We found this circuit in an old publication. The components used are rare today. Accuracy depends on the resistors in the input selection network. The circuit operates from 10 to 500 kHz.
Found in a Popular Electronics from the 90's, this circuit detects the approach of objects by the...
This old 4-channel circuit was found in the December 1994 Electronics Now magazine. The circuit uses...
The figure shows how to implement an alarm buzzer in an LM3914 to warn about crossing the scale...