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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General purpose preamplifier (CB19071E)
This circuit is from a publication from the 60s. The circuit, with minor changes, can be assembled with...
40-Channel Sequential (CB17484E)
We found this circuit in a 1986 documentation. It causes 40 LEDs to flash sequentially. The big...
NCP137 CMOS Voltage Regulator
August 2017 - Mouser Electronics is announcing the availability of the new ON Semiconductor CMOS...