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 |

Differential Amplifier (CB6546E)
This circuit was found in an American publication from 1968. The transistors are from the time,...
Tone Control Preamplifier (CB18561E)
This preamp with several inputs using germanium transistors from the time was found in Japanese...
Crossing Signal for Railroad Modeling (CB3854E)
This circuit uses two sensors that are placed at the intersection of a miniature railway, causing...