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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Remote Control Extender (CB25916E)
This circuit was found in a Radio Electronics issue from May 1989. Please note that it may not...
Photo Thyristor (CB20886E)
The circuit in the figure is very interesting because it simulates an SCR triggered by light. When...
Pulse Generator LM4250 (CB14178E)
The circuit shown is a suggestion by National Semiconductor in its 1994 Linear Applications...