Electrical Schematic Code Diagrams

Electrical Schematic Diagrams

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12v RELAY ON 6V SUPPLY

This circuit allows a 12v relay to operate on a 6v or 9v supply. Most 12v relays need about 12v to "pull-in" but will "hold" on about 6v. The 220u charges via the 2k2 and bottom diode. When an input above 1.5v is applied to the input of the circuit, both transistors are turned ON and the 5v across the electrolytic causes the negative end of the electro to go below the 0v rail by about 4.5v and this puts about 10v across the relay.

Alternatively you can rewind a 12v relay by removing about half the turns.

Join up what is left to the terminals. Replace the turns you took off, by connecting them in parallel with the original half, making sure the turns go the same way around 

LED FLASHER WITH ONE TRANSISTOR

LED FLASHER WITH ONE TRANSISTOR

This is a novel flasher circuit using a single driver transistor that takes its flash-rate from a flashing LED. The flasher in the photo is 3mm. An ordinary LED will not work. 

The flash rate cannot be altered by the brightness of the high-bright white LED can be adjusted by altering the 1k resistor across the 100u electrolytic to 4k7 or 10k. 

The 1k resistor discharges the 100u so that when the transistor turns on, the charging current into the 100u illuminates the white LED. 

If a 10k discharge resistor is used, the 100u is not fully discharged and the LED does not flash as bright. 

All the parts in the photo are in the same places as in the circuit diagram to make it easy to see how the parts are connected. 

AM FM Antenna Booster

AM FM Antenna Booster

This antenna booster circuit can be used to amplify the weak signal received by the antenna. Antenna for AM/FM is usually not tuned for the optimal dimension of 1/4 wavelength, since we prefer small portable size. This untuned antenna has very low gain, so the antenna booster circuit here is very helpful in getting better signal reception. Here is the schematic diagram of the circuit:

Use around 470uH coil for L1 if you use for AM frequency (700kHz-1.5MHz) and use around 20uH for SW or FM receiver. For short wave performance, using this antenna booster, you’ll get a strong signal as we get from a 20-30 feet antenna, with only a standard 18″ telescopic antenna and this booster circuit. The power supply should be bypassed by a 47nF capacitor to ground, at a point that should be chosen as close as possible to L1.

1.5V LED FLASHER CIRCUIT

1.5V LED FLASHER CIRCUIT

1.5V LED FLASHER CIRCUIT

AVERAGE CURRENT = 120uA

PEAK LED CURRENT = 20mA

4mS PULSE  1 FLASHE/SEC

APPROX. 6 MONTHS OPPERATION FROM N-CELL

APPROX. 12 MONTHS OPPERATION FROM AA CELL

DAVID JOHNSON AND ASSOCIATES

MINIATURE LED FLASHING CIRCUIT

1.5 VOLT CIRCUIT

Resistance & Resistor

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.

INDUCTOR

 
 DEFINITION- An inductor is a passive electronic component that storesenergy in the form of a magnetic field. In its simplest form, an inductor consistsof a wire loop or coil. The inductance is directly proportional to the number ofturns in the coil. Inductance also depends on the radius of the coil and on the type of material around which the coil is wound.

For a given coil radius and number of turns, air coresresult in the least inductance. Materials such as wood, glass, and plastic - known as dielectric materials - are essentially the same as air for the purposes of inductor winding. Ferromagnetic substances such as iron, laminated iron, and powdered iron increase the inductance obtainable with a coil having a given number of turns. In some cases, this increase is on the order of thousands of times. The shape of the core is also significant. Toroidal (donut-shaped) cores provide more inductance, for a given core material andnumber of turns, than solenoidal (rod-shaped) cores.

The standard unit of inductance is the henry, abbreviatedH. This is a large unit. More common units are the microhenry, abbreviated µH (1 µH =10-6H) and the millihenry, abbreviated mH (1 mH =10-3 H). Occasionally, the nanohenry (nH) is used (1 nH = 10-9 H).

It is difficult to fabricate inductors onto integratedcircuit (IC) chips. Fortunately, resistors can be substituted for inductors in most microcircuit applications. In some cases, inductance can be simulated by simple electronic circuits using transistors, resistors, and capacitors fabricated onto ICchips.

Inductors are used with capacitors in various wirelesscommunications applications. An inductor connected in series or parallel with a capacitor can provide discrimination against unwanted signals. Large inductors are used in the power supplies of electronic equipment of all types, including computers and their peripherals. In these systems, the inductors help to smooth out the rectified utility AC, providing pure, battery-like DC.