Photocardiograph (CB21738E)

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

800 Hz Sinusoidal Oscillator (CB13572E)
This circuit is from an old publication from 1977 and can be implemented with more modern...
Gain 100 buffer (CB9558E)
This basic buffer circuit can be implemented with other operational amplifiers. The circuit is...
5V x 3A Regulator (CB5468E)
This circuit can be applied to other 3-terminal regulators and equivalent transistors can be used....