Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

Capacitor Test (CB4825E)
In this circuit the capacitor under test is charged at switch position A and then discharged...
Stereo FM Transmitter (CB18734E)
This is a common circuit in the 1990s, when experimental FM transmitters were in vogue. The...
Body Heat Detector (CB25684E)
Using a piezoelectric sensor of the time, this circuit was found in the February 1994 issue of...