This circuit is from a 1977 Radio Shack manual. The photocell is an LDR and the operational one is a 741. Components with non-standard values can be approximated.
We found this circuit in a 1973 documentation. The null adjustment trimpot is 10k. The circuit can be...
This circuit is from Radio Electronics from April 1977. The circuit is for analog lines using...
The indicator for this circuit is a mini buzzer with a 1.5 V oscillator. The circuit can also be...