Potentiometer

Potentiometers are used in circuits, when it is necessary to alter the resistance. Dark/light and temperature sensors usually have these components, as the potentiometer / variable resistor allows the circuit to be made more or less sensitive (they can be turned up or down - reducing or increasing resistance).

The long handle on the potentiometer / variable resistor can be turned clockwise or anticlockwise, altering the value of the resistance. The range of resistance varies, for example: 0 to 100 ohms 0 to 1M ohms

This can be seen when using circuit simulation software such as Circuit Wizard. The resistance value of a potentiometer / variable resistor can be altered. The animations starts with a 4.67% resistance level and reaches a resistance level of 28.33%. It can go all the way up to 100% resistance, preventing current flow, in a circuit. The resistance is altered by using the computer’s mouse, to turn the potentiometer’s dial.

The circuit below is a temperature sensor. When the temperature drops below 3 degrees centigrade, an LED illuminates. Increasing the resistance value of the potentiometer / variable resistor, by turning its handle, makes the circuit less sensitive. For instance, the temperature sensor would require a higher temperature (e.g. 8 degrees centigrade) before the LED illuminates. Circuit explanation in detail: When the thermistor is warmed up by an hair drier its resistance drops, this will take a few seconds. As its resistance drops current begins to flow from positive 9volts to negative 0 volts. Current flows into the base of the transistors allowing the LED to light. The handle of the potentiometer / variable resistor can be turned up or down, to increase or decrease resistance, in this way it can make the circuit more or less sensitive.

For more details : Potentiometer