Load cell meter design

Discussion in 'The Projects Forum' started by frpr666, Dec 28, 2014.

  1. frpr666

    Thread Starter Active Member

    Feb 2, 2010
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    Last edited: Dec 30, 2014
  2. frpr666

    Thread Starter Active Member

    Feb 2, 2010
    37
    6
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You could replace R3 with a 200 ohm variable resistor (multi-turn potentiomter) plus a 910 ohm fixed resistor to balance your bridge.
     
  4. frpr666

    Thread Starter Active Member

    Feb 2, 2010
    37
    6
    Hello,
    I tried to build it. I used R9,and R10 instead of the real load cell, R1 is 1k
    I didn't have MCP6002 on my hand, instead, I used MCP602 as IC1 (it doesn't have R2R input).
    Then I checked the output with an 12bit. ADC@Vref=3.3V/ uart converter.
    It seems that the outputs measured values have picked up a noise...
     
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You might want to try adding a capacitor across your LM385 reference. Also, add external resistors as needed to bump your reference to 1/2 of supply voltage instead of 1.2 v.

    If that is not enough, add another resistor between neg supply rail and your inAmp ref input.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Šťastný nový rok!

    Why R20?
    Why is IC1A needed?
    Why is IC1B needed?
    Where is the anti-alias filtering?
     
  7. frpr666

    Thread Starter Active Member

    Feb 2, 2010
    37
    6
    Thank you for replies very much!
    I thought IC1B would make calculation (y=1.5*x-0.5*vref) to 'extend' the IA output range {0.7V..2.3V}. But now it seems it is not so important.
    I will remove IC1A, IC1B and I try again...
    There is also similiar application note in TI DS INA126.

    Edit1: the results are much better with the anti-aliasing filter. Even when tested on DIY board...
     
    Last edited: Jan 3, 2015
  8. frpr666

    Thread Starter Active Member

    Feb 2, 2010
    37
    6
    Hallo,
    please I would have one more question regarding the balancing input bridge.
     
  9. frpr666

    Thread Starter Active Member

    Feb 2, 2010
    37
    6
    Hallo analog experts,
    I had a chance to make an update. Please what you think about the schematic?
    I would like to know your opinion. I didn't design such complicated thing so far.
    The result seems good. 'Green' is the value as a number after ADC conversion (0..3V)->(0..4095).
    'Red' is LM385 reference. The MCU makes simple calculation n=(n1+n2+..+n8)/8.
    The 'm1' pictures are for IC1A:Vout=~2.5V.
    The 'm2' pictures are for IC1A:Vout=~0.6V.
     
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