HX711 and Arduino Pro Mini @1mhz


for my beekeeping project I want to measure the hive weight with load cell and HX711.

The Arduino Pro Mini that I use runs @1Mhz so I can go down to 1.8V and use sleep function. The build will run from 2x AA batteries.

The problem is that the HX711 reports wrong values.

I made two different tests: Same power supply, same HX711 chip and load cell. Tho different Arduino Pro Minis.

  • The one working @8Mhz by default, measures correct values.
  • The other, @1Mhz with burned fuses, measures wrong values.

I am guessing there is no problem with the HX711 or power running around 3V. The HX711 datasheet states that the chip can run down to 2.6V.

So I tend to believe that the problem occurs when I burn the fuses of the Pro Mini to run @1Mhz.

Can anyone confirm that this is the problem and/or propose any solution or workaround?

best regards, George

Common HX711 breakout boards use a 4.3volt power supply for the load cell (excitation voltage). That 4.3volt supply needs at least 4.5volt to work. Leo..

I am not sure this it the problem.

I even tried this modification that modifies the HX711 for 3.3V. I used a 10K resistor and the excitation voltage is now 2.2V.

I tried once again, to be sure, using 3.3V, default Arduino Pro Mini 8Mhz, and HX711 and I get correct readings. When I use the mod on the Arduino Pro Mini @1Mhz with all the rest being the same, the reading are totally wrong.

mirmigki: I used a 10K resistor and the excitation voltage is now 2.2V.

The "GDN+1.2" and "VCC-1.3" limitation calls for an absolute minimum excitation voltage of 2.5volt. Datasheet mentions a minimum VDD of 2.7volt. The 3.1volt (12k), of the article, sound ok. Why not run the Arduino and modded HX711 from a single LiPo cell. Why not sleep the whole setup for extended periods, instead of running it at a lower clock speed. Leo..

The plan is to post data to the gateway every 30 minutes.

The code puts the Pro Mini into sleep, and only checks every 8s (for now) if a magnetic reed is triggered. The reed is used to check if someone opened the hive.

And every 30 minutes it posts the weight, battery voltage, temperature and humidity.

The original plan was to use the Pro Mini @1Mhz so it can run down to 1.8V. I also removed the Leds and the regulator.

But I then found out that the HX711 cannot run that low. Maybe I have to use the default operation of the Pro Mini running @8Mhz with the drop-out voltage of 2.7V which is the same as min voltage of the HX711.

I will just have to replace the batteries sooner.