Detecting 240volt AC and operating emonTH digital input

(ian) #1


I am using an emonTH to monitor domestic hot water temperature. I now want to add monitoring the Thermostat switch operating. I can separate the cores to and from the thermostat. Is there a non contact way of monitoring the wire from the thermostat such that it can signal a digital input. High when voltage present, low when no voltage present. Ideally battery powered. At worst I could put in a mains relay that is tricky as there appears to be no neutral in the wiring. I am guessing it is very low current.

(Robert Wall) #2

Here’s an idea - but no promises that it’ll work:

If you can get hold of an input on the emonTH processor, then a low value capacitor (i.e. a few turns of insulated wire wrapped around the high current wire on the load side of the 'stat) might pick up enough voltage to show up (digital or analogue) - but you’d need to do something in software to get a steady signal, and determine how big a capacitor (how much wire to wrap around) you needed.

If you’re not counting pulses, that’s an obvious input to try.

(Paul) #3

I’m not sure if it was on here or elsewhere but I’ve come across a neon and an LDR taped together before now.

[Not strictly contactless I know, unless your thermostat already has a neon! but once a neon is fitted there is a level of isolation there.]

(Robert Wall) #4

And it would be OK to earth the other side of the neon - or, if you don’t need to distinguish between 'stat closed and circuit isolated, wire the neon across the 'stat contacts.

(ian) #5

Thanks, I will look at sketch and experiment.