THE RECEIVER
The Receiver is also made of a 555 timer IC used as a detector. Also using a PNP transistor (part number BC558) as switching for the 555.
The signal is detected via a phototransistor which is ANDed (using LM7408) to reduce fluctuations and ripples coming from the signal source. This circuit is derived from a missing pulse detector, we modified it to work as a pulse detector for our receiver.
Source : http://www.falstad.com/circuit/e-555missing.html