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I am currently using strain gauge based load cells and want to weigh 1-5kg granular products on whatever container with 4loadcells beneath. I encountered a problem with connecting load cells in a parallel position. I thought it would work, but nothing showed up as I expected. A single load cell works well with a hx711, the amplifier, but when I link four load cells, parallel doesn't work. The loadcell I use and a circuit are in the picture shown above.

What type of circuit junction box make all the loadcells in parallel contain? And how do I manage that?

Please tell me how to handle that issue most efficiently?

enter image description here I don't know what type of hx711 module it is, bought it from some Chinese importer, but it looks like exactly what you see in the picture

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    \$\begingroup\$ had you connected two of them backwards? Choose one load cell as the reference, then check the polarity of each other cell to that. Then try again with them all in the same phase. \$\endgroup\$
    – Neil_UK
    Apr 18, 2022 at 12:29
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    \$\begingroup\$ If they were a set, intended to be connected like that, then that would be the right thing to do. If they were a set intended to be connected to a specific PCB from some scales, then it might not be. Testing them in pairs to check phasing also checks whether any of them are shorted, thus stopping your whole quad from working. Look at it this way. You've tried something, it didn't work, you've asked the question. I've asked you to do something that you haven't done yet. Worth a try maybe? \$\endgroup\$
    – Neil_UK
    Apr 18, 2022 at 13:42
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    \$\begingroup\$ Do you have a DVM? 'Got nothing' means nothing, you always get something. You're putting 5 V on the red wire and 0 V on the black wire? With each load cell connected individually, measure the voltage on the green and white wires with zero deflection and full load deflection. Do the same for two cells in parallel. What are you using to power the cells? It's possible that two or more in parallel are bringing your supply down. 'Reading data through the arduino serial' for debugging is like trying to eat spaghetti with chopsticks, wearing boxing gloves. Get down and dirty with the volts and wires. \$\endgroup\$
    – Neil_UK
    Apr 18, 2022 at 14:16
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    \$\begingroup\$ Is your 5 V source capable of driving several load cells in parallel? Where is the datasheet of the load cells? What is the maximum current of the 5 V source? What is the resistance of each bridge resistor of the load cells? \$\endgroup\$
    – Uwe
    Apr 18, 2022 at 14:16
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    \$\begingroup\$ Here is a datasheet ardu.dk/wp-content/uploads/2015/03/Vejecelle-YZC-1B.pdf The excitation voltage should be 10 to 15 V. Input Resistance may be as low as 400 Ohm. You probably need a amplifier to a decent voltage for the arduino, 20 mV may be too small for the ADC input. But I would not trust a datasheeet with MV/V instead of mV/V. They should know the difference between megavolt MV and millivolt mV. \$\endgroup\$
    – Uwe
    Apr 18, 2022 at 14:53

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This should work: the source resistances of the load cells are usually very close, and the Thevenin equivalent of this circuit is a voltage summer (averager).

There is a catch: while this may be OK at DC, it usually underperforms at AC, since the parasitics of each cell affect all the others. You’ll end up degrading AC CMRR versus using a dedicated in-amp or sigma-delta ADC on each cell individually.

Since you’re using a two-channel sigma-delta ADC connected directly to the strain gages, your best bet is to use two of them. You connect two load cells to each HX711, and can multiplex between them. This will still be way cheaper than using four instrumentation amplifiers and a single ADC. You can also buy other 4-channel ADCs that can take such low-level inputs: either multiplexing them, or sampling all four in parallel.

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  • \$\begingroup\$ This should work only if there is enough current to feed 4 load cells in parallel instead of only one. The HX711 seems to be designed for one load cell only. \$\endgroup\$
    – Uwe
    Apr 18, 2022 at 17:19
  • \$\begingroup\$ @Uwe Would you recommend some other amplifier that can manage? \$\endgroup\$
    – Tumenbayar Munkhjargal
    Apr 18, 2022 at 17:46
  • \$\begingroup\$ like common in the market \$\endgroup\$
    – Tumenbayar Munkhjargal
    Apr 18, 2022 at 17:47
  • \$\begingroup\$ I could not recommend any other amplifier. I would look for an amplifier with explicit specification of parallel load cells or an amplifier that may be used with a separate feed. \$\endgroup\$
    – Uwe
    Apr 18, 2022 at 18:26
  • \$\begingroup\$ @Uwe HX711's power supply regulation is optional and uses an external pass transistor. You can excite the load cells from a separate regulator if you wish, but that's not usually necessary. Just select a pass transistor that has a good gain at the strain gage excitation current desired, and HX711 will control it just fine. In any case, the OP didn't even intend to supply the gages using HX711's built-in regulator it looks like. \$\endgroup\$
    – Kuba hasn't forgotten Monica
    Apr 18, 2022 at 21:52

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