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I.R Headphone System (Transmitter)


The 555 forms on oscillator generating pulses at a frequency of about 100kHz. Pin 5 on the 555 is the "control voltage" pin. A voltage applied to this pin will vary the frequency of the oscillations. If the input is an audio frequency alternating voltage, it will modulate the frequency of the oscillator. We therefore have a frequency modulated (f.m.) infra-red beam.



The value of R depends on the number of transmitter diodes used; for two diodes, as shown in the diagram, try R = 82W. If a higher transmitted power is needed, try the arrangement shown below:



The vero for the transmitter can be almost the same as the vero for the transmitter for the "I.R. switch".


I.R Headphone System (Receiver)


Transistor: 2N3819 (f.e.t.) Integrated circuits: 4046 phase-locked loop used as an f.m. demodulator; 4069UB hex inverter.


Vero diagram

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