overall circuit performance. If we were using inductors the diode resistance Rd would have a significant affect on inductor "Q" which in turn would affect filter performance, if it was in fact an LC filter application.

Switching Diodes in Logic Circuits

If you you completed the tutorial on digital basics you should be aware of binary numbers. There are a whole range of digital building blocks available and just by way of one illustration of using diodes we have presented the 74HC4040 twelve stage binary ripple counter (there are others with varying number of stages).

In the schematic of figure 7 we have this counter which divides by successive division of two for twelve stages. Initially because there is no voltage drop across the resistor a high appears on all anodes as well as on pin 4 the master reset causing the counter to reset forcing all outputs low and in turn a voltage drop across each diode and across the resistor and a low on reset.

Progressively each of the outputs change from low to high for a certain period of time and without unduly complicating matters when all outputs as selected by our diode combination (in this particular case 1 + 2 + 32 + 64 = 99) are simultaneously high the voltage drop across the resistor will cease and cause pin 11 (reset which was formerly low) to go high and reset all the internal ripple counters.

Figure 7 - applications of switching diodes in digital logic circuits

At the same time pin 4 changes state also with reset. It can been shown this happens once every 99 periods. Simply by placing diodes on the right outputs we can select to divide by any number up to 4095 using this particular counter.

Light-Emitting-Diodes or LED's

Many circuits use a led as a visual indicator of some sort even if only as an indicator of power supply being turned on. A sample calculation of the dropping resistor is included in figure 8.

Figure 8 - connecting light emitting diodes (LED's) to supply

Most leds operate at 1.7V although this is not always the case and it is wise to check. The dropping resistor is simply the net of supply voltage minus the 1.7V led voltage then divided by the led brightness current expressed as "amps" (ohms law). Note the orientation of both cathode and anode with respect to the ground end and the supply end. Usually with a led the longer lead is the anode.

If you would like to see some "REAL BIG" diodes then this is the site to go to:
Power Silicon Rectifier Diodes.

BOOK - The Diode Handbook by Cletus J. Kaiser

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IMPEDANCE

2009-02-13T00:52:00.000-08:00

What is impedance?

First comes the simple answer. If the demand exists we will provide a complex answer to impedance later.

Now here comes one of the most confusing aspects of electronics - which I will de-mystify by taking an extremely casual approach, so what's new!. I have known electronic enthusiasts who still couldn't even mentally visualise the concept even after 25 years.

I'll keep it dead simple, very inelegant but dead simple and give all the purists heart palpitations. I bet you walk away with a better understanding though.

If you need to know the technical answer for impedance and you should, then consult one of the must read texts I will have suggested elsewhere.

A simple example of impedance

Assume you have available these 4 items on your bench:

(a) A series of eight fresh AA type 1.5 volt cells to create a total of 12 volts supply.
(b) A 12 volt heavy duty automotive battery - fully charged.
(c) a small 12v bulb (globe) of very, very low wattage. and;
(d) a very high wattage automotive high-beam headlight.

Now if we connect the extremely low wattage bulb to the series string of AA cells we would expect all to work well. Similarly if we connect the high wattage, high-beam headlight to the heavy duty automotive battery all will be well. Well for a time anyway. Both of these sets are "sort"of matched together. Light duty to light duty and heavy duty to heavy duty.

Now what do you think would happen if we connect the high beam headlightto the series AA cells and conversely the low wattage bulb to the automotive battery?.

In the first case we could imagine the high beam headlight would quickly trash our little tiny AA cells. In the second case our min-wattage bulb would glow quite happily at its rated wattage for quite a long time. Why?, therein lies my expanation of impedance. Consider it!

The heavy duty battery is capable of delivering relatively large amounts of power but the series string is capable of delivering only relatively minimal power. The first is a low impedance sourceand the other, in comparison is a relatively high impedance source.

On the other hand the high beam headlight is capable of consuming relatively large amounts of power but the minature bulb is capable of consuming only minimal amounts of power.

High Impedance loads and Low Impedance loads

Again the first is a low impedance load and the other is high impedance load. If you're keen to apply ohms law you will discover why, research it through the text books.

Meanwhile take a well deserved coffee or tea break now and think it over. Me?, I'll just have another beer while I'm waiting for you.

Good break?. If you were paying attention you would now be able to understand an analogy - a particularly rough but effective one;

Imagine a tiny caterpiller chewing on a large blade of grass - no problem plenty to eat there. Now on the other hand imagine a poor cow stuck in a desert with only one similar blade of grass available to eat. I hope you have some better understanding now.

