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Helllo,
I am using load cells in my research project. I have 4 load cells and have connected 4 HX711 modules (one to each load cell) and have connected them to the arduino uno.

I have taken the example code given for 2 load cells and modified it for 4 load cells. My complete code is available here. The original HX711 2 load cell library example code is available here.

I have referred the source code but still have the following questions:
Q1) The following part of the code:

boolean _tare = false; //set this to false if you don't want tare to be performed in the next step
byte loadcell_1_rdy = 0;
byte loadcell_2_rdy = 0;
byte loadcell_3_rdy = 0;
byte loadcell_4_rdy = 0;
while ((loadcell_1_rdy + loadcell_2_rdy + loadcell_3_rdy + loadcell_4_rdy) < 4) { //run startup, stabilization and tare, both modules simultaniously
    if (!loadcell_1_rdy) loadcell_1_rdy = LoadCell_1.startMultiple(stabilizingtime, _tare);
    if (!loadcell_2_rdy) loadcell_2_rdy = LoadCell_2.startMultiple(stabilizingtime, _tare);
    if (!loadcell_3_rdy) loadcell_3_rdy = LoadCell_3.startMultiple(stabilizingtime, _tare);
    if (!loadcell_4_rdy) loadcell_4_rdy = LoadCell_4.startMultiple(stabilizingtime, _tare);
  }

Is this written correctly? Can this be removed or is this part necessary?

Q2) I wish to increase the sampling rate so I am going to increase the baud rate to 115200 or higher. Does this have any affect on the previous question? Since, the source code seems to have been written for 10SPS.

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  • You don't need 4 ADCs to measure 4 load cells, you need to configure the 4 load cells as Wheatstone bridge and measures it with one HX711 ADC. SparkFun has a good introduction on Getting Started with load cell which explain the details.
    – hcheung
    Jul 20, 2022 at 4:33
  • Also the higher the sample rate, the noisier the data it become. For a weight scale, accuracy is more important than speed, what is the point of increasing sampling rate. BTW, HX711 sampling rate requires hardware configuration changes. Read Olkal's HX711 library README for more information and why 10SPS is chosen.
    – hcheung
    Jul 20, 2022 at 4:52
  • @hcheung I am not talking about 4 strain gauges in a wheatstone on a single load cell. I need to measure 4 different forces hence I am using 4 different load cells.
    – Atharva
    Jul 20, 2022 at 5:11

1 Answer 1

-1

It is better to use a chip from Analog Device AD7799. It has relatively high accuracy and no swimming, compared to the HX711. When connecting 2 load cells of 50 kg on the pavement the scheme has an accuracy of 10 grams. I use the AD779x library.h and an example program that appears in the file-examples menu in arduino, after installing the library. When hx-711 is connected to the same the accuracy of my sensors was 30 grams, I measured the accuracy of both ADCs for 10 minutes. I ordered AD7799 on Ali for 2-3$ . You need to take it together with the adapter for the ssop16 c chip the distance between the terminals of the adapter is 0.65 mm. You also need to take "solder paste with solder", because the conclusions are too small and close. I took the SMD capacitors from the damaged matplate, measuring them capacity by tester. When the load cell is warmed up with a hairdryer, the data changes greatly. Perhaps you need to put a digital ds18b20 thermal sensor on the thermal sensor on the thermal watch. With even a short - term when you touch the load cell with your finger, the readings also change greatly due to the sensor warming up from body heat. If you touch through several layers of folded paper, the sensor does not warm up and the readings do not change. Those who will test load cells by pressing them with their finger should remember that in a few seconds, after touching the load cell with their finger, the heat will reach the sensor's sensing element along its metal body and the values will float up or down by tens of grams, depending on the connection scheme, sensor type, duration touching. Press the sensors with any objects, not with your hand directly. L The inductance may or may not be set. It is possible to connect without a reference voltage source TL431, and directly from the arduino 5v with a filter of 2 capacitors (as shown in the diagram). I first connected without it and the readings were quite normal. We need to try... The power source used from Hi-link.enter image description here

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