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 |

Touch or leak alarm (CB22092E)
This circuit was found in old documentation. The SCR can be any of the 106 family. Note the sensor...
Staircase generator (CB21847E)
This circuit was found in Ferranti's 1974 transistor manual. The transistors are from the period and...
Transistor relaxation oscillator (CB12680E)
Short duration pulses can be obtained with the relaxation oscillator that uses common transistors and is...