Cell loads sometimes giving drifting values

[jmluscher]

Hi I designed a research project using 4 cell loads with 4 HX711 , a ds3231 rtc and a Sd card module.
Hx711 are connected to digital pins 2-9 of arduino Nano and arduino Nano Every(both are susceptible to the problem)

Cell loads are tedea 1042 with a recommended excitation voltage of 12 v. These have 6 wires which I connected to the E, A and B of the hx711

Everything is connected together with a PCB I designed.

I made 2 prototypes and they worked great, then I made 8 more and some of them have one or several cell loads showing drifting tare values, while the rest work perfectly. Around 200 grams going up or down as you turn it on. Then it can drift for 40 grams up and down within a couple minutes.

The problem occurs on certain (always the same) cell load /hx711 circuits so the project is viable but the seems to be an execution or factory defect.

I am experiencing this problem while I power them with my MacBook Air that I use for the calibration of the cell loads. Then I use a 12v supply with a converter to 5v for operation but then I can’t see the values.

I have tried:

• Switching the cell load with drift for the next one with no drift, then the later had the drift. This means that the problem is not in the cell load but on the hx711 or anything before that.

• replacing the hx711 of the drifting scale and this did not solved the problem

• checking and redoing all the soldering of the digital pins and the hx711

I am really out of options. Does anyone have any suggestions that I can try? Is there a way to check if there is something wrong at each step and isolate the problem?

Something that has me wondering is that the hx711 vcc voltage measured is 4.0v while some people report 4.3v. This is for all the hx711 regardless of the drift

Thank you very much in advance for any suggestions

texto en negrita

[xfpd]

Have you graphed temperature at the flex sensor versus drift?

[jmluscher]

I have measured the temperature on different parts of the hx711 to check for overheating
The only temperature sensor I have is in the rtc and the environment is stable, ac at 21 degrees C while doing this.

What do you have in mind? I want to understand

[jmluscher]

After talking to an expert in electronics he suggested that my hx711 modules have a direct of fabrication in many cases so if I want to work with those I will have to do my own QC.

I did and it turned out that 6/13 that I had left were bad!!!

I got them from at least 2 or 3 different sources so they may have different qualities. Just be aware that these modules have a high percentage of defects.

In my original description I said that I changed one module and this was still bad. It turns out that 50% of my spare modules were defective. I only noticed this when I built a QC system where I could test the modules before soldering.

I think this is solved