Microcontrollers - Using Potentiometers and Understanding Voltage Dividing (Want some Analog Voltages?)

Microcontrollers - Using Potentiometers and Understanding Voltage Dividing (Want some Analog Voltages?)

Are you looking for a good device to use when testing your Analog to Digital Converter (ADC)? Do you need a variable voltage source, rated between zero volts and the top voltage possible for your circuit? In this video, I'll show how these goals can be reached using a potentiometer. Basically a potentiometer is just a fancy voltage divider, but for the purposes of using them correctly in our circuits, a good understanding of these devices is required.

At its most basic level, a potentiometer is simply a resistor. To verify this you can simply measure the resistance across the two outer leads of a potentiometer with a multi-meter. (Remember to set it for ohms before you make the test though.) The multi-meter will read the total resistance at which the potentiometer is rated, or that for which it was designed. This resistance value will probably not be exact, but it should be very close. The thing that sets a potentiometer apart from a regular resistor however, is the fact that the resistance value can be changed by turning the knob attached to the wiper.

To demonstrate the variable nature of the potentiometer, try reading the resistance from the middle lead (wiper) to the either one of the outer leads. Notice that unless the potentiometer is exactly centered, you won't read the same resistance between the wiper lead and both outer leads. Note that the resistance across one side of the potentiometer will be a portion of the total resistance of the device. Don't move that knob!!Now test the middle lead to the opposite side lead and see what you get. You guessed it--the measurement will be the other portion of the total resistance! If you add those two values, you should get the total resistance of the potentiometer (the first reading you did, between the two outer leads).

Now you have a way to get any voltage that you might need for your system, by using a potentiometer. By grounding one of the two outer pins and applying the positive (+) voltage to the other outside pin, you can tune the potentiometer so that the desired voltage will be available on the middle pin. This will be between about zero volts (ground) and the maximum voltage supplied to the potentiometer from the system. You can also check this on the multi-meter as well--just put one test lead on "ground" and the other lead on the middle pin, and read the voltage across those two points.