General expression of Impedance

The term impedance is a general expression which can be applied to any electrical entity which impedes the flow of current. Thus this expression could be used to denote a resistance, a pure reactance, or as is most likely in the real world, a complex combination of both reactance and resistance.

Don't get overly concerned if you're a bit confused by that statement at the moment. However this does then lead us on to "Q".

Footnote on Impedance - 10th April, 2002

A reader wrote to me and suggested:

Hi Ian,

Thanks for the great site. I find it absolutely invaluable. It's rare to find find such high quality, free information.

I finally got the concept of impedance matching through my head. Here is a point that you might add to you discussion on impedance and the lightbulb/battery analogy:

When mismatched, neither system will deliver its designed light output. The high current bulb will deliver very little light energy when powered by the low current batteries. The low current bulb will only deliver a fraction of the light energy that the high current battery is capable of deliving. But, match the sources to the loads, and both systems run at 100% efficiency!

BOOK - A Practical Introduction to Impedance Matching by Robert L. Thomas

SOURCE: http://www.electronics-tutorials.com/basics/impedance.htm

RESONANCE

2009-02-13T00:38:00.000-08:00

What is resonance?

Resonance occurs when the reactance of an inductor balances the reactance of a capacitor at some given frequency. In such a resonant circuit where it is in series resonance, the current will be maximum and offering minimum impedance. In parallel resonant circuits the opposite is true.

Resonance formula

The formula for resonance is:

2 * pi * f * L = 1 / (2 * pi * f * C)

where: 2 * pi = 6.2832; f = frequency in hertz L = inductance in Henries and C = capacitance in Farads

Which leads us on to:

f = 1 / [2 * pi (sqrt LC)]

where: 2 * pi = 6.2832; f = frequency in hertz L = inductance in Henries and C = capacitance in Farads

A particularly simpler formula for radio frequencies (make sure you learn it) is:

LC = 25330.3 / f ²

where: f = frequency in Megahertz (Mhz) L = inductance in microhenries (uH) and C = capacitance in picofarads (pF)

Following on from that by using simple algebra we can determine:

LC = 25330.3 / f ² and L = 25330.3 / f ² C and C = 25330.3 / f ² L

Impedance at Resonance

In a series resonant circuit the impedance is at its lowest for the resonant frequency whereas in a parallel resonant circuit the impedance is at its greatest for the resonant frequency. See figure 1.

Figure 1 - resonance in series and parallel circuits

"For a series circuit at resonance, frequencies becoming far removed from resonance see an ever increasing impedance. For a parallel circuit at resonance, frequencies becoming far removed from resonance see an ever decreasing impedance".

That was a profoundly important statement. Please read it several times to fully understand it.

A typical example to illustrate that statement are the numerous parallel circuits used in radio. Look at the parallel resonant circuit above. At resonance that circuit presents such a high impedance to the resonant circuit to the extent it is almost invisible and the signal passes by. As the circuit departs from its resonant frequency, up or down, it presents a lessening impedance and progressively allows other signals to leak to ground. At frequencies far removed from resonance, the parallel resonant circuit looks like a short path to ground. For series resonance the opposite is true.

source: http://www.electronics-tutorials.com/basics/resonance.htm

REACTANCE

2009-02-13T00:34:00.000-08:00

What is reactance?

Reactance is the property of resisting or impeding the flow of ac current or ac voltage in inductors and capacitors. Note particularly we speak of alternating current only ac, which expression includes audio af and radio frequencies rf. NOT direct current dc.

Inductive Reactance

When ac current flows through an inductance a back emf or voltage develops opposing any change in the initial current. This opposition or impedance to a change in current flow is measured in terms of inductive reactance.

Inductive reactance is determined by the formula:

2 * pi * f * L

where: 2 * pi = 6.2832; f = frequency in hertz and L = inductance in Henries

Capacitive Reactance

When ac voltage flows through a capacitance an opposing change in the initial voltage occurs, this opposition or impedance to a change in voltage is measured in terms of capacitive reactance.

