Resistors
Resistors are a basic fundamental component of electronics. Their purpose is to resist (effectively limiting) current and come in varying sizes.
How Resistors Are Made
The common carbon composition resistors have a carbon composition inside with a protective housing on the outside, also with wire lead leading in and out - to carry the current in and out. Carbon composition is a powdered carbon mixed with a glue-like binder. The resistance can be changed from one resistor to the next by changing the ratio of carbon to the binder.
Color Codes
| Color | Band 1 | Band 2 | Band 3 (Multiplier) |
|---|---|---|---|
| Black | 0 | 0 | 1 |
| Brown | 1 | 1 | 10 |
| Red | 2 | 2 | 100 |
| Orange | 3 | 3 | 1,000 |
| Yellow | 4 | 4 | 10,000 |
| Green | 5 | 5 | 100,000 |
| Blue | 6 | 6 | 1,000,000 |
| Violet | 7 | 7 | 10,000,000 |
| Gray | 8 | 8 | 100,000,000 |
| White | 9 | 9 | - |
N.B.There is sometimes a fourth band indicating the tolerance of the resistor. Gold = ± 5%, Silver = ± 10% and no band = ± 20%.
Types of Resistors
There are many different types of electronic resistors:
- Metal Film Resistors - These use a thin film of metal (or use a metal particle mixture) so different resistances can be realised.
- Carbon Film Resistors - These have a carbon film on a tiny ceramic cylinder. The resistance is controlled by a spiral groove that is cut into the film so the length of carbon can be changed between resistors.
- Wire-wound Resistors - These resistors have a tubular form and are wrapped with coils of resistance wire. These are very precise and take lots of heat.
- Variable Resistors - Sometimes known as Potentiometers, this is a generic term for resistors where their resistance can be changed manually. These are used in filters, radio - for changing volume, lamps for changing brightness etc.
- Photoresistors - Photoresistors (or photocells) are made from a light-sensitive material (possibly cadmium sulfide) and are variable resistors, by decreasing the light level, increases the resistance and vice versa.
- Thermistors - Again, these are variable resistors where increasing the temperature will decrease their resistance.