Found in American documentation from the 1980s, this circuit makes use of components of the time, which are uncommon today. The circuit detects the approach using a sensor formed by metal plates.
Found in the CQ radio amateur magazine, this circuit generates a standard 100 kHz signal. The...
Although it is a common configuration today, this circuit was taken from an old publication. The...
This digital instrument input circuit was found in the September 1989 issue of Radio Electronics...