Some time ago, there used to be a good web site with serveral great projects, one of wich was a Watt Meter. This site is nowhere to be found nowadays. I will attemp to revive that project.

Please note that I am NOT the original autor of this project. I don't remeber the original author's name (a frenchmen), but he deserves credit for at least the original version, using a MAX4372H High-Side current sense amp to monitor current. The project was built around a PIC16F876A, wich is convinient for this application. It has a couple of 10bit AD, enough pins left to drive the LCD and Flash program memory for fast software tweaking

Another version that I'm currently working on involves using a Hall Effect current sensor from Allegro (ACS750) - that should make the device Brushless compatible!

Fortunately enough I found enough of the original source code left on an old computer to start experimenting. I had to hunt down some missing libraries but it is working now.

I don't have a web site, so I will try to post everything I have on this thread. Keep posted!

Marc

Here's the source code.

It has originally been designed using the free version of CC5X:

http://www.bknd.com/cc5x/index.shtml

The chip originally used is a PIC16F876, I made all my tests using a PIC16F876A, and I suspect that it will work just fine on a PIC16F876B (Not tested)

Marc

Disclaimer: I'm not the author of this software, an I might have modified it a bit from the original version while experimenting. If you are (or know) the original author, please let me know so that I can give proper credits

I actually built it but lost the webpage....
If I have time I'll try to trace out the schematic...

This is a preview of the schematics: (Work in progress...)

I too built it some time ago, but on a breadboard that got used for something else lately.

But it's a great design, so I think it's worth some efforts to bring it back to life

The schematic above came from software reverse-engineering, and some web searching, but it is working - the current sense circuit is missing, since I want to experiment with different methods.

Marc

Great stuff! I was just about to put together an Amp Meter using the MAX4372H, but now have swaped over to using the Allegro part. It seems like a great little device. I'm using a PIC16F877 for development, it seems to be working very well. I was worried that the Allegro sensor was -50 to +50 amps instead of 0 to 50. From the data sheet it looks like 0 amps is 2.5 volts and 50 amps is 4.5volts. That is only 2 volts for the A/D. However the 10bit A/D of the PIC16F877 I'm using gives a 122mAh resolution, the stated max resolution of the Allegro sensor is 250mAh so it looks like 2 volts will be fine. Thanks for the great find Marc! Do you have the sensors in hand yet? I've now got a couple samples headed my way.

-Jim

Hi Jim,

I have requested a few samples of the 50 and 75 amps models, I received an e-mail from them saying the parts would be shipping the next day. This was 5 days ago, but since I'm in Canada that's typical - customs have a hard time dealing with samples

Don't worry I'll let you know as soon as I receive them!

The Pic 16F877 is a very good choice for this application. I just happened to have a 16F876A left from another project that was perfectly suitable for the task (and still in good shape!)

Marc

Please note also that all 3 allegro parts are exactly the same, except for the 50 that has twice the gain of the two others. From the spec sheets, the 100 are fully rated production parts that undergo a different quality control process than the 75.

Of course, if we want a micro power meter, the best option is still the MAX4372H

Marc

This would be the power probe, using the ACS750 ic. The bypass cap is missing. Everything will be encapsulated in epoxy

Marc

It would be great, if a kit or some simple instructions were available, so people with little knowledge of electronics could build one also.

Greetings, Rudolf.

Hi Rudolf,

I will post as much info as I as can when it is available.

I am developping this at a verrry slow rate right now. I will debug the whole thing and create a pcb layout soon. This should simplify things a bit

Let me juggle with the idea of putting a kit together...

Marc

This should be no problem with an AVR. 'course I'll have to write my own code, but I need practice!

Thanks for the links, schematics and most of all, letting me know such a device is possible to build instead of buy!

Allegro samples on the way...

Markz, What A/D are you planning on using for the voltage sensor? I'm considering the ICL7109 right now but am open to suggestions.

-Jim

I've been using the ACS750 for about 12 months now in the electric power steering power amp I built at work for our development vehicle. It's a good sensor, but for our use it needs to be calibrated and linearised (then store the values in a lookup table for the micro to read) if you want to achieve better than the 1% or so accuracy they claim, otherwise you may as well just use a 7 bit A/D. I incorporated on into a BLDC controller with a pic16F84 ages ago when I was playing with the early Kokam cells to modify the rx's signal to the esc to keep curent under control to stop the cells from dying at a massive 3C - oh how things have changed! It's one of those things that could easily be added permanently inline with an esc with a small connector coming out to plug into a volt meter so that you can check current in the model without the hassle (and extra losses & voltage spike causing induction) of plugging a Wattmeter in.

Stu.

Markz, about your schematic in post #4. If IC1 is an LM317 (or similar) regulator, shouldn't R1 be connected between the OUT and ADJ pins instead of OUT and GND?