Timed Alarm (CB6423E)

We found this circuit in a 90's Popular Electronics. The circuit produces a loud sound if S2 is not pressed to reset.

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Two-Tone Humidity Sensor (CB25347E)
We found this circuit in the July 1990 issue of Radio Electronics magazine. The frequencies are...
Stereo Indicator (CB19342E)
This circuit has appeared in several versions in this section and on our website. The transistors can be...
Universal Preamplifier (CB25699E)
We found this universal preamplifier circuit in a March 1994 Electronics Now. It has several types...