HX711 with 4 equal resistors in a wheatstone bridge config

Something fishy going on.
According to the datasheet, E- must be tied to ground, and E+ comes from a PNP transistor that is being regulated down by the HX711 to ~4.25volt (if you work out the feedback resistor divider ratio).

Like to see clear pictures of both sides of these boards.
Leo..

I just realised I had extras, and were able to measure a 4.25V on E+ on a new one (DT and SCK were floating). I dont know what happens if I try to ground them, I could check

Don't ground an output pin (DT)!

pics

E+

E-

front

back

traces with backlight
Annotation 2020-07-08 084159.jpg

This appears to be one of those boards in which E- is not grounded (as mentioned by @Smajdalf). And, there's no ground plane (for noise reduction)...

I also have a Sparkfun HX711 but haven't soldered pins to it. Its E- is tied directly to the ground plane.

This probably ought to be split off as a separate topic, since it now appears to be unrelated to the OP.

Annotation 2020-07-08 084159.jpg

Thank you for the images.

E- is normally grounded through the board.
The green board doesn't have E- connected to ground through the board.
If you don't, then the E+ regulator also isn't working, because it's 8k2 feedback resistor (8210) is floating.

It seems that with these boards you also must connect E- to Arduino ground.
Leo..

Wawa:
If you don't, then the E+ regulator also isn't working, because it's 8k2 feedback resistor (8210) is floating.

It seems that with these boards you also must connect E- to Arduino ground.

With E- grounded, E+ is 4.39v

This appears to be another example of "you get what you pay for" and caveat emptor.

The 8k2:20k resistor ratio on this module, with the 1.25volt reference of the HX711, works out to
(8200 + 20000) / 8200 * 1.25volt = ~4.3volt

0.09volt off is ok for a 5volt Arduino, but 4.39 volt is a bit close for a Nano on USB power (~4.6volt supply).

You must of course know what you're doing if you order undocumented cheap parts.
Leo..

Hi,

I have what seems the same board and looks same, seems wrong as per everything I have read on the net.

I have also other boards with different layout that I am willing to analyse per DaveEvans study of Noise Free resolution test. Here my post: https://forum.arduino.cc/index.php?topic=365107.msg4676152#msg4676152

Thanks for all your work.

My best regards,

Wawa:
Thank you for the images.

E- is normally grounded through the board.
The green board doesn’t have E- connected to ground through the board.
If you don’t, then the E+ regulator also isn’t working, because it’s 8k2 feedback resistor (8210) is floating.

It seems that with these boards you also must connect E- to Arduino ground.
Leo…