Found in a 90’s Electronics Now, this circuit has its output connected to an audio amplifier. The transducer is the type that fits on the finger to monitor the transparency and thus the beats.
This temperature compensated circuit was found in a Popular Electronics of the 1990s. The circuit...
This circuit generates sequence of pulses in order and times determined by the capacitors in pins...
This 1970s RCA circuit can be triggered by light or dark, depending on how the LDR is connected....