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  • Author Author: jw0752
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Cheap Chinese Volt Amp Panel Meter won't zero

jw0752

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A while back I bought 8 of these small 0 to 30 Volt 0 to 10 Amp panel meters from China. I like to use them in my builds because they have in the past worked well for my needs and they are very inexpensive. The other day when I needed one for a new project I found the 4 of the 8 would not zero on the Amp Scale. They would say 2, 3, or 4 in the least significant position and this number would add to the actual current that the meter was attempting to read. This put the meter outside the small trimmers range to calibrate. Further the trimmer had no affect on the meter's 0 level display. I can accept some inaccuracy from these inexpensive meters but I knew I could not tolerate a meter that had a reading when it should have read zero.

 

I mention this problem in case anyone else has purchased these meters too. Here is what the board side looks like:

 

imageimage

 

I have devised a patch fix to the board that clears the problem and allows the regular I ADJ trimmer to do its job.

 

I will be glad to share the patch but only if someone has some of these with the same problem. Let me know if you have had a similar problem and I will continue the blog.

 

John

  • Hi

    My voltmeter turns on but only shows zero
    I reset but it didn't work

  • Glad   found the data sheet.Big thankful to y'all. But I found a guy testing his way trough the paths and thought I'd share it.

     

     

    I found it rather delightful to watch...

    Clem

  • in reply to ralphjy

    Hi Ralph,

     

    Not sure but most likely they came from Banggood or through EBay. Let me know if you do anything further with them. Reprogramming would be well above my skill level.

     

    John

  • in reply to jw0752

    Great!  I'm glad that it worked.  I just wish something like that was better documented.  I have a crazy notion of trying to see how that MCU is programmed or maybe just reprogramming it for fun.  I read that the update rate on the meter is somewhat slow.  I'll need to get around to ordering some meters but have lots of other projects to do.  Did you get them from Ali Express?

  • in reply to ralphjy

    Thanks Again Ralph,

     

    The reset worked on all my meters. I took my hardware patch off and reset the meters and solved the problem. Now I will have to get busy and find a new application for the 100K trimmers and 1 Meg resistors  image. I also appreciate the schematic that you found as I am never happy with things the way they are and may need to modify one of these meters in the future. The schematic makes this a possibility.

     

    John