About The Circuit
Given below is an IR audio link circuit that has been designed to transmit audio signals as far as 4 meters. The signal is passed on to the base of transistor Q1 through the resistor R4. This signal, when passing the transistor Q1 makes the transmitting diodes D1 and D2 ON.
The circuit has to be neatly designed on a PCB with a 9V PP3 battery for powering the transmitter and reciever. The IR signals that are transmitted are modullated along with the audio input.
The IR signals that are transmitted will be recieved by the photo transistor Q2. On recieving it the emitter voltage of the photo transistor changes according to the strength of the IR signal, which again depends on the sound modullated. Apart from Q2, there are also ordinary transistors Q3 and Q4 which are used to amplify the signal to drive the speaker. Capacitor C1 and Resistor R3 are connected as a filter circuit so as to avoid the interference from all the stray IR signals.
A simple 8 Ohm speaker is enough for the output. The photo transistor Q2 should be an NPN type. They can be anyone like PNZ154, PNA1605F, BPW77NA or BPW85.