Voltage/Current measurement

braineater · Post by **braineater** » Wed Apr 14, 2004 4:49 pm

I have posted the same thing at the lcdc forums....

I'd like to use my mx222 to monitor the voltage/current of the ac mains .

Basically , I'd like to build some inline sensors so I can monitor the power consumption of each circuit at LAN parties (tripping breakers sucks )....

I'm curious if anyone has any ideas on the best way to accomplish this.

However I build these sensors , they need to be reasonably accurate , and they MUST provide isolation from the mains.

After some more research,I have discovered that dallas semiconductor has devices that may work.
At this point I'm curious about exactly what support the mx222 has for one wire devices.
will it only support the one wire temp sensor ? or is it capable of interfacing with any one wire device ?

Miles · Post by **Miles** » Wed Apr 14, 2004 5:02 pm

The MX Series is capable of interfacing with any one wire device assuming the protocol guidelines are followed. Please see the following link for the MX2 manual. The 1-Wire Command is explained in great detail in section 6, page 29.

http://www.matrixorbital.com/manuals/LK ... USB_02.pdf

braineater · Post by **braineater** » Wed Apr 14, 2004 7:13 pm

aha
The old RTFM eh ? haha

Thanx....that was exactly what I was looking for.

/me slaps self

Miles · Post by **Miles** » Fri Apr 16, 2004 10:17 am

You can also see the following tutorial for additional information: http://www.lcdforums.com/forums/viewtopic.php?t=1736

braineater · Post by **braineater** » Fri Apr 16, 2004 1:11 pm

Thanx miles.

At this point , it's a hardware issue.......
Apparently , Dallas semi/maxim does not have such a device/application.(this kinda surprizes me , you'd think it was a common industrial use).
In an effort to build one using stuff they do have....
I found these :
crmagnetics
With one of the AC lines thru the hole , it will provide 0-10vac proportional to a 0-20 A current.
At this point , I'm not sure whether it's better/easier to directly sample the ac with an a/d converter......or use a bridge to convert to dc and sample that.....
We'll see what dallas semi thinks ...

Paradigm · Post by **Paradigm** » Tue Apr 27, 2004 12:28 pm

Thought I should chime in here. You're asking a for a tall order. Power/Voltage/Current measurement at 120VAC is NOT cheap. Looking across www.digikey.com, you could get something like:

http://www.digikey.com/scripts/DkSearch ... t=32375306

For $84 usd, (there are higher current models). It takes upto 20A produces a voltage that varies with how much current is passing through the loop. This is the easiest since you don't have to splice the power cable to take the measurement. But very costly.

Next up would be something like:

http://www.digikey.com/scripts/DkSearch ... 36&Site=US

which you have to splice into the line. It can take 20A and "only" costs $38 usd. One disclaimer I must make is to BE CAREFUL with 120VAC. It's enough to do damage or even start a fire. There are circuit precautions that should be taken. Everything from PCB layout to components that protect it from surges, spikes, and other bad things MUST be concidered. By far not as simple as the first item.

Either way, you're then going to have to get that analog signal into the digital realm. With a little analog circuitry (2 resistors) you could scale that voltage down and feed it into a DS2450 1-Wire Quad A/D Converter.

The last piece would be software. From what I know LCDC only supports temperature probes. This might change, but I'm not the person to talk to about that

braineater · Post by **braineater** » Mon May 17, 2004 9:47 am

heh....shoulda checked back here sooner.

Thanks for the input Paradigm.

Although I hav'nt done much on this recently (my casemod project is eatin up all my time and money

) , I was definitely thinking along the lines you suggested ,namely the DS2450.....

While the split core xformers and whatnots are nice , As you said they are $$.....
I've setup a 15 A Variac test circuit...I'll wind my own cores , so providing the ~5v input the DS2450 needs won't be an issue.

Hehe...I hafta say , yer disclaimer made me giggle..No worries sir.I'm an Electrician and an avid electronics/physics hobbiest (120 VAC pfffft)...So If I light myself up , It'll be my own damn fault.

braineater · Post by **braineater** » Mon May 17, 2004 9:47 am

oooop....double post.