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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Limiter Amplifier (CB12468E)
This amplifier for effects on musical instruments can be mounted with BC549 transistors. The...
RF Oscillator LM3909 (CB14292E)
We found this circuit in documentation from National Semiconductor. For the medium wave range the...
Insect Repellent (CB6888E)
According to what is said, the bugs are the female insects (mosquitoes, muriçocas and others)....