Hello Friends, I made the software for a truck scale per axle, but I have a question, before carrying it out I wanted to see if they think it is feasible that Arduino can handle the 8 cells of 2000kg/4500lbs each (It would be 2 bases with 4 cells each one, load cell shear beam) the cells are 3V and 4 wires and 350 ohm. Can they be connected to the hx711?
chelo46:
...the cells are 3V...can they be connected to the hx711?
Not sure if this means the cells are self-powered or are rated for a max input voltage of 3v.
If the latter (rated for 3v input): they may work with the HX711's 4.3v, but the cells will need to dissipate two times as much heat (proportional to V squared) and carry 43% more current. Self-heating may cause errors. But, if you only read them momentarily and infrequently, maybe it wouldn't be a problem.
If the former (self-powered): the HX711 is intended to be used with load cells driven by the HX711's excitation voltage (about 4.3v). I doubt you would get reliable results if it is used with self-powered load cells, since small variations in the self-power voltage may cause large errors. And, if you can modify the cells to accept HX711 power, then you need also to check the maximum differential voltage output when excited with 4.3v. If you know the max diff with 3v, then multiply that by 4.3 / 3 ... the result must be 16.8mV or less for use with the HX711 Channel A at normal gain of 128, or twice that with 64 gain.
But, if all that is ok, then consider using this library: GitHub - compugician/HX711-multi: An Arduino library to interface multiple HX711 units simultaneously
DaveEvans:
Not sure if this means the cells are self-powered or are rated for a max input voltage of 3v.If the latter (rated for 3v input): they may work with the HX711's 4.3v, but the cells will need to dissipate two times as much heat (proportional to V squared) and carry 43% more current. Self-heating may cause errors. But, if you only read them momentarily and infrequently, maybe it wouldn't be a problem.
If the former (self-powered): the HX711 is intended to be used with load cells driven by the HX711's excitation voltage (about 4.3v). I doubt you would get reliable results if it is used with self-powered load cells, since small variations in the self-power voltage may cause large errors. And, if you can modify the cells to accept HX711 power, then you need also to check the maximum differential voltage output when excited with 4.3v. If you know the max diff with 3v, then multiply that by 4.3 / 3 ... the result must be 16.8mV or less for use with the HX711 Channel A at normal gain of 128, or twice that with 64 gain.
But, if all that is ok, then consider using this library: GitHub - compugician/HX711-multi: An Arduino library to interface multiple HX711 units simultaneously
This is the data sheet of the load cell, the maximum allowable voltage of 15V and an unspecified minimum, I contact the manufacturer and according to them there is no specific minimum, that is, the output will be variable and proportional according to the source of that is used, that is, with 4.3V the hx711 should have an output current of 12.9mA, is it correct? In other words, there would be no problems making them work with the hx711, right?
Allowed exitation voltage 5-18V
recommended exitation voltage 9-12V
Another way of feeding the load cell would be through a summing box and a transducer that is fed with a range of 6-38VDC. Connect 4 load cells to a summing box, connect another 4 cells to another summing box and then i send those two signals to the transducer.
This transducer has an output of 4-20mA, 0-20mA and 0-5V, as I said, it is fed with a voltage ranging from 6-38VDC. and connect those 0-5V to the arduino.
Ok, so the 3v was a red herring.
Sounds like they should work with the HX711.
But the max output differential voltage (under your full load, with 4.3v excite) is still unknown. Judging from the allowable excitation voltages, it probably isn't a problem, but I would want to know it, if I were you.
I have no idea about your adding box and transducer.
DaveEvans:
Ok, so the 3v was a red herring.Sounds like they should work with the HX711.
But the max output differential voltage (under your full load, with 4.3v excite) is still unknown. Judging from the allowable excitation voltages, it probably isn't a problem, but I would want to know it, if I were you.
I have no idea about your adding box and transducer.
Hi Dave, no no, the adding box and the transducer would only be useful if the hx711 was omitted, that would be an alternative connection without the hx711.
My intention is to know if you think it works only with the hx711. Here I attach the complete data sheet.
See the "rated output" of 3 mv/v at the top of the list? That means when the load cell is under the rated load, the differential output will be 3mV per excitation volt. So under rated load with 4.3v, the output will be about 13 mV. So you're ok with the HX711 Channel A at 128 gain.