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HX711: VCC and VDD at 3.3V?

Posted: Fri Feb 01, 2019 2:07 pm
by JHH
"PRO TIP: In many cases, you can just short VCC and VDD together. If your microcontroller uses 3.3V logic however, you'll want to connect VCC to 5V and VDD to 3.3V."

What should I expect if I ignore this pro tip and hook VCC and VDD to 3.3V...?

Re: HX711: VCC and VDD at 3.3V?

Posted: Sun Feb 03, 2019 3:59 am
by paulvha
VCC is the main supply, VDD is for the digital interface. The only thing that I expect that would happen is less sensitive readings as the 24 bit ADC is working with 3v3 (AVDD) instead of 5V.

Re: HX711: VCC and VDD at 3.3V?

Posted: Sun Feb 03, 2019 7:08 am
by UhClem
So long as the voltage is greater than the drop out voltage of the HX711 analog supply regulator, it should work fine.

Re: HX711: VCC and VDD at 3.3V?

Posted: Sat Feb 09, 2019 3:50 pm
by JHH
I built a small set-up to answer my own question. Arduino Due, SparkFun's hx711 and load cell in 2x2 conditions:
- with vs without mass on the sensor
- Vcc = 3.3 or Vcc=5.0 V

Meanwhile, Vdd always 3.3V.

Conclusion: when reducing Vcc from 5 to 3.3V, the noise (standard deviation) of the measurement goes up by 43%.
(If you want the details send me a PM...)

Re: HX711: VCC and VDD at 3.3V?

Posted: Sun Feb 10, 2019 1:59 am
by JHH
JHH wrote: Sat Feb 09, 2019 3:50 pm Conclusion: when reducing Vcc from 5 to 3.3V, the noise (standard deviation) of the measurement goes up by 43%.
Ahm... that was a bit to hasty and I cannot find an 'Edit my own posts' functionality...

More specifically, the standard deviation of the masses I measured (in gramms) was:
Vcc=5.0 V : std=2.08 gr
Vcc=3.3V : std = 2.91 gr

This was with the jumper on the bottom sode of the PCB cut, i.e. at about 90 Hz.