ELECTRONICS TECHNIQUES
As discussed in the previous blog, electronics is much like baking. So, the following list are some the ingredients needed to build electronic projects. Only four components and their sub-catagories will be listed for now. The rest I will cover in successive blogs.
1) Resistors
- Carbon resistors
- Wire wound resistors
- Potentiometers
- Precision Resistors
- Thick film Resistors
2) Capacitors
- Electrolytic Capacitors
- Polarised capacitor
- Non-polarised Capacitors
- Tantalum Capacitors
- Ceramic Capacitors
- Surface mounted resistors
3) Diodes
- Silicon Diodes
- Rectifiers
- Bridge rectifiers
- Selenium rectifiers
- Variac Diodes
- Zenner Diodes
- Surface mounted Diodes
4) Transistors
- Signal Transistors
- Power transistors
- Surface mounted Diodes
Today I'm going to chat about resistors. The thing that impresses people the most about an electronic circuit board is the power resistor, I suppose because they add colour to the electronic board and because of the function they do, even if they look a bit discolored and burnt at times. However, resistors are little carbon rods with metallic caps attached at either end, to which a segment of wire is attached. See pic below. These metal ends caps and wire segments are often made of copper and is tin plated. Resistors come in various sizes and its size classifies its wattage... how much heat it is capable of dissipating and remain in one piece and leave the colour bands recognisable. Resistors are made as 1/8 watt, 1/4 watt, 1/2 watt, 1 watt and 2 watt but when they become larger than this, they are not commonly made of carbon but rather of high resistive wire like, tungsten or nichrome wrapped around asbestos rope and embedded in ceramic. There are huge 100 Watt and greater resistors around. But more about that later.
I suppose you also wondering what this Watt things is, well the short explanation, heat is measured in Watts per hour. Think electric bulb...., 60 Watt globes / 100 Watt globes, their filaments resists current flow which causes their filaments to glow giving light and as a consequence, give off heat, meaning these bulbs will dissipate 60, / 100 watts of heat over a period of an hour respectively. Our little resistors do the same, they resist current flow but the heat they generate on circuit boards are hardly enough to be felt if you placed your finger on it.
These carbon resistors do exactly what its name implies, - they resist electricity. But each resistor of a different value exhibits a different resistance. This resistance is measured in ohms. For now, just accept that the ohm is a measurement. For example, the gram/ Kg is the measure of weight or the meter / kilometer is the measure of distance. Likewise, the ohm is the measure of resistance and is depicted by the Omega sign, Ω.
So to get back to those colourful beauties. Let me tell you about the colours, its in fact a code. A code known by all electronics engineers and their apprentices, so in order for you to become efficient at electronics to any degree, you need to know the code. Its essential! Its quite simple though, and each colour has a number it represents. The reason for this, writing text on these tinys are a bit problematic besides when they heat up and the inked text changes colour, it become indistinguishable. Anyway, there are precision resistors (1% tolerance) that have text values written on them but are used for specific and special electronic designs. We are more interested in the garden variety resistor for now, but will bet back to precision resistors in a later blog. Resistors are passive devices, meaning they do not do any electronic switching like transistors or thyristors do. (If unclear, I will explain later)
THE CODE
The colours are as follows:-
- Black = 0
- Brown= 1
- Red = 2
- Orange = 3
- Yellow = 4
- Green = 5
- Blue = 6
- Violet = 7
- Grey = 8
- White = 9
This is the numerical system used for resistors much like the number system we use for money... tens and units. Resistor code starts with 0 and ends at 9 which is still ten units. However there are two additional colours viz. gold and silver. But we will deal with these in greater depth later.
Commonly you will find a resistor with four colour lines perpendicular to its length, one could say its a ring of colour as it goes all the way around its small carbon body. (See Pic above) These lines are not equidistant along the resistor's body but tend to be more positioned towards one end. This is the end from which we read the code.
These colour bands are not all born equal. The first two is used to define the resistor value, for example if the first two bands were red and red, we give it a number of 22. Like wise if the colour bands were brown and black its number would be 10. However, these numbers described by the first two colour bands is subject to the colour of the third band which is called the multiplier. (Or the amount of noughts it represents) For example if the first 3 bands were all red, we would have 22 as previously explained but the third red band represents the number of noughts. So 22 would have 2 noughts behind it (22 00) meaning that resistor is 2200 Ohms, alternatively it can be written as 2.2k ohms (2.2 thousand ohms).
Another example is brown and black as the first two colour bands and black as a third, implying 10 with 0 noughts which then remains 10 ohms. If that third band was brown instead, it would have meant 1 nought, thus the resistor would be 100 ohms, if it was red, the resistor would be a 1000 ohms or 1K ohm. A third example just for luck. First and second bands both orange and a third yellow implying 33 flanked by 4 noughts making that resistor 330000 ohms, alternatively 330K Ohms. Most of the time we drop the word "Ohm" and just say k. Like its a 22k or a 7.4k or a 10k. I'm certain you've got it by now. If not, give me some feedback.
Commonly you will find a resistor with four colour lines perpendicular to its length, one could say its a ring of colour as it goes all the way around its small carbon body. (See Pic above) These lines are not equidistant along the resistor's body but tend to be more positioned towards one end. This is the end from which we read the code.
These colour bands are not all born equal. The first two is used to define the resistor value, for example if the first two bands were red and red, we give it a number of 22. Like wise if the colour bands were brown and black its number would be 10. However, these numbers described by the first two colour bands is subject to the colour of the third band which is called the multiplier. (Or the amount of noughts it represents) For example if the first 3 bands were all red, we would have 22 as previously explained but the third red band represents the number of noughts. So 22 would have 2 noughts behind it (22 00) meaning that resistor is 2200 Ohms, alternatively it can be written as 2.2k ohms (2.2 thousand ohms).
Another example is brown and black as the first two colour bands and black as a third, implying 10 with 0 noughts which then remains 10 ohms. If that third band was brown instead, it would have meant 1 nought, thus the resistor would be 100 ohms, if it was red, the resistor would be a 1000 ohms or 1K ohm. A third example just for luck. First and second bands both orange and a third yellow implying 33 flanked by 4 noughts making that resistor 330000 ohms, alternatively 330K Ohms. Most of the time we drop the word "Ohm" and just say k. Like its a 22k or a 7.4k or a 10k. I'm certain you've got it by now. If not, give me some feedback.
THE TOLERANCE BAND
The forth band is called the tolerance band, most commonly gold or silver. If its gold it implies 5% tolerance, meaning if a resistor is marked as 100 ohms it could vary between 95 ohms and 105 ohms. But please understand vary does not mean constant variation. Restated, if a batch of 10 resistors were manufactured, 2 could be 96 Ω (fixed) 4 could be 102 Ω (fixed), 1 could be 100 Ω (fixed) and the other three, each 104 Ω (fixed). Get the picture? If this fourth colour band was silver instead of gold, it would have a tolerance of 10%. So finally, we have a resistor with bands red, violet, red, and gold which would be a 2700 ohms or 2.7k Ω with a 5% tolerance. And that it! Resistors come in a variable type as well but they are called potentiometers and have three legs (connectors) rather than 2.
Bare in mind many resistors have a base colour, for arguments sake, beige. It would then have its colour bands painted on a beige base colour. A quick way to remember the code, is by learning the following:-
Black Boys Rape Our Young Girls But Violet Gives Willingly. Please understand that all electronics engineers are not perverts, neither is this meant to be prejudice statement, its just a memory jogger. Next up we cover capacitors but first a general discussion about electronics would be in justified to raise your interest in the subject.
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