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Saturday, July 11, 2009

Simple IR Audio Transmitter Circuit

This is a simple design for infra red audio link that can be used as transmit audio signals up to 4 m. The circuit is based on 3 transistor and one photo transistor. The photo transistor Q2 can be any NPN photo transistor like PNZ154, PNA1605F, BPW77NA or BPW85. And the transistor is using BC548. This is the figure of the complete circuit of the simple IR Audio Transmitter circuit.

Operation of the circuit the signal to be transmitted is applied to the base of Q1 via resistor R4. The transistor Q1 drives the IR transmitting diodes D1 and D2. The audio input will be modulated to the IR signals transmitted. The transmitted IR signals will be picked by the photo transistor Q2. The emitter voltage of the transistor Q2 will change according to the sound modulated to the IR signal. The transistor Q3 and Q4 amplifies this signal to drive the speaker or headphone. C1 and R3 form a filter to avoid interference from stray IR signals. For power supply, this circuit is use 9V PP3 batteries for powering the transmitter and receiver. An 8 Ohm speaker or a headphone can be used to hear the sound.


  1. NPN photo transistor is three pins transistor.. But you showing only 2 pins connection and 1pin where to connect.?
    Plz Reply...

  2. Photo transistor only has 2 pins. The "third" pin is internal: it's activated by the infrared light emitted by IR diodes D1 and D2.

    This circuit works, though it is sensitive to light unless you use an IR filter over Q2, and you will get a buzz over the audio output. A schmitt trigger could be useful in "squelching" that...

  3. what is D1 and D2? is it both of that are infrared transmitter or D1 is infrared transmitter and the D2 is infrared receiver? please reply asap..tq.