Modification of the IR sensors

Modification of the IR proximity sensor was suggested by a youtube video. The problem the mod solves is illustrated by DIY & Digital Railroad .

There are two objectives of this modification:

  • Move the IR transmitter (clear) and IR Photo Transistor (dark) to the back side of the circuit board.
  • Reduce the size of the LEDs from 5mm to 3mm so they fit between the ties.

By moving the two parts to the back, the small circuit board can be mounted flush with the underside of the layout with the Tx and Rx extending up through base board with only two small holes between the HO railroad ties. For example these several numbered blue board. This keeps the adjustment available.

While carefully removing the original parts be sure to note the location of the cathode, flat spot on the base of the LEDs. Both cathodes are in the middle of the board. When installing the replacement LEDs be sure both cathodes, flat spot, short leads are in the middle.

I used a short peace of shrink tubing to prevent shorting of the leads as they are pressed up through the base board.