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Last Updated on: Tuesday, June 01, 2021 03:06 PM

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More  Alarm Circuits

designed by David A. Johnson, P.E., 7/8/2000

Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries. However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries. So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time. The device was designed to snap onto the outside of a power cord, where it senses the AC electric field emitted. No direct connection to the internal wires of the power cord is needed. I also included a low battery voltage monitor.

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Unplugged Power Cord Alarm , Circuit designed by David A. Johnson, P.E., 7/8/2000

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