“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…?
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.
So long as the voltage is greater than the drop out voltage of the HX711 analog supply regulator, it should work fine.
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…)
JHH:
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.