Types of Electronic Components
All electronic circuits have some sort of resistor in them. Simple resistors of various sizes are used to vary current, split current, and reduce voltage levels to those appropriate for a particular application. Other resistors such as variable resistors and light-dependent resistors (LDRs) can also be used for advanced circuits.
Here are just a few things that resistors can do:
- Divide voltages for delivering the appropriate voltage to electronic components, especially transistors, so the component will operate properly.
- Limit the current in a circuit so a particular component isn't damaged. Again, this is particularly important with transistors, which will "burn up" or fail sooner than necessary if they are drawing too much current.
- Bleed off a charge from a capacitor in a unit being repaired or serviced so the operation can be conducted safely.
- Dissipate power as a dummy load to test circuits; for example, a resistor can be used in the place of an antenna for a transmitter for testing purposes.
Because fixed resistors are very small, a standard labeling method exists for determining a resistor's value. The value in ohms is based on the colors of the bands on the resistor. The colors can be remembered by recalling the color spectrum "ROY G. BiV" and adding black, brown, gray and white to the ends. There can be four to six bands on the resistor; the last two bands indicate a multiplier and tolerance value. For example, for four bands, the first two bands read from left to right indicate value and the third band indicates number of zeros:
- Black: 0/0/0 (tens)
- Brown: 1/1/1 (hundreds)
- Red: 2/2/2 (thousands)
- Orange: 3/3/3 (ten thousands)
- Yellow: 4/4/4 (hundred thousands)
- Green: 5/5/5 (millions)
- Blue: 6/6/6 (ten millions)
- Violet: 7/7/not used
- Gray: 8/8/not used
- White: 9/9/not used
The fourth band indicates the resistor's tolerance; for example, gold indicates the accuracy is +/-5%.
Sometimes, fixed resistors won't get the job done. Circuits to dim lights or adjust speaker volume and circuits that react to a lack of light for turning something on or off (e.g., outdoor lights or an alarm system) need something more versatile.
Potentiometers are commonly used to provide a variable resistance when needed. Usually a potentiometer is formed by bending a resistive strip into a circle and connecting terminals to each end; this provides the typical knob used in most applications. However, a strip may also be used, such as those widely found in the slides used in the music industry.
LDRs are widely used to automatically turn on lights when it gets dark. Common applications are outdoor lighting in residences and commercial buildings as well as headlights on automobiles. Light-dependent resistors are so small that they are typically not labeled; the maximum resistance of an LDR can be found by measuring it in the dark.
Excellent presentation on Resistors
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