Capacitive reactance is determined by the formula:

1 / (2 * pi * f * C)

where: 2 * pi = 6.2832; f = frequency in hertz and C = capacitance in Farads

Some examples of Reactance

What reactance does a 6.8 uH inductor present at 7 Mhz? Using the formula above we get:

2 * pi * f * L

where: 2 * pi = 6.2832; f = 7,000,000 Hz and L = .0000068 Henries

Answer: = 299 ohms

What reactance does a 33 pF capacitor present at 7 Mhz? Using the formula above we get:

1 / (2 * pi * f * C)

where: 2 * pi = 6.2832; f = 7,000,000 Hz and C = .0000000000033 Farads

Answer: = 689 ohms

Now in the real world we don't use big numbers like that, we use exponentials on our pocket calculator to get numbers like this:

For inductive reactance

where: 2 * pi = 6.2832; f = 7 X 10⁺⁶ Hz and L = 6.8 X ^-6 Henries

Answer: = 299 ohms

For capacitive reactance

1 / (2 * pi * f * C)

where: 2 * pi = 6.2832; f = 7 X 10⁺⁶ Hz and C = 33 X ^-12 Farads

Answer: = 689 ohms

Got a question on this topic?

The absolute fastest way to get your question answered and yes, I DO read most posts.

This is a mutual help group with a very professional air about it. I've learn't things. It is an excellent learning resource for lurkers as well as active contributors.

2009-01-19T03:00:00.001-08:00

INDUCTANCE

What is inductance?

The property of inductance might be described as "when any piece of wire is wound into a coil form it forms an inductance which is the property of opposing any change in current". Alternatively it could be said "inductance is the property of a circuit by which energy is stored in the form of an electromagnetic field".

We said a piece of wire wound into a coil form has the ability to produce a counter emf (opposing current flow) and therefore has a value of inductance. The standard value of inductance is the Henry, a large value which like the Farad for capacitance is rarely encountered in electronics today. Typical values of units encountered are milli-henries mH, one thousandth of a henry or the micro-henry uH, one millionth of a henry.

A small straight piece of wire exhibits inductance (probably a fraction of a uH) although not of any major significance until we reach UHF frequencies.

The value of an inductance varies in proportion to the number of turns squared. If a coil was of one turn its value might be one unit. Having two turns the value would be four units while three turns would produce nine units although the length of the coil also enters into the equation.

Inductance formula

The standard inductance formula for close approximation - imperial and metric is:

imperial measurements

L = r² X N² / ( 9r + 10len )

where:
L = inductance in uH
r = coil radius in inches
N = number of turns
len = length of the coil in inches

metric measurements

L = 0.394r² X N² / ( 9r + 10len )

where:
L = inductance in uH
r = coil radius in centimetres
N = number of turns
len = length of the coil in centimetres

[ADDED 22nd May, 2002] Someone asked about a formula which takes into account the spacing bewtween windings, the 10len above automatically takes that into account, if you're confused think about it!.

High "Q" Inductance formula

It has been found that the optimum dimensions for a high "Q" air core inductor is where the length of the coil is the same as the diameter of the coil. A simplified formula for inductance has been derived to establish the required number of turns for a given inductance value.

metric measurements

N = SQRT [( 29 * L ) / (0.394r)]

where:
L = inductance in uH
r = coil radius in centimetres
N = number of turns

Solenoid Inductors

Coils wound on a former (with or without a core) may have multilayers of windings which are called solenoid windings.

Self Resonant Frequency of an Inductance

All coils also exhibit a degree of self-capacitance caused by minute capacitances building up around and between adjacent windings.

Depending upon the application this may be of considerable concern. This self-capacitance combined with the natural inductance will form a resonant circuit (self-resonant frequency) limiting the useful upper frequency of the coil. There are special winding techniques to to use on occassion to minimise this self capacitance.

Iron Cores

If the coil is wound on an iron core the inductance is greatly increased and the magnetic lines of force increase proportionally. This is the basis of electro-magnets used in solenoid valves and relays.

Power Transformers

When the coil is wound on special iron laminations or cores and a second winding is placed on the core a "transformer" results. This is the basis of all power transformers although only alternating current (a.c.) can be transformed. The voltage relationship in transformers is proportional to the turns. For example a power transformer might have 2,500 turns on the primary side and the secondary side might have 126 turns. Such a relationship is 250 : 12.6 and if the primary were connected to 250V a.c. the secondary would produce a voltage of 12.6V a.c.

Interesting, if the core size and the wire diameter on the primary supported a primary current of 100 mA, the the primary power available would be 250V X 100 mA or 250 X 0.1 = 25 watts. Ignoring core and copper losses we could say that 25 watts is now available on the secondary side at 12.6V which is 25W / 12.6V = 1.98 amps. In practice we don't get that kind of efficiency however it would pay to remember that most power transformers are designed to function most efficient at or near full design load.

