Heartbeat Detector (CB25472S)

This heartbeat sensor circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit uses a 741 with a single power supply.

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Controlling a blinking LED with LDR (CB24662E)
The figure shows how to control the blinking of a 5 V blinking LED with an LDR. The LED only...
Band pass amplifier (CB7447E)
Suggested by Maxim in documentation from the 90s, this circuit has its response curve given next to...
Temperature Alarm (CB6111E)
This circuit is from a 1965 General Electric publication. It uses a thermistor to fire a reed...