This VCA was found in the July 1988 issue of Radio Electronics magazine. It uses an OTA op amp and has its gain adjusted by the voltage at the gain input.
Found in a 90s Popular Electronics, this touch switch uses a single sensor. PLLs are common today....
We found this circuit in an old documentation from 1979. It is a logic level tester that is...
This ultrasonic insect repellent was found in American documentation from the 1980s. The...