Silent alarm (CB22471E)

This circuit is from a Popular Electronics from 1992. The circuit powers an LED when triggered.

Light Controlled Oscillator (CB16728E)
This is yet another version of the light-controlled oscillator that can be found on this website. This...
12 V Regulated Source for Tube Filament (CB20286E)
Originally created to feed the filaments of a 12AX7 as an audio preamplifier to eliminate the...
Presence Monitor (CB12618E)
The incidence of light in the LDR causes this circuit to start operating, emitting a sound whose...