This small PCB implements an IR proximity sensor. An IR LED is pulsed at 40KHz. A reflected IR signal is detected by an IR remote control receiver. When a signal is detected, visible LEDs are turned on.

Assembly Notes

The IR LED and sensor should be mounted in the 12-Oclock and 6-O'clock positions of the plastic ring. Illumination LEDs (wiring notes below) can be installed in the other 4 locations. All the LEDs and the sensor could be secured with RTV silicone caulk ('after everything is working; use tape before then''''). The PCB, battery holder, and sensitivity adjust pot go in the rear piece (cover with electrical tape to avoid shorts).

Visible LEDs should be connected to J2. Pin 1 is 3V power. Pins 3, 4, 5 are three separate outputs from the microcontroller, each of which can sink 40mA. Various series/parallel combinations of LEDs and resistors can be connected, as long as the above current limit is not exceeded.

There is a 500 ohm pot in series with the IR LED which can be used to adjust the sensitivity. It could be replaced with a fixed resistor for the final assembly, or the pot could just be covered with tape and put in the backshell.