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Questions &/or issues related to products in the Flex / Force category should be posted in this forum. includes Force Sensitive Resistors, Load Cells & Amplifiers, Pressure Sensors, etc
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By MorganJ

I am a working on utilizing your OpenScale for a 24/7 digital scale for monitoring a display shelf on accurately send data regarding the weight of its contents over time.

My current setup includes the following:
1 - SparkFun OpenScale (SEN-13261) Firmware v1.2
4 - 50Kg Load Sensors (SEN-10245)

Please see attached pictures for configurations.

After following the guide at ... okup-guide.
I was able to tare and calibrate the scale with accuracy (including creep calibration 30+ min, tare, 30+ min calibration).

However, upon adding and removing weights from the scale I am noticing that the registered weight on the scale becomes more inaccurate. Also if an item is dropped onto the scale, and levels out, the weight that is displayed is not correct and can be off by over 200% of the actual weight. Even further, when removing all items from the scale the output value will not be at or close to zero. And continues to be off by larger values over time.

My question is:
What could be causing these miscalculations?
Is this because the Load Sensors are not designed for this application? Should we be using other sensors?
Is there a problem with the hardware setup? Do I need to invest in another board on top of the current setup? Is there a problem with the platform?
Is this a known issue, vibrations causing misreadings, etc.?
Or is there another method that we can follow to increase consistency?

I look forward to hearing from everyone and their opinions!
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User avatar
By TS-Chris
Hello, and thanks for posting your question in the forums!

I see a few things that could be causing you trouble.

  1. It looks like you're using a breadboard to connect the load sensors to your OpenScale
  2. There isn't a hole in your platform to allow the load sensors to flex.
Load sensors output a tiny voltage and any stray resistance introduced by a breadboard will have a large impact on the reading you get for them. The only real way to solve this is to solder every joint. You do also need to clean the flux residue off the board when you are finished soldering because flux is slightly conductive and will cause your readings to drift as well.

For the sensors, you need a cutout in your platform that allows the sensor to bend or flex when you apply a weight otherwise you won't get an accurate reading. The image below shows the area that needs to be free to move.
Here's a picture of a platform we made here with four load sensors:
And here are closeups of the top and bottom of one of the sensors:
If you make those modifications, that should help a lot.
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