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Non-contact mains detector

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erifyab

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I'm trying to build a non-contact voltage detector which will trigger a relay if the mains voltage fails in a particular circuit. Has to be non-contact (although could wrap a sense wire around the cable to be monitored). Needs to not be too sensitive (or adjustable) so that only monitors one wire out of several.

I searched on here and found this thread

I built the circuit given in that thread (here). This works after a fashion but only using 2 x 1.5v batts as shown. When I use a 3.3v psu (decent regulated one) it stops working as the output from the 4049 combo only rises to 2.7v in quiescent, so the LED is permanently on and I only get about 1v change in output when it senses mains.

I'm assuming the 4049 is being used as a high gain amp and then oscillator to flash the LED? My circuits theory was a long time ago so I'm struggling!

It'd be really nice to work out a circuit using the 4049 (as I've got loads!) with basically a very high gain amp for the induced signal, with a better sensitivity control and a nice stable 3v output to drive my solid-state relay.

All help gratefully received!

Matt
 
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