Found in older Signetics documentation, this circuit generates signals from 30 Hz to 25 kHz. Operational amplifiers are from the time, as is the matching pair of transistors.
The circuit shown is based on the LM101A; diodes can be replaced with equivalents. Resistor R1...
With the disappearance of the light falling on the LDR, the relay closes its contacts by...
We find this circuit in an American 1980s documentation. Modern equivalent integrated circuits can be...