Raspberry Pi LDR Light Sensor Circuit

The MCP3002 Analog-to-Digital Converter (ADC) integrated circuit (IC), may be used to sense light levels. This is a very simple first circuit worth trying, and requires a light-dependent resistor (LDR) and a fixed resistor (Rf) in a potential divider network configuration.

Usually, when light falls on the LDR, its resistance value drops. Ideally, you need an LDR that is sensitive and provides a range of values such that the voltage at the input channel varies between 0 V and 3.3 V.

If you cannot find a suitable LDR that provides the voltage range, it is possible to replace the fixed resistor Rf with an electrolytic capacitor. The negative terminal of the capacitor connects to the ground of course. The capacitor simply acts as a storage tank to store a small charge, which the input detects.

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