| How To: Connecting a Photoresistor |
Last Modified: 2006-07-21
A photoresistor is a sensor whose resistance varies with light intensity. Most decrease in resistance as the light intensity increases. In a typical microcontroller application, this resistance must be converted to a voltage so that an A2D converter can measure it. The easiest way to do this is with a voltage divider circuit.
A voltage divider is just two resistors in series connected between a voltage supply and ground. If R1 is connected to the voltage supply and R2 is connected to ground then the voltage at the junction between the two resistors is:
If R1 is the photoresistor, the voltage will increase with increasing light intensity. If R2 is the photoresistor, the voltage will decrease with increasing light intensity.
Sample Photoresistor Circuit
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