New Propeller based open source energy meter
Jay Kickliter
Posts: 446
My friend just got back from Memphis showing off our student project at the APPA conference there. Since it's out in the open, I figured I'd officially post it here. In a different thread I asked for name suggestions, and am leaning towards MegaJoule, but Frank and I havent had time to discuss a name, so for now it's nameless.
What is it? An energy meter. Meant as wireless equivalent off the Kill A Watt, or for a house's primary energy meter. Read more about it at my website. As I mention on my site, this project is going to be on hold for about four months. My design partner is getting commissioned as a nuclear officer in the Navy, and I have to go to sea for a few months. If anyone wants to work on it while I'm gone, go ahead. I'll give you contributor acces to our google code page.
The funny things is that this started off as just a senior EE side project for us. We designed and built it in one month and didn't expect as good of results as we're getting. At the conference, Frank said several utilities were actually interested in it. Particularly since it can be built so cheap, and they don't have to pay royalties for the design. That might sound like a bad deal for us, but the original contract we had to sign for scholarship had us signing away intellectual property rights for the project. We figured if we can't make money off it, might as well make it open source, so we modified the contract.
If all you want is details, here they are:
* Propeller based of course
* Mesh networkable
* Uses a current transformer for current measurements
* True RMS, so accurate even with non-pure sine waves
* Accounts for power factor using Heater's FFT (his code should help us calculate THD also)
* In it's current configuration, can accurately read currents to about 12 A, with about 10 mA precision
* Open source, so you can make and sell them if you want
Just be careful, it is beta, and some obvious safety precautions are still missing, like on-board fuses for both neutral and hot mains wires. That one bit me in the rear. I hooked up the leads backwards. You're thinking, it's AC, why does that matter? It matters when you hook the ground clip of an oscilloscope probe to the board's ground, which is connected to AC hot, and you blow an entire PCB trace.
So have at it. Just remember you're working with mains voltage.
What is it? An energy meter. Meant as wireless equivalent off the Kill A Watt, or for a house's primary energy meter. Read more about it at my website. As I mention on my site, this project is going to be on hold for about four months. My design partner is getting commissioned as a nuclear officer in the Navy, and I have to go to sea for a few months. If anyone wants to work on it while I'm gone, go ahead. I'll give you contributor acces to our google code page.
The funny things is that this started off as just a senior EE side project for us. We designed and built it in one month and didn't expect as good of results as we're getting. At the conference, Frank said several utilities were actually interested in it. Particularly since it can be built so cheap, and they don't have to pay royalties for the design. That might sound like a bad deal for us, but the original contract we had to sign for scholarship had us signing away intellectual property rights for the project. We figured if we can't make money off it, might as well make it open source, so we modified the contract.
If all you want is details, here they are:
* Propeller based of course
* Mesh networkable
* Uses a current transformer for current measurements
* True RMS, so accurate even with non-pure sine waves
* Accounts for power factor using Heater's FFT (his code should help us calculate THD also)
* In it's current configuration, can accurately read currents to about 12 A, with about 10 mA precision
* Open source, so you can make and sell them if you want
Just be careful, it is beta, and some obvious safety precautions are still missing, like on-board fuses for both neutral and hot mains wires. That one bit me in the rear. I hooked up the leads backwards. You're thinking, it's AC, why does that matter? It matters when you hook the ground clip of an oscilloscope probe to the board's ground, which is connected to AC hot, and you blow an entire PCB trace.
So have at it. Just remember you're working with mains voltage.
Comments
Another very cool project. Thanks for sharing both to the forum, so we can see what you're up to, and for making it open source so that others can use it and learn from it. Best of luck to you and your buddy while deployed. Be safe. And thank you both for your service.
Regards,
Peter
If I find any time to do a write up for this project, I'll post it here. But otherwise this project is going straight to abandon-ware until next Fall. If anyone does want to build one, I'll be around for another month and will clarify any questions.
As for a parts list, I'm attaching a BOM file from DigiKey. It doesn't have part names, sorry. If I can figure out how to use Eagle's BOM function I'll post a proper parts list with part names.
So that's what it was! Here I was thinking, of course they're running their 'scope from an isolation transformer (or battery powered ScopeMeter".)
PE -- I had a supervisor insisting that I run the scope across a live ac circuit much as you describe. I stood my ground (!!), refusing, and it went **kapow** when he landed that probe. Everyone but everyone turned around, but I was in the clear. "I'll go get that unneeded isolation transformer - for the others, [name withheld]." In my tool box I still have the TO-3 FET that he blew a hole in the top of.
-Phil
Well done, that's a neat project and nicely documented as well. I'm a proud to have been able to donate a little software to the cause. I might try to find time to try and put the THD calculations in there.
Now you've done it. "Her in doors" has no understanding or appreciation of my electronics and programming tinkering at home. But when I showed her your project she immediately perked up a suggested I build one. She has a thing about "green issues" and is always on about all the energy my computers and gadgets are wasting:)
-Phil