R.F. Transformers

In many radio applications the coil is wound on a ferrite or powdered iron core. Typical examples are the ferrite rod receiving antenna used in cheap transistor radios or the i.f. transformers enclosed in metal cans in those radios - red, yellow, black, green cores. The core is manufactured to be optimum for the frequency range of interest and greatly enhances the inductance for a specific number of turns. If we wound a coil on a blank former we might get an inductance of say 10 uH, adding a specific core might increase the inductance to 47 uH. By using screw in / screw out cores (as in the metal cans) we can vary the inductance over a fair range of interest.

A home made Coil Winder by Lloyd Godsey KK7IZ - PDF File 473kB

BOOK - Inductor Handbook by Cletus J. Kaiser

SOURCE: http://www.electronics-tutorials.com/basics/inductance.htm

2009-01-19T02:58:00.000-08:00

CAPACITANCE

What is capacitance?

In the topic current we learnt of the unit of measuring electrical quantity or charge was a coulomb. Now a capacitor (formerly condenser) has the ability to hold a charge of electrons.

The number of electrons it can hold under a given electrical pressure (voltage) is called its capacitance or capacity. Two metallic plates separated by a non-conducting sunstance between them make a simple capacitor. Here is the symbol of a capacitor in a pretty basic circuit charged by a battery.

Figure 1. - capacitor schematic in a circuit

In this circuit when the switch is open the capacitor has no charge upon it, when the switch is closed current flows because of the voltage pressure, this current is determined by the amount of resistance in the circuit. At the instance the switch closes the emf forces electrons into the top plate of the capacitor from the negative end of the battery and pulls others out of the bottom plate toward the positive end of the battery.

Two points need to be considered here. Firstly as the current flow progresses more electrons flow into the capacitor and a greater opposing emf is developed there to oppose further current flow, the difference between battery voltage and the voltage on the capacitor becomes less and less and current continues to decrease. When the capacitor voltage equals the the battery voltage no further current will flow.

The second point is if the capacitor is able to store one coulomb of charge at one volt it is said to have a capacitance of one Farad. This is a very large unit of measure. Power supply capacitors are often in the region of 4,700 uF or 4,700 / millionths of a Farad. Radio circuits often have capacitances down to 10 pF which is 10 / million, millionths of a Farad.

The unit uF stands for micro-farad (one millionth) and pF stands for pico-farad (one million, millionths). These are the two common values of capacitance you will encounter in electronics.

Time constant of capacitance

The time required for a capacitor to reach its charge is proportional to the capacitance value and the resistance value.

The time constant of a resistance - capacitance circuit is:

T = R X C

where T = time in seconds
where R = resistance in ohms
where C = capacitance in farads

The time in this formula is the time to acquire 63% of the voltage value of the source. It is also the discharge time if we were discharging the capacitance. Should the capacitance in the figure above be 4U7 (4.7 uF) and the resistance was 1M ohms (one meg-ohm or 1,000,000 ohms) then the time constant would be T = R X C = [1,000,000 X 0.000,0047] = 4.7 seconds. These properties are taken advantage of in crude non critical timing circuits.

Capacitors in series and parallel

Capacitors in parallel ADD together as C1 + C2 + C3 + ..... While capacitors in series REDUCE by:

1 / (1 / C1 + 1 / C2 + 1 / C3 + .....)

Consider three capacitors of 10, 22, and 47 uF respectively.

Added in parallel we get 10 + 22 + 47 = 79 uF. While in series we would get:

1 / (1 / 10 + 1 / 22 + 1 / 47) = 5.997 uF.

Note that the result is always LESS than the original lowest value.

Simplified calculations for Capacitors

We said above that parallel combinations simply add the values together. Series combinations are somewhat more difficult requiring 1 / (1 / C1 + 1 / C2 + 1 / C3 + ...).

This can be simplified somewhat to:

[(C1 X C2) / (C1 + C2)]

Try three or more in series. Do the first two then arrive at an intermediate value, then do the third with the intermediate value and so on.

What is even more difficult is if you need to use a series combination to get down from a known value capacitor to a desired net value of capacitance. In that case use this formula:

[(C1 X C2) / (C1 - C2)]

As one example, if you have a 220 pF fixed capacitor but need a net value of about 68 pF:

[(220 X 68) / (220 - 68)] = 98.4 pF (use 100 pF)

Again try three or more in series. Do the first two then arrive at an intermediate value, then do the third with the intermediate value and so on.

