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mharizanov: Detecting AC

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I sometimes have home automation projects that require detecting AC voltage (on/off only), previously have experimented with non-contact AC detection. Here is another approach that may be more suitable for low-power AC detection node: using a NE2 neon lamp and an LDR

 

 

schematicThe bulb will reduce LDR’s resistance and the circuit will read LOW when AC is present and HIGH when it is not (reversed logic). Since the weak pull-up resistor is 150K, this can run on battery operated node in sleep mode with pin change interrupt approach.

Here are some pictures how the sensor came along:

The NE2 neon lamp with 1/4 150K resistorTesting itUsed a piece of pen's tube body to house the partsLDR and NE2 inserted in the tube. NE2's legs protected with shrink tubeHot silicon glue applied to hold them in pieceSome black paint to shield from outside light

Relatively safe and isolated, cheap to build too. Be careful when playing with AC.

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