Hi Meca,
The 42 digit DVM is most likely a misprint.
Check the values posted in the d/s Table.

If you do not have a 9.999mV DVM, try this method.
1. Program the HX711 for a Gain of 128.
2. Connect each L/C in turn [ one at a time] and, using the Arduino IDE Serial monitor, Note the Raw data Count.
This will give you a value equivalent to the L/C value of the Table
Identify the Lowest Count L/C and divide the Count by the 128 Gain value [ you should know the L/C stated mV/V from the L/C calibration sheet].
3. Using the values from each of the 4 L/C's you can then determine how to adjust the 100R Vext trimpot for each L/C.

I would use this method.
Buy a INA say a AD623, set the gain for 1000, use a regular DVM to measure the AD623 Vout and follow the procedure in the Table. In effect, extending the sensitivity of a 1V FSD DVM to 0.001V

Note: As the AD623 is a single supply you will need to add a +Vref, so that Vout, for Vin=0v is about 0.1V.
E

If none of the above are acceptable, use the moving the weights around each corner as described in the d/s

 

Hi E
I am reading page #2 and this recommend used high sensitive voltimeter a least 42 digits for pre trimming the potentiometers. I don't have multimeter with high sensitivity. Do you have any alternative for make calibration process with commercial multimeter?

I believe that is some sort of formatting error and should read “4-1/2 digits”. So any good meter that can read out to 3 places or so.

 

Hi Meca,
The 42 digit DVM is most likely a misprint.
Check the values posted in the d/s Table.

If you do not have a 9.999mV DVM, try this method.
1. Program the HX711 for a Gain of 128.
2. Connect each L/C in turn [ one at a time] and, using the Arduino IDE Serial monitor, Note the Raw data Count.
This will give you a value equivalent to the L/C value of the Table
Identify the Lowest Count L/C and divide the Count by the 128 Gain value [ you should know the L/C stated mV/V from the L/C calibration sheet].
3. Using the values from each of the 4 L/C's you can then determine how to adjust the 100R Vext trimpot for each L/C.

I would use this method.
Buy a INA say a AD623, set the gain for 1000, use a regular DVM to measure the AD623 Vout and follow the procedure in the Table. In effect, extending the sensitivity of a 1V FSD DVM to 0.001V

Note: As the AD623 is a single supply you will need to add a +Vref, so that Vout, for Vin=0v is about 0.1V.
E

If none of the above are acceptable, use the moving the weights around each corner as described in the d/s

Ok E. I will follow your proposal and I will buy AD623 but have a doubt. What do you mean FSD?

 

hi Meca.
FSD, Full Scale Deflection, the Vsignal maximum at the rated maximum load weight of the L/C.

eg: say an L/C was rated at 1mv/Vext of excitation and the value of Vext =10V and the L/C maximum weight load was10kG
Then a 10kG weight, with a 10Vext would output 10mV [FSD].

BTW:
I have run test HX771 sketches using this method and it gives acceptable results.

If you do not have a 9.999mV DVM, try this method.
1. Program the HX711 for a Gain of 128.
2. Connect each L/C in turn [ one at a time] and, using the Arduino IDE Serial monitor, Note the Raw data Count.
This will give you a value equivalent to the L/C value of the Table
Identify the Lowest Count L/C and divide the Count by the 128 Gain value [ you should know the L/C stated mV/V from the L/C calibration sheet].
3. Using the values from each of the 4 L/C's you can then determine how to adjust the 100R Vext trimpot for each L/C.

If You need a test sketch, I could post a copy.
E