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  • Author Author: sftwrngnr
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Project power measurement

sftwrngnr

I've been thinking about how to measure the power usage of this project, since that is one of the design requirements, and I've decided that what I'm going to do is utilize a separate measurement and logging circuit so that the actual process of measuring the current draw isn't a parasitic draw.  The simplest solution I can come up with is to just have an arduino with a current and voltage measurement circuit attached to it log the data and report it upstream to the website separately.  As I read it, the parameters of the design challenge don't specify that the current draw must be included in the IOT data stream that is explicitly sent up, but do clearly state the requirement for the power measurement to be captured.  The way I see it, provided that I have a mechanism to send the power measurement datastream up to the site, I'm meeting the requirements of the design challenge.  Alternatively, I could have the SI Labs embedded processor pull the data from the Arduino periodically and transmit it to the other device en masse.

 

Any thoughts/Comments/Flogging?

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  • Sounds right to me John.

     

    You might be able to use one of the hall effect current to voltage sensors.

     

    This is a 5A version with 185mV/A output sensitivity. But I think you can get a 30A version that is like 66mV/A.

    https://www.sparkfun.com/products/8882

     

    And there are several 12 bit ADC inputs already available on the EZ32WG controller board expansion header. And the controller board also provides the AEM circuit, that I think can be used in real-time. I know it can analyze energy, V and A, usage and correlate it to your code during debug. You can get all the documentation here.

    https://www.silabs.com/products/wireless/wirelessmcu/Pages/ezr32wg-starter-kits.aspx

  • in reply to RWReynolds

    Hey Rick,

    Thanks for the input! Perhaps I'm overanalyzing it too much, but if I'm using the board itself to measure the power consumption ... by definition, I'm using more power (LOL). I was thinking about this product from adafruit.com: https://www.adafruit.com/products/904, although I'm concerned about the accuracy not being good enough if the device is in a deep sleep.  I got all squishie inside when I read 20 NanoAmps of current draw when the thing is REALLY sleeping.  Granted, its doubtful I'd ever actually get it to that state, but holy crap that's a tiny amount of current draw! I better not be drawing more than a few milliamps most of the time, or I think I have close to an epic failure on my hands. The notable exception would be when the motors or pumps are running, I'm sure they'll get spikey, but for the most part, my hope is that the majority of the time will be spent in a fairly quiescent measure and log mode.

     

    I was definitely planning on using at least one of the ADC inputs for measuring PH/TDS for the nutrient balancing, as well as an external temp sensor for the nutrients themselves so that I can cycle the peltier device to keep the nutrients at an appropriate temperature for the roots.  I live in Arizona/surface of the sun, so that's an actual concern here for me.

  • in reply to sftwrngnr

    I plan on having a separate power bus for the pumps and motors so as to avoid any unnecessary spikes on the device, so I have to measure that independently anyway, but given that the device has a way to measure power consumption on board, I may just eschew my paranoia and go with that for the device power consumption, and include the pump and motor bus draw as a separate data set.... or go totally OCD, measure both externally and use the internal as well. Why not over-engineer?! It's my time and my daughter needs the practice soldering!

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  • in reply to sftwrngnr

    I plan on having a separate power bus for the pumps and motors so as to avoid any unnecessary spikes on the device, so I have to measure that independently anyway, but given that the device has a way to measure power consumption on board, I may just eschew my paranoia and go with that for the device power consumption, and include the pump and motor bus draw as a separate data set.... or go totally OCD, measure both externally and use the internal as well. Why not over-engineer?! It's my time and my daughter needs the practice soldering!

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