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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Digital control with relays (CB23773E)
With the coded activation of the relays, it is possible to control which of the 16 outputs...
Programmable Current Shield (CB19955E)
The integrated circuit used in this application is not very common. Transistors and resistors...
Mains Voltage Indicator (CB11532E)
This simple circuit makes use of neon lamps to indicate the voltage of a power grid. The lamps are...