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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Optical communication transmitter (CB7849E)
This circuit was found in a 90s American documentation. The circuit uses an LED that can be of a...
Damped Oscillator (NI012E)
Damped sine oscillations can be produced when short pulses are applied to the input of this...
50 W amplifier TDA1514A (CB15371E)
We found this circuit in the Philips integrated circuits manual of 1990. The circuit must be...