residential voltage sensors to pic components

Hi, Tyler. One way to do this is to loop the residential power wire through a current transformer, and terminate the output of the transformer with a resistor. That will give you an isolated AC voltage proportional to the current used at the outlet.

You can rectify that signal and use it directly, or use it as the input to a comparator, which would give you the logic signal.

Note: DO NOT use a current transformer without terminating it with a resistor! Hazardous voltages can result!

Good luck Chris

Hi Chris Could you explain what you mean by "loop the residential power wire through a current transformer" ? I'm curious about the physics of your "Note:". What is happening with and without the resistor? Sorry for the dumb questions, but I'm an elderly electronics virgin :)

Hi Chris,

thanks for the reply. I had wondered about ammeter type components. Given that it is passive it is probably what best fits my needs.

I did a quick search for current transformers and as you might expect found quite a few. In any case I will do some experimenting with some smaller power sources (providing I can find a cheap CT that will work with low voltages first) before I go playing with the more dangerous stuff.

Thanks

Tyler

Chris wrote:

See this brief description of current transformers:

You basically have a toroid transformer which one wire of the AC line is passed through. That wire then becomes the primary winding of the transformer and a voltage proportional to that current is produced in the secondary winding. Some current transformers have built-in electronics so that their output is a DC voltage or a varying current in a 20ma loop configuration. These units are not cheap. See this list for some "sale" prices

Determining whether a device has power available can be done with a solid state relay (SSR) with logic level output such as this one for

24 to 120 volts or this one for 220/240 volts also has others for 12 volt DC to logic level, etc

John

You want cheap? How about $3 or $4 USD?

Depending on the current you want to switch at, I'd try the PE-51688 to start with. Put your 240VAC wire through the donut hole (if you're not getting enough signal, loop it once), and rectify the signal, then use a comparator to determine when current exceeds your preset.

One small current transformer, diodes, and 1/2 of an LM393 with a voltage divider for your reference, and you're pretty much there.

Not so bad.

By the way, please bottom post if you have future questions. Read Google Groups Help Topic "What's good 'netiquette' when posting to Usenet?"

Cheers Chris

a current transformer or hall-effect sensor followed by suitable amplification.

It won't detect the plug but if the device it drawing power it will detect that.

Bye. Jasen