💬 Micro (nano) ampere meter (double)




  • Contest Winner

    I like it! Great work! :)
    I realized this idea nearly year ago, but I am so lazy... so I didn't post it )
    This is my variant:
    0_1493204825884_IMG_2017-04-26_110025.jpg
    I can make some suggestions.
    We can add a switch which will short inputs sometimes for automatic calibration. I used sealed contact relay.
    It is not clear for me how you realize input offset (input signal of HX711 should be between AGND+1.2 and AVDD-1.3 according HX711 datasheet. So I do it in the following way which is not optimal but easy:
    0_1493206665757_measure1.png


  • Hero Member

    Parts ordered from a local shop, I should be able to make the assembly next week :)


  • Hero Member

    @Koresh The offset is accomplished with a 2 * 1k voltage divider between Aref and gnd.
    It is probably a good idea to list all our (undocumented) projects to share with the MySensors community ;)


  • Hero Member

    Hello @AWI,

    I made one, but I have a problem with the refresh rate.
    As I have no jumper at the back to set refresh rate like on HX711 breakout board, I lifted the pin 15 (RATE) on my breakout board to connect to VCC using a 10k resistor.
    So now it's sampling at 80Hz, but the refresh rate is still a bit slow and the reactivity of the button is really bad. Despite setting only 2s to switch to next channel I have to keep the button pressed for several seconds more for the screen to change. And I need something like 2s press to trigger the offset setting.
    Do you have the same behavior or do I have to fix some settings in the code (didn't look into the details at the moment...) ?

    Thank you for sharing this great little project !

    0_1494046539514_IMAG1674.jpg


  • Hero Member

    @Nca78 Looks good, Hard to say why the response is slow. There is quite some averaging in taking readings from the ADC and I tried to find a right balance between accuracy and response time/ button behaviour. For me it is not spot on but very usable.
    You could try to remove some of the averaging to get a better refresh rate. (i.e. the "32" to "8")


  • Hero Member

    Wow, those HX711 modules really are inexpensive. As little as 48 cents each on Aliexpress.
    http://www.aliexpress.com/store/product/HX711-Module-Weighing-Sensor-Dedicated-AD-Module-For-Arduino-Free-Shipping-50PCS-LOT/716258_32228651474.html?spm=2114.12010615.0.0.MWbQV9
    I just ordered some from Amazon for about triple that price, but, meh, they'll be here this Sunday, not a month or two from now, so I'm cool with that. I'd like to use them to measure the rate of charge on some solar nodes that I'm in the process of figuring out how to make. Not sure, but at a mere 48 cents each, I might even bake them into the final design instead of being forced into a much longer measurement interval that the 10 bits of ADC on the ATmega328P would require.

    So, thanks for this great project write-up! It tipped me off to go look into it. And while I'm at it, I may as well make this project too. :)

    [Oops. I cancelled my Amazon order, as I just noticed that I should have ordered the shielded version, which Amazon doesn't appear to have. ]


  • Hero Member

    @AWI said in 💬 Micro (nano) ampere meter (double):

    @Nca78 Looks good, Hard to say why the response is slow. There is quite some averaging in taking readings from the ADC and I tried to find a right balance between accuracy and response time/ button behaviour. For me it is not spot on but very usable.
    You could try to remove some of the averaging to get a better refresh rate. (i.e. the "32" to "8")

    Missed your answer when you posted it. Thank you for the suggestion, I will try to reduce the number of samples and hopefully I will find a good balance between reactivity and precision.
    Else I will use 2 touch buttons in toggle mode so it will never miss a command.


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