AC Voltage monitor

samsn4

I'm wanting to monitor the AC Voltage from a home outlet and eventually input the data into a PC, but first things first. I'm thinking something like AC voltage in to a bridge, then into a comparator that feeds an LED graph . . .


AC

---

> comparator ----> Bar Graph


Thanks for your feedback

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Daniel Mueth

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"Just plug it in and let's see what happens"

Mike Green

You need to isolate the AC line from everything. Given that you want to monitor the voltage, a transformer would be a cheap and very effective solution. The voltage ratio is fixed. A simple 12.6VCT transformer would do very nicely (like this: www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=221292&). You'd want some kind of varistor or other surge suppressor across the primary and you'd want a fuse on the primary.

You could use one side of the winding for sensing and the other side for +5V regulated power for the circuit.

Carl Hayes

Mike's solution is excellent -- but you will save the cost of a few parts if you build only one supply.· Use the unregulated (but rectified and filtered) voltage for measuring, and also to feed the regulator (perhaps an LM7805 -- wups -- you need 3.3v, not 5v, sorry) that powers the equipment.· No need for separately rectified and filtered DC for measuring.

And heed Mike's cautions -- you absolutely must isolate from the line, for safety.· Any transformer except an autotransformer will do that·perfectly.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net

Drone

Hi Daniel,

A couple of suggestions...

Have a look at this circuit:

www.edn.com/article/CA6455602.html

The schematic is attached. Basically this uses an opto-isolator feeding an RC circuit on the output. The result is a pulse-width that is proportional to the AC voltage. Perhaps you can measure the output with a Propeller timer-counter. The circuit is completely isolated from the line.

Fairchild semiconductor has the MID400 AC line monitor chip. It comes in an 8-pin DIP package too.

www.fairchildsemi.com/pf/MI/MID400.html

This part doesn't have an analog output, it is a logic output; but you can set the input threshold where the output is switched.

Enjoy... David