A venture in retrotronics

5V daylight intensity sensor, for direct connection to AD converter of microcontroller

This little module requires only power (5V), and provides a voltage between 0V and 4.2V, depending on the intensity of the light falling onto the photodiode sensor. It can be connected directly to an analog-digital converter of a microprocessor for readout, requiring no further logic.

The four pins are positioned in such a way that the module can be inserted in a standard (2.54mm hole-to-hole) breadboard for experimenting.


  • 5V power
  • 0-4.2V output; can be connected directly to an ADC of a microprocessor
  • built around photodiode and opamp; no LDR involved, i.e. no cadmium
  • ready for insertion in a standard (2.54mm hole-to-hole) breadboard
  • board size only 14x15mm
  • high-quality PCB, designed in KiCad, and produced by Aisler (Germany), PCBWay (China) and OSH Park (USA)
  • board comes fully assembled and tested

NOTE: this module is 5V only, and cannot be used with a 3.3V power supply.


I've created this module as a modern alternative to the traditional voltage divider circuits based on photoresistors (i.e. LDR's containing cadmium). Unfortunately, photodiodes (just like photo transistors) provide only a small current when light is falling onto the silicon (they are basically tiny solar cells), so they need an operational amplifier (opamp) before the output can be delivered to an AD converter for readout.

This module provides the photodiode, the opamp and its feedback circuitry in a single package, ready for use.

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