Unit is a very sensitive Infrared Receiver Circuit. Most any Infrared
Phototransistor can be used on the front end. The Signal is amplified
by two 3904s and then fed to the amplifier chip through the 10K gain
An 8 Ohm speaker is used to monitor the signal
received. The speaker can be replaced by an 8 Ohm earphone if desired.
It is useful for listing to the audio being transmitted from
clandestine Infrared Voice Transmitters or any other source that is
emitting Infrared signals.