This circuit with different colored indicator LEDs has an expanded scale. We found it in the March 1992 Radio Electronics magazine. For an adjustable range of 0 to 10.5 V.
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...