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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Continuity Test (CB11841E)
This continuity test is very simple to assemble and has great sensitivity detecting the presence of...
Manual Bistable (CB25670E)
This circuit was found in the January 1994 Electronics Now magazine. The transistors are general...
Remote Control Receiver (CB25900E)
Based on Radio Shack 276-137, this circuit was found in the December 1995 issue of Electronics Now magazine....