7400 competition entry: FM modulation and demodulation system

Alifred and his friend entered a FM modulation, demodulation and transmission system into the Open 7400 Logic Competition.

An input waveform enters the Voltage Controlled Oscillator (VCO), resulting in a FM modulated waveform. This is then sent to an IR LED (through a buffering MOSFET) and is received by a photo-transistor at the other end. The output signal from a photo-transistor resistor network is then fed through a Schmitt trigger to clean the waveform. The signal is then demodulated by using it to trigger a short-pulsed monostable. This results in a charge build up on the end capacitor which is proportional to the trigger frequency, thus recovering the original waveform.

Check out a 1min time-lapse video of their ~8h project development process below.

http://www.youtube.com/watch?v=Np06SkNjhHk

Via the forum.