Photocardiograph (CB21738E)

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

Light change detector (CB22058E)
This circuit only detects variations in light falling on the sensor. The circuit uses an LM380 as a...
Locking circuit with the LM3909 (CB14294E)
This latched switch configuration was obtained from National Semiconductor documentation on the...
Wheel of Fortune (CB20962E)
This electronic roulette circuit with 10 numbers was found in a Popular Electronics from the 80s....