We found this circuit in the September 1971 issue of Radio Electronics magazine. The sensor is an LDR and R1 adjusts the sensitivity. A relay with the appropriate voltage can be used instead of a buzzer.
This circuit is from a publication from the 70s. The operational amplifier is from the period. Modern...
We found this circuit in the October 1992 issue of Radio Electronics magazine. The duty cycle can...
This circuit digitally counts input pulses. The circuit from a November 1970 Radio Electronics uses...