IR Proximity sensor

In this original design the main component is an OPIC (optical IC) from SHARP (IS471F). It is a very handy component that has everything inside it for detecting reflected IR-light. It has a build-in modulator and detector. So you only need a few extra components (a resistor and a IR-LED) to get a complete working detector.

The resistor sets the power of the IR-LED and hence the threshold of the detector. The output of the OPIC is about Vcc V when light is detected, otherwise it is about 0 V.

IS471F

Remark: instead of using 6 small diodes, I use a small round bridge-rectifier and two extra diodes.

As in my other designs, I did not use a PCB to mount everything on. I just soldered everything together in order to get a real compact circuit which fitted into one 2 x 4 brick. I hollowed out the brick and drilled one big hole at the right of the front for the IR-LED. At the left side of the front I drilled four small holes where I could stick the leads of the OPIC through.

To use this sensor you only have to set the sensor input type on the RCX to a light sensor input. It will give you a reading of 0 when no light is reflected and 100 when an object is detected. Using a 220 ohm resistor my sensor reacts at a distance of about 2,5 to 5 cm, depending on the material the light is reflected on.