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Davis
01-25-2007, 01:35 AM
Having watched from afar all the neat stuff you guys are doing with stamps, I have finally decided to jump in. My first project will consist of the following:

* Monitor (2) voltage sources (120 VAC) and (3) currents (0-200A via CT's). Periodic samples are OK.
* Monitor (1) CT for current pulses and log the date, time and (optionally) magnitude of each pulse.
* Make this data available for display on a webpage via ethernet

Any recommendations for the appropriate version stamp, literature to get me up to speed, etc. would be greatly appreciated. I was looking at the BASIC Stamp Discovery kit to get started?

TIA,

Davis

stamptrol
01-25-2007, 07:30 AM
Davis,

OK, before heading down this road, your (first) project shouldn't be done unless you have some training in AC circuits. You'll be playing with voltages which can be dangerous to your health. I would have to discourage this as a first project in favor of quite a bit of work at low voltage.

Supposing you're competent at that level, the short answer is that the Stamp will do what you want to do quite nicely.

* to monitor the AC voltage you'll need a couple of PT's to get you down to the 5 to 10 volt level. Rectifiy and lightly filter. Voltage divide if necessary so you get about a max 5 VDC signal to put into your A/D converter.
* same thing with currents, but it may be worth it to buy some transducers which will get you directly to a DC signal. Digi-key has some in your range.
* connect a PINK module to the stamp to make the data available on the web.

Discovery kit and the "What's a Microcontroller" are the classic jumping in points......for good reason.

Cheers,

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Tom Sisk

http://www.siskconsult.com

Davis
01-25-2007, 10:42 AM
Tom,

Thanks for the reply. The AC voltage is the part I DO have experience at, its the ucontroller I'm less than proficient at. Are the PT's necessary or can I go straight to a voltage divider with the 120VAC? I know it would require larger resistors and generate more heat, but that's not a problem in this application. I realize the isolation afforded by the PT's is safer, but this wouldn't be accessible to anyone but qualified personnel.

The PINK module seems pretty expensive at $129 for anything other than hobby applications. I've also looked at the RabbitCore modules and can do the whole thing for $39 including ethernet in quantities of 100. But I'm pretty rusty on C programming and really liked the fact that the Stamp is BASIC programming. Is that the best option for network connectivity?

Thanks again for the help.

Davis

PS - I saw some of your work on the forum, very impressive.

stamptrol
01-25-2007, 09:00 PM
Davis,

Thanks for the kind words.

I'd still discourage using only a voltage divider for measuring high voltage. Two reasons, the first is that you (and your circuitry) won't be isolated from the AC without the PT being there. Secondly, if one of the divider resistors(the one closest to ground) opens, the full line voltage will appear on your measuring circuitry. Regardless, you'll need some rectification to get a suitable voltage for the a/d to work with.

I've used a couple of the other web-server modules out there and still like the PINK best. It essentially works out of the box, and although the instructions were printed with a view to conserving both ink and paper, do cover most issues. As well, there are more and more people on the forum using the unit, so there's a ready source advice/comments.

Regards,

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Tom Sisk

http://www.siskconsult.com

Davis
01-26-2007, 08:47 PM
Are you aware of a source for small PCB mountable PT's? I found a Chinese manufacturer online but they have a minimum of 10,000 pieces, a little out of my ballpark.

stamptrol
01-26-2007, 09:11 PM
Davis,
Probably the cheapest will be to get a couple of small wall-wart power supplies and use them as your PT. If you can find a couple of old modems, the wall-warts for many of the early ones were AC output. But, you need DC anyway, so it may not be worth digging through the yard-sale stuff!
I did a quick search on Digi-Key and they list 1900 PCB transformers. Have a look at 567-1025-5-ND. Less than $5.

Cheers,

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Tom Sisk

http://www.siskconsult.com