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I'm trying to flash an LED when an AC current is over 4 amps. To do this, I'm using a current sense resistor of 0.01 ohms. That gives a threshold of 40mV. But I can't figure out how to use this voltage to trigger the DC LED flashing circuit. I thought of an optoisolator, but 40mV isn't enough to run it. Any other ideas on how I can "connect" the AC to the DC LED circuit?

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    \$\begingroup\$ Is there a separate power source for running the LED and any associated circuitry? Or are you trying to power the LED with the 40mV AC? \$\endgroup\$ – DarenW Jan 24 '13 at 6:08
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If you can get some power off the AC side, you can make some DC and use a comparator to sense the 40mV and have it light an LED. The LED would be the one in the optoisolator, and you can go across to the isolated side and have that trigger your flasher circuit.

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