Simple circuits for detecting and producing infra-red light

Detector

A simple detector can be constructed from an infra-red phototransistor and an LED in series with a power supply.

The phototransisitor allows current to flow when IR light falls on it, the current flowing is proportional to the intensity of the IR light. We used a Sharp PT480E00000F phototransistor from Rapid Electronics

and a white LED

with a 9V PP3 battery with a battery clip all connected together in a connecting block. All of these parts need to be connected up the correct way round.

Emitter

An infra-red source can be made from an IR LED in series with a resistor and a power source.

We used a high power infra-red source from Rapid Electronics in series with a 33ohm resistor connected to a 3V source using two AA cells in a battery holder. We used a connecting block to connect the parts together. It is important to get the LED the correct way round; the anode needs to connect to the positive more positive part of the circuit.