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I'm pretty new to the world of electronics and was working on an Arduino project using load cells and HX711 amplifiers. The project consists of four HX711 connected to the Arduino and Pi, with all sensors sharing the same ground and power.

I have by now gotten everything working, but I did notice something I thought was strange. When running code to only use a single HX711, that sensor worked fine. But when code was run to use all four HX711, that same sensor would not work. The cause I found out was there was what seemed to be too much resistance from the ground connection on that HX711. Doing some resoldering fixed the issue.

So I was wondering what causes this. Why does the ground connection work when it is the only HX711 working, but not when there are more running? It was my impression that if the connection is good enough when running one sensor, it would be enough for it when running them all.

Here's kind of what the circuits look like (minus the CLK and DT connections to the Arduino): Fritzing example of my wiring

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    \$\begingroup\$ A (proper) schematic would be better, but for something this simple what you have should be ok. \$\endgroup\$
    – Tyler
    Nov 5, 2019 at 19:54

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The problem is in the resistance of the cable, which causes the ground voltage of the part to fluctuate an not be at or near 0V. Sine most circuits need their ground to be at 0V.

It could have interfered with digital communication if the wire size was small enough

Since each HX711 uses 1.4mA of current resistance in the ohms range of the ground could produce voltage offsets in the ground in the mV range which could be bad for the analog electronics as well.

Most of the time a ground should be less than 1Ω in a setup like this, a great ground should be in the 10mΩ's or less.

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  • \$\begingroup\$ When the ground line from one sensor hooks into the ground line from another sensor, the current flow through the cable will also create a voltage drop along the ground cable, given that the cable is not ideal and exhibits some resistance. This will shift the ground level of the sensor which can affect analog measurements. The best solution is the "star network", where each sensor has its own cable directly to the battery. \$\endgroup\$ Nov 5, 2019 at 20:54

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