Remember low value capacitors are 5% tolerance and higher values are likely 10% so don't get too paranoid with precision calculations. As an exercise play around with 18 pF ±5% tolerance and 82 pF ±10% tolerance using both extreme ends of tolerance as well as their nominal values. When we come to electrolytic capacitors the tolerance is often + 80% / - 20% and require a DC polarization. Helps to keep things in a proper perspective.

Figure 2. - capacitors in series and in parallel

A very important property of Capacitors

Capacitors will pass AC currents but not DC. Throughout electronic circuits this very important property is taken advantage of to pass ac or rf signals from one stage to another while blocking any DC component from the previous stage.

Figure 3 - capacitors passing ac blocking dc

What do capacitors look like?

In figure 4 we have a photo of a selection of fixed and variable capacitors. The upper capacitor is a variable capacitor. Down the left hand side we have a number of electolytic capacitors.

Figure 4 - a selection of fixed and variable capacitors

The red capacitor in the lower left is a tag tantalum type of greater tolerance and high stability. The yellow is a metallised polypropylene film type while the green ones at the right are the popular polyester types "Greencaps".

In the middle are silver mica capacitors which I personally think are somewhat over rated although these were 1% tolerance types. At the upper right is a 25 pF beehive trimmer.

Should your budget allow, consider building an LC meter kit to be able to measure either the inductance of your chokes, inductors or even check the capacitance of capacitors.

BOOK - Capacitor Handbook by Cletus J. Kaiser

SOURCE: http://www.electronics-tutorials.com/basics/capacitance.htm

2009-01-19T02:55:00.000-08:00

VOLTAGE

What is voltage?

Voltage should be more correctly called "potential difference". It is actually the electron moving force in electricity (emf) and the potential difference is responsible for the pushing and pulling of electrons or electric current through a circuit.

Sources of electromotive force (EMF) or voltage

To produce a drift of electrons, or electric current, along a wire it is necessary that there be a difference in "pressure" or potential between the two ends of the wire. This potential difference can be produced by connecting a source of electrical potential to the ends of the wire.

As I will explain later, there is an excess of electrons at the negative terminal of a battery and a deficiency of electrons at the positive terminal, due to chemical action.

Then it can be seen that a potential difference is the result of the difference in the number of electrons between the terminals. The force or pressure due to a potential difference is termed e.m.f. or voltage.
See: electron theory

An emf also exists between two objects whenever there is a difference in the number of free electrons per unit volume of the object. If the two objects are both negative, current will flow from the more negatively charged to the less negatively charged when they are connected together. There will also be an electron flow from a less positively charged object to a more positively charged object.

The electrostatic field, i.e. the strain of the electrons trying to reach a positive charge or from a more highly negative charge is emf or voltage.

It is expressed in units called volts, short for voltage. A volt can be defined as the pressure required to force a current of one ampere through a resistance of one ohm.

To make this easier to visualise, consider the water pressure (voltage) required to pass a litre of water (current) through a copper pipe of a certain small diameter (resistance).

Also try and visualise water going through other pipes of varying diameters (smaller to larger in size). Either the water pressure required would vary or the volume delivered would vary, or both.

You have just grasped the basics of ohms law, where E = voltage; I = current in amperes and R = reistance in ohms:

This voltage can be generated in many different ways

Some examples:

Chemical (batteries) e.g. dry cell 1.5V, wet cell storage about 2.1V

Electromagnetic (generators)

Thermal (heating junctions of dis-similar metals)

Piezoelectric (mechanical vibration of certain crystals)

Photoelectric (light sensitive cells)

A simple experiment in voltage

Yet to be completed as soon as I find a simple, inexpensive way for people to make measurements.

SOURCE: http://www.electronics-tutorials.com/basics/voltage.htm

2009-01-19T02:52:00.000-08:00

CURRENT

What is current?

A flow of electrons forced into motion by voltage is known as current. The atoms in good conductors such as copper wire have one or more free electrons of the outer ring constantly flying off. Electrons from other nearby atoms fill in the holes. There are billions of electrons moving aimlessly in all directions, all the time in conductors.

When an emf (voltage) is impressed across a conductor it drives these free electrons away from the negative force toward the positive. This action takes place at near the speed of light, 300,000,000 metres per second although individual electrons do not move far they have a shunting effect. This is similar to a number of cars pulled up at traffic lights when the last vehicle fails to stop and hits the second last vehicle which in turn hits the third last vehicle...............

The amount of current in a circuit is measured in amperes (amps). Smaller units used in electronics are milli-amps mA (1 / 1,000th of an ampere) and micro-amps uA (1 / 1,000,000th of an ampere). An ampere is the number of electrons going past a certain point in one second.

