Photocardiograph (CB21738E)

We found this circuit in a 1969 Popular Electronics. It measures the heartbeat by changing the transparency of the finger.

Servo Test (CB11388E)
The circuit presented generates pulses at regular intervals with the duration controlled by a...
555 testing generator (CB21341E)
Found in Electronics Now, this circuit generates signals for testing like a signal injector. The...
Neon Flasher (CB20941E)
This simple expandable circuit was obtained from a Popular Electronics from the 80's. The supply...