Silent alarm (CB22471E)

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

Zener Noise Generator (CB12036E)
The circuit shown is a white noise generator using a zener diode as a source of noise. The...
2-bit decoder 7400 (CB22421E)
This circuit decodes a two-bit value into four outputs (one of four). The circuit must be powered by...
Debouncer 555 (CB11564E)
In the figure we have an anti-ring or debouncer circuit with 555. The duration of the pulse is...