The circuit diagram shown in Fig.1 uses a PNA4602M IR detector to receive an IR signal from the remote control. It’s a neat device, which contains an IR receiver, amplifier and demodulator together in a single 3-pin package, and it’s normally used in circuits where you want to decode an IR remote control signal. The way the circuit (Fig.1) works is as follows. When there is no IR coded signal present, the output pin of IC1 remains high. This high signal is fed to the trigger input of the 555 timer (IC2), which being configured as a monostable timer, prevents the timer operating. Whenever you briefly press any key on the old remote control its IR signal is received by IC1 and output pin 1 produces a train of fast moving high and low pulses, which mimic the IR signal code sent by the remote control. We are not interested in this code, but as soon as the signal switches low it triggers the monostable timer IC2 and its output pin 3 goes high for a short period of time, s...