The quantity of electrons used in determining an ampere is called "coulomb" which one ampere is one coulomb per second. A coulomb is 6,280,000,000,000,000,000 or 6.28 X 10 ¹⁸ electrons.

This (a coulomb) is the unit of measuring electrical quantity or charge.

SOURCE: http://www.electronics-tutorials.com/basics/current.htm

2009-01-19T02:47:00.000-08:00

OHMS LAW

Why is ohms law so very important?

Ohms law, sometimes more correctly called Ohm's Law, named after Mr. Georg Ohm, mathematician and physicist b. 1789 d. 1854 - Bavaria, defines the relationship between power, voltage, current and resistance. These are the very basic electrical units we work with. The principles apply to a.c., d.c. or r.f. (radio frequency).

Ohms Law is the a foundation stone of electronics and electricity. These formulae are very easy to learn and are used extensively throughout our tutorials. Without a thorough understanding of "ohms law" you will not get very far either in design or in troubleshooting even the simplest of electronic or electrical circuits.

Would you believe I receive email from fools who assert "all this mathematical rubbish over ohms law is totally unecessary" - actually I've 'cleaned' that up a bit. They are the true non-believers, the guaranteed non-achievers of the future.

Mr. Ohm (that is his 'real'name) [Georg Ohm b 1789 d 1854 - Bavaria] established in the late 1820's that if a voltage [later found to be either A.C., D.C. or R.F.] was applied to a resistance current would flow and then power would be consumed". then "

Some practical every day examples of this very basic rule are:

Radiators (electric fires), Electric Frypans, Toasters, Irons and electric light bulbs.

Figure 1 - ohms law power consumption through a resistance

The radiator consumes power producing heat for warmth, the frypan consumes power producing heat for general cooking, the toaster consumes power producing heat for cooking toast, the iron consumes power producing heat for ironing our clothes and the electric light bulb consumes power producing heat and more important light for lighting up an area. A further example is an electric hot water system. All are examples of ohms law at its most basic.

Hot and Cold Resistance encountered in Ohms Law

One VERY important point to observe with ohms law in dealing with some of those examples is that quite often there are two types of resistance values. "Cold Resistance" as would be measured by an ohm-meter or digital multimeter and a "Hot Resistance". The latter is a phenomenem of the material used for forming the the resistance itself, it has a temperature co-efficient which often once heated alters the initial resistance value, usually dramatically upward.

A very good working example of this is an electric light bulb. "what may be termed a bright idea " .

I just measured the first light bulb with my digital multimeter. It showed zero resistance, in fact open circuit. That's what you get, when for safety reasons you put a burnt out bulb back into an empty packet and a "neat and tidy" wife puts it back into the cupboard. .

O.K. here's a "goodie" and, it's labelled "240V - 60W", it measured an initial "cold resistance" of 73.2 ohms. Then I measured our actual voltage at a power point as being 243.9V A.C. at the moment [note: voltages vary widely during a day due to locations and loads - remember that fact - also for pure resistances, the principles apply equally to A.C. or D.C.].

Using the formula which you will learn below, the resistance for power consumed should be R = E² / P OR R = 243.9² / 60W = 991 ohms

That is 991 ohms calculated compared to an initial reading of 73.2 ohms with a digital multimeter? The reason? The "hot" resistance is always at least ten times the "cold" resistance.

Now through our "Electronics Q&A" I asked people around the world to perform similar measurements for me. The results were substantially the same even allowing for the different AC voltage levels in different countries.

Another example is what is most often the biggest consumer of power in the average home. The "electric jug", "electric kettle" or what ever it is called in your part of the world. Most people are astonished by that news. My "electric kettle" is labelled as "230 - 240V 2200W". Yes 2,200 watts! That is why it boils water so quickly. [As a former plumber among my many qualifications, I could give you the formula of power required to boil water in a certain space of time, but I won't - alright, it's at the VERY, VERY bottom of this page.]

What are the ohms law formulas?

To make it much easier for you I have put all the relevent formulas together for you here complete with worked examples of ohms law. You will notice the formulas share a common algebraic relationship with one another.

For the worked examples voltage is E and we have assigned a value of 12V, Current is I and is 2 amperes while resistance is R of 6 ohms. Note that "*" means multiply by, while "/" means divide by.

