Silent Alarm (CB6444E)

This circuit simply triggers an LED when the sensor is activated. The circuit is from a Popular Electronics of the 90s.

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Two-tone solar buzzer (CB20493E)
This circuit was found in a 1991 publication. The transistor can be a general-purpose type....
Optical PFM Receiver (CB15961E)
In the figure we have a receiver for frequency modulated light signals (see the transmitter in...
Pulse Width Multiplier (CB6349E)
This circuit is intended to increase the width of a pulse. The circuit is TTL and can be used as a...