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.

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Moving scale DC voltmeter (CB7341E)
This circuit was found in an American publication in 1966. The circuit uses a general-purpose FET that...
Simple Alarm (CB19221E)
This circuit has no lock, but it has a very low consumption feature in the standby condition. We...
FM Local Oscillator (CB4293E)
This is the typical circuit of a local oscillator for a superheterodyne FM receiver. The circuit...