HX711 easyC load cell readings are zero (0) no matter what

TECHNICAL SUPPORT Sensors & Modules
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1

Hi Soldered Support Team,
I am experiencing an issue with the HX711 Load Cell Amplifier with Qwiic module while testing a 4-load-cell setup.
The onboard bridge microcontroller (ATtiny404) responds normally over I2C, but all weight/raw readings return strictly 0 (or 0x00 0x00 0x00 0x00).
Here is a breakdown of the diagnostic steps and hardware measurements already performed

  1. I2C Bus & Communication:
  • Hardware address: The board is correctly acknowledged on I2C address 0x30 (Wire.endTransmission() returns 0).
  • Reading behavior: Both using the official Soldered-HX711 library (getRawReading()) and direct 4-byte I2C read requests (Wire.requestFrom(0x30, 4)), the received payload is always 0x00 0x00 0x00 0x00.
  • Timing: Slowing down the polling interval to 1.5–2.0 seconds makes no difference—the output remains flat zero.
  1. Excitation & Power Behavior:
  • Using an analog voltmeter across the E+ and E- terminals, excitation voltage sits at 0 V between readings.
  • During an active I2C polling request, there is a momentary spike to 3.3 V, after which the voltage drops immediately back to 0 V.
  • This indicates that the ATtiny404 attempts to wake the HX711 via PD_SCK, but likely times out waiting for DOUT to go LOW, immediately sending the HX711 back into Power-Down mode and returning empty bytes.
  1. Load Cells & Bridge Integrity:
  • Bridge verification: The four 4-wire strain gauges were verified with a multimeter before connection. The combined parallel resistance values are nominal:
  • E+ to E-: approx 95 Ohms
  • A+ to A-: approx 88 Ohms
  • Leg symmetry (E+ to A+ vs E+ to A-): balanced to within < 0.1 Ohm.
  • Hardware isolation: To completely rule out bridge imbalance or differential saturation, the load cells were disconnected and A+ was directly jumpered to A-. Even with zero differential voltage, readings remain strictly 0, and excitation voltage continues to pulse only during requests.

Questions:

  • Are there any specific register commands or initialization sequences in the ATtiny404 firmware required to keep the HX711 continuously powered up or to read internal diagnostic/status flags?
  • What additional diagnostic steps or test points on the PCB would you recommend to verify whether the HX711 IC or the internal DOUT / PD_SCK traces are operating correctly?
2

Hello @omv_email,
Could you please go to your toolbar in Arduino IDE and go to Tools->Core Debug Level: Debug
and see if there are any i2c errors?
After that, we can try probing the issue further.

3

In did there is a error (see below). I thought IIC is working as I did custom init code earlier where Wire library reported to me that it has found the IIC bus device by its address… but the debug in did reports the error:

HX711 Reading: 0
[ 21444][E][esp32-hal-i2c-ng.c:321] i2cRead(): i2c_master_receive failed: [259] ESP_ERR_INVALID_STATE
[ 21453][E][Wire.cpp:539] requestFrom(): i2cRead returned Error 259

If it helps: I use Soldered’s JST-SH wire (short one) and NULA Mini in the setup.

Also just in case an extra note - that I’ve reverted to the original example easyC sketch for further testing so no code customisation were applied now.

4

I see, unfortunately it seems that you were a recipient of a batch of boards that had its firmware wrongly flashed. The reason why you were able to read the address at 0x30 was that all our boards come flashed with the 0x30 address as default, but the code uploaded to your board was for another device. I am very sorry for the inconvenience. There are two steps which could be taken:

  1. If you are in the possession of a UPDI programmer, you can upload to it the right firmware, which is available here: Soldered-HX711-ADC-For-Weight-Scales-Arduino-Library/extras/attiny_firmware at dev · SolderedElectronics/Soldered-HX711-ADC-For-Weight-Scales-Arduino-Library · GitHub , I can guide you further if you wish to go this path

  2. If you are unable to flash code to the device, you are ofcourse eligable for a refund/replacement, please contact us at the email hello@soldered.com with your order number and a link to this forum topic to start the process