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assistance needed: Wireless Energy Meter

Former Member

Hi everyone,

One group of our students in STEAM Club is working with Climate Cycle (climatecycle.org), and we have a bicycle (from last year) that generates electricity. We were interested in measuring and tracking the power output, and setting the bike (and two others that we're assembling) outside the lunchroom for students to recharge their cell phones during lunch periods. We could monitor power generated short- and long-term, and have a monitor displaying that information next to the bikes.

 

I found a project through Hackaday.com that attaches an Arduino pro mini to a power meter and then uses an antenna to send the power info to another Arduino. Here is the project URL: Gizmosnack: Power Plug Energy Meter - Now wireless!  (and here's the preceding post, where he figures out how to sniff the data from the power meter: Gizmosnack: Power Plug Energy Meter Hack). We have the Arduino Pro Mini, the NRF24L01, and the same energy meter that he uses, and we'd like to emulate his project using the code he has provided. To that extent, no problem. The obstacle that we've run into is getting the connections correct between the Arduino, the antenna, and the power meter. I left a quick note on his blog, but am not sure if we'll hear back with the specific info we need, and after examining the pictures closely, we're not entirely confident in our analysis of the connections. The next obstacle I anticipate is correctly hooking the power meter up to the bike, since we're using it in a different setting. But hopefully that won't be too hard to figure out, since the bike already has a Watt's Up wired in. And then we may encounter difficulties with the code, but that's in the future. I loaded the first sketch into the Arduino IDE and was able to find and load the requisite libraries, so that it verified properly, but once we start actually using it I'm sure we'll need assistance.

 

My own technical knowledge is limited, just from two years of messing around occasionally, using projects other people have put together, as in this instance, and then modifying them. So what assistance do we need? For now, can anyone lend any insight, based on the pictures on his blog, into the specific connections we need to make between the Arduino, the nRF, and the power meter? Any advice or suggestions would be appreciated. And then as the project moves forward I'm sure we'll have more questions. thanks, Keith

  • 0

    Update: Kalle Lofgren, the author of the blog post, updated his post with a wire diagram a little while ago, so that's one problem solved, and I guess I cried wolf on this one. We're trying to get at least a prototype ready for this Saturday, so we're rushing a bit. I'll let you know if we have more questions as we move forward. thanks, Keith

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    sounds like it was pretty easy to identify the SPI bus in the meter. The author does warn you not to take the 0V as earth as it must certainly will be neutral and you should not connect it to your earthed PC or any other earthed equipment they could mutually kill each other. Use digital isolators to make the connection to the meter and the arduino or Rasp Pi or whatever.

  • 0 in reply to peterjcs23

    Thanks for the pointer. In this case, what are our concerns if we'll be using the power meter exclusively on the bike (never plugged in to the wall), and not connected to anything external (bike generates power, power meter measures power, info read by Arduino, transmitted wirelessly by nRF)? Can I simply follow the wiring diagram he's added to his post and be in good shape? Any thoughts on how the meter would be used to read power generated by the bike? I'm wondering if I need to wire it directly into the system like the Watt's Up is wired in currently (see attached schematic that comes from Climate Cycle, who guided our initial assembly of the bike), or whether I can actually use it in its plug/outlet form.

     

    And you can assume, without worrying that you're insulting me, that I'm pretty ignorant as far as electrical connections and wiring. I know how to use a soldering iron and the Internet, and that keeps me one step ahead of the students, learning as I go, but not a very big step. thanks, Keith

     

    Climate Cycle energy generating bike schematic (note Watt's Up power meter at top):

    image

  • 0 in reply to Former Member

    ...so, if your scheme is not earthed you should be okay. As you have no mains neutral connection you could connect your system 0V to earth for safety. If you plug in a USB port, a software emulator (JTAG) or use an earthed instrument like an oscilloscope then they are earthed and will connect your system to earth through these instruments.  It is just something to keep in mind if you get odd results (or a puff of smoke).

     

    The plug in meter will measure current flowing into the neutral pin, I would guess. It may not measure voltage, cheap meters often assume the voltage is 240 or 110 and assume a frequency of 50Hz or 60Hz. So your measured current will probably flow from the front connection (Load) to the mains pin (Source) on the neutral. Power in watts is I x V but as I say V may be assumed. If it is assumed your bike will have a variable voltage and the results will be misleading. If your meter does measure voltage it will be measured between the line connection on the front and the neutral connection.

     

    Hope that helps, the above is all a guess,  it is bit suck it and see when you're breaking into an unknown meter.

  • 0 in reply to peterjcs23

    Thanks for the info. We started soldering yesterday,so we'll be able to start messing around with it soon, and then we'll see what we see. I'm glad you mentioned the possibility of the cheap meter voltage assumption, it will help to know what might be happening if we're getting unusual numbers. Should have more to report next week. thanks, Keith