HX711 Sensor - Weird things happening on external power. [Solved]

I have a HX711 hooked up to 4 half bridge load cells. That is then connected up to a MKR Fox 1200 board which transmits the weight readings over the sigfox network.

When the sigfox board is connected to my pc via USB, I get perfect readings and everything works perfectly. However, when it is disconnected and connected to external it sends through weird/wrong information. The signal is all the place.

I am using the Low Power library which I think may be causing the issue, or is it the changing of the power type. Could it be the battery pack. I'm just using aa 1.5v alkaline batteries

kirwanm1:
I have a HX711 hooked up to 4 half bridge load cells. That is then connected up to a MKR Fox 1200 board

Your picture shows an Uno (5volt logic).
MKR boards use 3.3volt logic, and need special HX711 boards with separate 5volt analogue and 3.3volt digital supplies.
You didn't show how you did power your MKR board.
Should we guess?
Leo..

Yeah, the above diagram isn’t mine. It was just for illustration purposes. Just replace the UNO with the below

Here’s how the MKR Fox is hooked up
with GND → GND, DT->2, SCK->3, VCC->5v

I was under the impression that the HX711 operated on both 3.3v and 5v. Do you have a link or an example of a special HX711 board. I was thought that the 5v in the maker still pushed out 5v even though the mkr operates on 3.3v

So I think I figured it out. On the MKR board itself, I was using the 5v output to run the HX711

If instead, you connect VCC -> VCC (3.3V). All the weird behaviour seems to disappear. I imagine it had something to do with stepping up the signal from 3.3v -> 5V

Going to do some more testing on it to see if I need to recalibrate but everything seems to be working good!

The analogue part of a HX711 board has a 4.3volt regulator, to stabilize excitation voltage for the load cells.
That part won't be stable if you power the HX711 with 3.3volt.

As said, you need a special HX711 board for 3.3volt processors.
You can modify a board by splitting analogue and digital supplies.
Look at the Sparkfun site.
Leo..

The sparkfun is a specific type of HX711 right? Most of the HX711 boards I've come across have a working voltage of 2-5V..

As said before though, if anyone else comes across this thread. Just make sure on the MKR Fox or another 3.3v board to use the VCC output. Using the 5v output causes some weird errors on external power

kirwanm1:
Most of the HX711 boards I've come across have a working voltage of 2-5V..

Wrong.

The HX711 chip has that 2.7-5.5volt working voltage, but not the board.

Sparkfun got that wrong too in their schematic .pdf, but their boards do have the two-supply option.

Just cut the link to the two supply pins of the chip, and power the analogue part from 5volt and the digital part from 3.3volt. How hard can that be (assuming you have some basic soldering skills).
Don't forget to add the decoupling. See the Sparkfun schematic (three caps).

Expect weight instability if you power that board from 3.3volt.
Leo..