Electrical – HX711 chip not working

energiaload cellmsp430

I'm working on an electronic weight scale using MSP430 and I need your help:

I've written the code using Energia and I've used the HX711 module for testing and everything works just fine. The final project requires everything being on a single PCB, which means I had to give up using the HX711 module (I have to only use the HX711 integrated circuit.) I've remade the schematic that was on the module (see the attachment below.)

hx711 schematic])[1]

I've done some measurements on the circuit and here's what I've discovered:

The Vsup and Dvdd pin are set to 3.3 V as expected.
Base has 2.6 V.
AVDD, VFB and AGND are all equal around 0.7 V.
Also the VBG is 1.8 V.

The schematic is identical to the one attached, but because AVDD and AGND are equal, the voltage that arrives at the load cell is equal to AVDD – AGND which is zero, so I think this might be the issue; I just need a second opinion from you guys (and ways that I can raise that differential voltage.)

Best Answer

I think in your schematic that you haven't tied AGND into proper GND: -

The above is a sample circuit I found on google that clearly shows that AGND connects to a GND symbol and your circuit doesn't appear to. There may be other errors too but this is the most obvious.

Red box and red AGND are my additions to make it clearer to you.

Here's another schematic that confirms this error is quite common: -

Notice the AGND label on the node that goes to the pin named AGND - nodes that are labelled need to be connected.

Picture taken from this forum that also have folk getting confused about the same issue - node names imply connectivity and, it seems, a few folk have just copied the circuit without looking at the data sheet.

And, if you look at the Sunrom schematic directly above where you picture came from you can see all the 0 volt connections inside red boxes (my addition): -

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I had the exact same problem upto an hour ago.

I’m using SparkFun’s load cell combinator circuit diagram here...

https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/SparkFun%20Load%20Sensor%20Combinator%20v11.pdf

...and identified +/-/c on each sensor independently of colour (ca 2kohms between + & -, 1 kohm and dropping with strain between c & +). I had been using screw connectors to make changes easy, especially due to the ambiguity caused by non standard wire colours for each sensor. Obviously at least one connection wasn’t good enough with the screw connectors: It didn’t work after rewiring from scratch several times even with completely different hardware. As soon as i soldered all connections within the Wheatstone bridge and into the load cell amp, it worked fine. After months of frustration, I’ve built 2 scales in the last hour!

Jump leads are fine from the loadcell amp to your arduino/rpi

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