Sensor for heart monitor (CB21075E)

We found this heart rate sensor circuit in a Popular Electronics from the 90s. The placement of the emitter and the receiver is important.

| Clique na imagem para ampliar |

Electronic organ (CB23934E)
We found this simple toy organ circuit in the February 1968 issue of Radio Electronics magazine. The...
Magnetic Transducer Amplifier (CB13102E)
In the figure we have a practical circuit for use with a magnetic transducer. The 20 M ohms...
Linear ramp generator (CB10041E)
This circuit was found in a Motorola documentation from the 70s. The components are from the time,...