For voltage [E = I * R] E (volts) = I (current) * R (resistance) OR 12 volts = 2 amperes * 6 ohms

For current [I = E / R] I (current) = E (volts) / R (resistance) OR 2 amperes = 12 volts / 6 ohms

For resistance [R = E / I] R (resistance) = E (volts) / I (current) OR 6 ohms = 12 volts / 2 amperes

Notice how simple it is?

Now let's calculate power using the same examples.

For power P = E² / R OR Power = 24 watts = 12² volts / 6 ohms

Also P = I² * R OR Power = 24 watts = 2² amperes * 6 ohms

Also P = E * I OR Power = 24 watts = 12 volts * 2 amperes

That's all you need for ohms law - remember just two formulas:

for voltage E = I * R and;

for power P = E² / R

You can always determine the other formulas with elementary algebra.

Ohms law is the very foundation stone of electronics!

Knowing two quantities in ohms law will always reveal the third value. I suggest you print these formulas out and paste them onto scrap cardboard to keep your ohms law as a handy reference until you are quite familiar with it.

If you prefer I've added [2nd May, 2001] a graphical representation here in figure 2.

See further below for related topics and links including FREE downloads.

Figure 2 - ohms law graphical chart

SOURCE: http://www.electronics-tutorials.com/basics/ohms-law.htm

2009-01-19T02:42:00.000-08:00

RESISTANCE

What is resistance?

In the topic current we learnt that certain materials such as copper have many free electrons. Other materials have fewer free electrons and substances such as glass, rubber, mica have practically no free electron movement therefore making good insulators. Between the extremes of good conductors such as silver, copper and good insulators such as glass and rubber lay other conductors of reduced conducting ability, they "resist" the flow of electrons hence the term resistance.

The specific resistance of a conductor is the number of ohms in a 1' (305mm) long 0.001" dia round wire of that material.

Some examples on that basis are Silver = 9.75 ohms, Copper = 10.55 ohms, Nickel = 53.0 ohms and Nichrome = 660 ohms

From this information we can deduce that for a voltage applied to a piece of Nichrome wire , only around 10.55 / 660 = 0.016 of the amount of current will flow as opposed to the the current flowing in the same size copper wire.

The unit of resistance is the ohm and 1 ohm is considered the resistance of round copper wire, 0.001" diameter, 0.88" (22.35 mm) long at 32 deg F (0 deg C).

Resistance in series and parallel

It follows if two such pieces of wire were connected end to end (in series) then the resistance would be doubled, on the other hand if they were placed side by side (in parallel) then the resistance would be halved!

This is a most important lesson about resistance. Resistors in series add together as R1 + R2 + R3 + ..... While resistors in parallel reduce by 1 / (1 / R1 + 1 / R2 + 1 / R3 + .....)

Consider three resistors of 10, 22, and 47 ohms respectively. Added in series we get 10 + 22 + 47 = 79 ohms. While in parallel we would get 1 / (1 / 10 + 1 / 22 + 1 / 47) = 5.997 ohms.

Resistance and Power

Next we need to consider the power handling capability of our resistors. Resistors which are deliberately designed to handle and radiate large amounts of power are electric cooktops, ovens, radiators, electric jugs and toasters. These are all made to take advantage of power handling capabilities of certain materials.

From our topic on ohms law we learnt that P = I * I * R that is, power equals the current squared times the resistance. Consider our example above of the three resistors in series providing a total resistance of 79 ohms. If these resistors were placed across a 24 volt power supply then the amount of current flowing, from ohms law, is I = E / R = 24 / 79 = 0.304 amperes.

Using any of our power formulas we determine that 0.304 amperes flowing through our 79 ohm resistance dissipates a combined 7.3 watts of power! Worse, because our resistors are of unequal value the power distribution will be unequal with the greater dissipation in the largest resistor.

It follows as a fundamental rule in using resistors in electronic circuits that the resistor must be able to comfortably handle the power it will dissipate. A rule of thumb is to use a wattage rating of at least twice the expected dissipation.

Common resistors in use in electronics today come in power ratings of 0.25W, 0.5W, 1W and 5W. Other special types are available to order. Because of precision manufacturing processes it is possible to obtain resistors in the lower wattage ratings which are quite close in tolerance of their designated values. Typical of this type are the .25W range which exhibit a tolerance of plus / minus 2% of the value.

Resistors come in a range of values but the two most common are the E12 and E24 series. The E12 series comes in twelve values for every decade. The E24 series comes in twenty four values per decade.

