Velman PMLED/5

Discussion in 'General Electronics Chat' started by Wendy, Sep 10, 2014.

  1. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    http://www.vellemanusa.com/downloads/1/pmlcdpmlcdlpmledpmled5gbnlfresd.pdf

    I have got this meter to working on my electronic load, but it is 200mv max scale. I need 2V max. Reading the manual they keep referring to Ra and Rb, but there is nothing like this one the meter, which makes me think they are thinking external resistors. If I have to go that route I'll probably buy a 10MΩ resistor and adjust it that way.

    Figured it wouldn't hurt to ask other opinions first.

    http://forum.allaboutcircuits.com/threads/electronic-loads.38703/
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    They are a bit double in the input impedance.
    In the features they say >100 MOhms and in the specifications they say > 10 MOhms.

    For 2 Volts I would try RB = 9 MOhm and RA = 1 MOhms (when taking the 10 MOhm input impedance in account, RA would be 1.11 MOhms).
    (the scale seems to be adjustable with R2).

    Bertus
     
  3. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    Ra and Rb seem to be external components. I have found the decimal point select. At this point I'm looking to get either a 1MΩ or 10MΩ trimmer post. A 100KΩ would probably work as well too.
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
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    I bought a few of the LCD versions and they came with external resistors. Also, the power supply has to float relative to the input.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Bill, the meter is like the MPJA offerings (http://www.mpja.com/) they are external resistors. When I get back to the farm, I should have a picture somewhere to show how i did it.

    Do you have the chip number available to you?

    John
     
  6. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    The part number is shown on the title. It is the Velman p/n.

    I just have a bit of trouble believing they require external resistors. No big deal I guess.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Bill,

    Here is the board I got from MPJA a few years ago. The two resistors you need to change to adjust the range are circled. They are under the chip. If your board looks similar, I can search further for the datasheet for the display chip that came with the MPJA display. The Velleman link didn't seem to have a picture. The main IC in the meter is an ICL7107CPL.

    panel meter mod PCB circles.JPG

    John
     
    Last edited: Sep 10, 2014
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