Photocardiograph (CB21738E)

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

Battery Monitor TLV379 (CB20385E)
This battery monitor circuit with the TLV379 low voltage operational amplifier was obtained in the...
Red Alert (CB12179E)
We got this circuit from Radio Electronics from July 1990. The circuit mimics the sound of the red...
100 kHz Crystal Oscillator (CB4853E)
This configuration often addressed on this site is from a 2000 documentation. The circuit can be...