RESISTORS 1). What is a resistor ? 2). How to read a resistor 3). Colour codes 4). Resistor types 5). Resistors in Series *************************************************************************** 1). What is a resistor ? Basically it is a small piece of carbon with a metal leg at each end. The small amount of carbon gives a certain value according to size, a value could well be :- 1k or 10k or 1 Meg see more of the values in '4' and see IFF 1 Also, Resistors are used to cut down the flow of current in circuits. The Resistance is measured in Ohms, in actual fact a resistor can vary from a few Ohms to Millions. You can get variouse sorts, like small 1/4 watt to wire wound or perhaps larger ceramic. *************************************************************************** 2). How to read a resistor. Well first, if you look at the IFF picture in 'IFF 2' you will find a more detailed idea of what I mean. But how to do this is quite easy, pick up any resistor and look for a Silver or Gold ring at the one end. Firstly you will see three coloured rings and then a space and then the silver or gold ring at the other end. The three coloured rings or maybe you want to call them bands instead, could be any colour, but we will say Red, Red, Black which by the way is 22 Ohms and then at the far end happens to be a Silver band. DO NOT READ from the Silver or Gold band end but instead you MUST ALWAYS read from the first coloured band furthest away from the Silver or Gold band. If you are not sure about things like K and Meg then K=1000 Ohms and 1 Meg = 1000,000 Ohms so a Resistor of 1k is 1000 and one which reads 10 Meg is actually Ten Million. You may also see a value perhaps in a book or magazine like eg:- 4k7 or 4.7k Ohms this simply means 4k7 is the same as 4.7k which is 4 thousand and 7 hundred Ohms. Now a bit about the Silver, Gold and Red band or what is known as the tolerance band (the fourth band). Silver = 10%, Gold = 5% and Red = 2% so if we had a value of 1k with a Silver band then the Resistor value would be between 1010 Ohms or 990 Ohms + or - 10%. See what I mean ? If it is a Gold band then if the value is 1k then it would be 1005 Ohms or 995 Ohms + or - 5% and if it happens to be a Red band then it's + or - 2%. There is also something called the 'E' series but that is not covered here on this disk. But if this sort of Resistor is needed then try looking in a 'Maplin catalogue' for more information. You can get a Resistor colour code card from 'Maplin Electronics' or from any 'Tandy' electronic store, they do not cost much at all really, something like 75p. *************************************************************************** 3). Colour codes. Here is a list of the resistor colour codes for you to understand. There are three bands which give a value and a fourth band which gives tolerance. A Silver band is 10%, a Gold band is 5% and a Red band is 2%. More often you will either see a Silver or Gold band. So here it is :- _______________________ 1st value | _______________________________ 2nd value | | ____________________________________ Multiplier 3 | Black 0 0 x 1 Brown 1 1 x 10 Red 2 2 x 100 Orange 3 3 x 1000 Yellow 4 4 x 10,000 Green 5 5 x 100,000 Blue 6 6 x 1,000,000 Violet 7 7 x 10,000,000 Grey 8 8 x 100,000,000 White 9 9 - So if you see a resistor that reads Brown,Black,Orange then that would be a value of 10k or ten thousand Ohms. If you read one that gives Yellow,Purple,Black then that would be 47 Ohms. If you look at IFF 3 you will see what I mean. *************************************************************************** 4). Resistor types. There are many different values and different sizes and they go in what is known as 'WATTS'. For example, you would expect to find such values as 1/4 Watt, 1/2 Watt, 1 Watt, 2 Watts and so on. Also of course, the bigger the wattage the bigger the Resistor. But for most home construction purposes you would use 1/2 watt. Do not expect to see every Resistor as the same shape because the bigger the resistor then the shape can change altogether, IFF 4 will show what I mean. Some large resistors can have a metal body with fins on to act as a heat sink to stop the resistor from over-heating. Other Resistors may be bolted to a metal chassis for cooling purposes, but of course this may be only in such things like large power supplies or maybe power amplifiers and other power applications. Now, if you have looked at the different IFF's to get familiar with all that you have read, then you can have a better understanding of the Resistor. *************************************************************************** 5). Resistors in Series. If you need a resitor for the value we will just say 120 Ohms then if that sort of value is not available then try 2 in series example... one at 47 ohms and one at 68 ohms the value is 115 but that is near enough or maybe you want 500 ohms you will never actually get a value of 500 the nearest would be 470 just like 47 or 47000 or 27 ohms or 2.7k for some reason this is the tried and tested method. ..... END .....