HX711 AVDD Value for SparkFun Load Cell Amplifier - HX711

Sensors Force & Weight
1

Hi,

I am looking at the schematics https://cdn.sparkfun.com/datasheets/Sen … ll_v11.pdf

And it has the formula AVDD = VBG(R1+R2)/R1

Since R1 value is 20K and R2 is 8.2K. Does that mean AVDD is 1.25*28.2/20= 1.7625V ?

If that is true, then it doesn’t matter if VCC is connected to 5V or 3.3V since AVDD is lower than those possible sources?

If I wanted let’s say 4.5V on AVDD for E+ on the bridge, then I could just change R2 to 52.3K, so 1.25*72.3/20=4.52V.

Please correct me if I am wrong, and if I am correct, what is the purpose of having VCC different from VDD if AVDD is going to be lower anyways?

Thank you very much

:slight_smile:

2

Actually, just noticed both schematics and datasheet published on Sparkfun both have a typo. It should be AVDD = VBG(R1+R2)/R2

So it can make sense to have an AVDD of 1.25*28.2/8.2=4.3V

Please Spakfun correct this to avoid confusion.

The manufacter datasheet can be seen on: http://www.aviaic.com/Download/hx711F_EN.pdf.pdf

I hope this helps someone else who was confused by this typo.

Regards!

3

Hello, and thanks for your post.

I see what you’re talking about.

Looks like the data sheet you linked to is the most current version and is correct, but the notes in our schematic are not, and we have the older version datasheet linked in our product pages and tutorials.

I’ll get this reported to our engineering department to be corrected on the schematic and get the V2 data sheet on our product pages and hookup guides.

Thanks for the catch, you’re the first to let us know!

4

Hola! I’ve retrieved the updated data sheet and corrected the datasheet, schematic, and other links for both the HX711 and OpenScale. I’ll keep hunting through our site to make sure I catch everything, but please let me know if you see the problem anywhere else!

Thank you!