E12 series - 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82

E24 series - 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91

You will notice with the E12 values that each succeeding value falls within the plus / minus 10% of the previous values. This stems from the real old days when resistances were stated as within 20% tolerance (accuracy). Later values of plus / minus 5% tolerance led to the E24 range of resistance. Quite common today are 2% tolerance metal films types but for general purpose use we tend to stick to E12 values of resistance in either 1%, 2% or 5% tolerance.

Cost is the determining factor and many retailers now stock the 2% range of resistance as a standard to minimise stocking levels and also at reasonably low cost.

As examples of say the "22" types (red - red) from the E12 series we get 0.22, 2.2, 22, 220, 2,200, 22,000, 220,000 and 2,200,000 or eight decades of resistors.

In my opinion these ought to be referred to respectively as R22, 2R2, 22R, 220R, 2K2, 22K, 220K and 2M2. Here the R, K and M hold places where no decimal points are used to cause confusion.

Consider if I meant to write (in the old fashioned way) 2.2K in for a circuit value but forgot to type in the "K" so you just had 2.2, would the circuit work? No! How easy is it for you to read decimal points above.

Isn't 2K2 easier to see as meaning 2,200 ohms as against 2.2K? What if you didn't see the decimal point in 2.2K, couldn't it be taken to mean 22K or 22,000 ohms? Now you know why I prefer to use 2K2 or 22K or 22R - no confusion.

Resistance colour chart codes

Here in this large colour chart is the resistance colour code - learn the sequence forever -

BLACK, BROWN, RED, ORANGE, YELLOW, GREEN, BLUE, PURPLE, SILVER, WHITE

I have accommodated two current colour banding of resistances - four band and five band resistance colour code. It should be pretty self explanatory I hope.

The five band code is more likely to be associated with the more precision 1% and 2% types. Your "garden variety" 5% general purpose types will be four band resistance codes.

BOOK - The Resistor Handbook by Cletus J. Kaiser

SOURCE : http://www.electronics-tutorials.com/basics/resistance.htm

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1990-10-04T22:10:00.000-07:00

Electronic Tutorials

ELECTRONIC TUTORIAL AND ARTICLE

Atoms and electrons

Electron Theory and Metals

Alloys

Decoder/Demultiplexer

Priority Encoder

T flip flop

The D Latch and the D flip-flop

SR Bistable Switch Debounce Circuit

Switch Debounce Circuits

SR Bistable Switch Debounce Circuit

Gated or Clocked SR Flip-Flop

SR Flip-Flop

The SR NAND Gate Latch

The Set State

Reset State

Truth Table for this Set-Reset Function

The NOR Gate SR Flip-flop

4000 series CMOS Logic ICs

Quad 2-input gates

Triple 3-input gates

Dual 4-input gates

4068 8-input NAND/AND* gate

4069 hex NOT (inverting buffer)

4049 hex NOT and 4050 hex buffer

4000 dual 3-input NOR gate and NOT gate

Decade and 4-bit Counters

4017 decade counter (1-of-10)

4026 decade counter and 7-segment display driver

4029 up/down synchronous counter with preset

4510 up/down decade (0-9) counter with preset4516 up/down 4-bit (0-15) counter with preset

4518 dual decade (0-9) counter4520 dual 4-bit (0-15) counter

7-bit, 12-bit and 14-bit counters

4020 14-bit (÷16,384) ripple counter

4024 7-bit (÷128) ripple counter

4040 12-bit (÷4096) ripple counter

4060 14-bit (÷16,384) ripple counter with internal oscillator

Decoders

4028 BCD to decimal (1 of 10) decoder

7-segment Display Drivers

4511 BCD to 7-segment display driver

Logic gate

AUDIO TRANSFORMERS

What are audio transformers?

Primary impedance of audio transformers

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TRANSFORMERS

What are transformers?

Power transformers

Audio transformers

RF transformers

TRANSISTORS

Introduction to transistors?

History of Transistors

How do transistors work?

How do holes and electrons conduct in transistors?

Transistor amplification

The NPN transistor

Historical Footnote on Transistors - [added 1st May, 2000]

FET's as transistors

How are semiconductors made?

DIODES

What are Diodes?

Schematic symbols for Diodes

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Rectifying Diodes

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Diodes as frequency multipliers

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Switching Diodes in Logic Circuits

Light-Emitting-Diodes or LED's

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IMPEDANCE

What is impedance?

A simple example of impedance

High Impedance loads and Low Impedance loads

General expression of Impedance

4510 up/down decade (0-9) counter with preset
4516 up/down 4-bit (0-15) counter with preset

4518 dual decade (0-9) counter
4520 dual 4-bit (0-15) counter