Electronics > Beginners
Load cell question
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german77:
The voltages of hx711 from the ground of the arduino are 8.2mV for A+ and 7.6mV for A-. Not AC voltage that I can measure . The current going through each pin is 8uA. This is not theory any more, those are real measurements.

8uA is what makes the scale to have an offset. To be more realistic if I put my fingers on one of the pins it's enough to give me very wrong measurements two orders of magnitude higher than what the hx711 introduces even when there is 10mA going through that load cell.



--- Quote from: NivagSwerdna on October 11, 2018, 10:02:26 am ---That's a very capable controller.  Might be easier to suck out the measurements over serial.   "11.12 Alibi Tracking" in the manual suggests they are logged.  And then compare with what is declared.
Or just put a CCTV camera over the station.

--- End quote ---
I do use serial to suck out the measurements. Whatever the 720i say I know it's true. I will even don't use the HX711 in this device because I have two serial ports. Not every thing is logged as it's registered manually. Normal CCTV will not suffice since I need to record 6+ months of data in pretty high quality and will not display measurements.

Actually this tread should be closed. The problem is solved by using the second serial port and not needing to use the HX711 anymore. I just still post because it's funny how they think the HX711 is under risk of failure, It has been running 12hours straight without a problem and will last much more. I'm sure it's close to the limits of the op-amp as it's very close to ground. And this is very bad practice, in reality if I connect the serial, the HX711 will fail because the serial port will connect the ground between both devices and now 5v are on my input pins.

Otherwise is a good experiment to try. Next time I will use an instrumental amplifier to attenuate the signals levels to a safe level for the HX711.

wraper:

--- Quote from: german77 on October 11, 2018, 04:03:13 pm ---The voltages of hx711 from the ground of the arduino are 8.2mV for A+ and 7.6mV for A-. Not AC voltage that I can measure . The current going through each pin is 8uA. This is not theory any more, those are real measurements.

8uA is what makes the scale to have an offset. To be more realistic if I put my fingers on one of the pins it's enough to give me very wrong measurements to orders of magnitude higher than what the hx711 introduces even when there is 10mA going through that load cell.

--- End quote ---
I doubt there is no AC at all, but here is a figure to think about: Common mode input AGND+1.2 AVDD-1.3 V. Input voltage shouldn't be below 1.2V against GND.
german77:

--- Quote from: wraper on October 11, 2018, 04:07:24 pm ---I doubt there is no AC at all, but here is a figure to think about: Common mode input AGND+1.2 AVDD-1.3 V. Input voltage shouldn't be below 1.2V against GND.

--- End quote ---

I know, it shouldn't work by what the datasheet says. But the measurements are working not really sure why. I expected to do nothing when I first connected it.
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