Photocardiograph (CB21738E)

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

Debounce Circuit with the 555 (CB1472E )
This circuit was found in a telecommunications publication of 1978. Its purpose is to obtain...
4 input mixer (CB6309E)
This setting appears with variations at various points on this site. This is from a Motorola...
Commercial MW Radio (CB18313E)
This circuit is from a 1967 documentation. The circuit uses germanium transistors and has an...