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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
By gorm
#202139
Hi

1)When use 4 loadcells together with the hx711 adc - and adjust the readings so when I have a load on the load cell of 61,9kg the Arduino show 61.9kg. When I take the load of the load cells and add the same load again (61,9kg) I now got new values. I have tried to buy new load cells - but with same result.

1) Another problem is -when I leave load (61,9kg) on the load cells - the values will still decrease - starting with 61,9kg and after 2 minutes fall to maybe 60,5kg and so on.


I have connected 4 load cells (50kg - https://www.sparkfun.com/products/10245 ) to a HX711 - like shown here in the diagram on you site:
https://learn.sparkfun.com/tutorials/lo ... -guide/all

The hx711 is connected to a Arduino Uno - like in the script on the page:
Arduino pin 2 -> HX711 CLK
3 -> DOUT
5V -> VCC
GND -> GND

I need stable values - I am developing a product for sale - I would really appreciate your help.

Thanks in advance

Gorm
By gorm
#202158
Hi there
I found the solution. Until now I connected the load cells black wire to white wire - like on sparkfuns instruction page https://learn.sparkfun.com/tutorials/lo ... -guide/all

But the solution is to connect them like on this page - black to black and white to white... https://electronics.stackexchange.com/q ... 064#196064

So the sparkfun site should notice this.

Gorm
#202160
Not sure why you think the SFE guide indicated to connect black wire to white one. The following seems pretty explicit:
The four wires coming out from the wheatstone bridge on the load cell are usually:
•Excitation+ (E+) or VCC is red
•Excitation- (E-) or ground is black.
•Output+ (O+), Signal+ (S+)+ or Amplifier+ (A+) is white
•O-, S-, or A- is green or blue
Their pictures also seem to indicate four wires with black and white not connected together, and the HX711 board clearly has connections labeled "RED, BLK, WHT, GRN, YLW"
The HX711 Load Cell Amplifier accepts five wires from the load cell. These pins are labeled with colors; RED, BLK, WHT, GRN, and YLW. These colors correspond to the conventional color coding of load cells, where red, black, green and white wires come from the strain gauge on the load cell and yellow is an optional ground wire that is not hooked up to the strain gauge but is there to ground any small outside EMI (electromagnetic interference). Sometimes instead of a yellow wire there is a larger black wire, foil, or loose wires to shield the signal wires to lessen EMI.