Variable resistors have a predetermined range of resistance that can be adjusted manually or automatically. All variable resistors are non-polarized.

Function

Variable resistors limit current and divide voltage.

Operating Values

There are three ratings:

1. Maximum resistance measured in Ohms Ω
2. Power rating measured in Watts
3. Voltage rating measured in Volts

The power rating defines the maximum amount of current the resistor can handle. The voltage rating defines the maximum amount of voltage the resistor can handle.

Flex Sensors

Increases resistance when bent in one direction

Photocell

Varies resistance in response to light levels. They typically decrease resistance as light levels increase.

Potentiometers

A potentiometer is a variable resistors with three terminals. The outer two terminals have a fixed resistance between them, from 0 to the maximum predefined resistance. The middle terminal is connected to the wiper, which varies the resistance. The most common type of potentiometer, or pot, is the Rotary Pot, which has a knob attached to it. Another type of pot is the trimpot or trimmer. Trimpots are typically used to calbrate the resistance needed in a circuit.

Thermistors

Temperature sensitive variable resistors convert temperature change to a change in resistance. There are two kinds of thermistors:

1. One that increases in resistance with an increase in temperature
2. One that decreases resistance with an increase in temperature.