This circuit is from a 90s documentation. It has a hysteresis and uses a light sensing bridge. The circuit generates a 1000 Hz modulated 10 Hz signal. The signal must be applied to an amplifier.
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...
This positive pulse extender or stretcher was found in a Popular Electronics from the 90s. The...
This circuit was found in Motorola documentation from 1968. SCRs can be modern equivalents and the...