Door buzzer or alarm (CB20492E)

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

Rectangular Generator With Active Cycle (CB10492E)
This circuit is from a 1998 Electronics Now and can be easily assembled since it uses a common...
Incandescent Lamps VU Meter (CB17345E)
This circuit triggers three incandescent light bulbs following the audio signal applied to its...
DC multiplier LM339 (CB15190E)
This circuit was obtained in the SGS manual of linear integrated circuits of 1982. The components used...