HX711 Overflow Issues

Projects General Guidance
1

Hi guys, I've been trying to figure out what is wrong with my circuit. I'm using a HX711 connected to a balanced wheat bridge setup. I continuously get an overflow value no matter what I do. Any guidance to a newbie like me?

Thanks in advance!

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#include "HX711.h"

// HX711 Pins
const int LOADCELL_DOUT_PIN = 2;
const int LOADCELL_SCK_PIN = 3;

HX711 scale;

void setup() {
  Serial.begin(9600);
  Serial.println("HX711 Raw Output Test");
  
  scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
  
  // Set gain (try 128, 64, or 32 if getting OVF)
  scale.set_gain(128);  // Start with 64 to avoid overflow
  
  // Optional: Tare the scale (reset to zero)
  scale.tare();
}

void loop() {
  // Read raw 24-bit ADC value
  long raw_value = scale.read();
  
  // Print raw output
  Serial.print("Raw HX711 output: ");
  Serial.println(raw_value);
  
  delay(500);  // Adjust delay as needed
}
2

You need to post schematics.

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3

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sorry about that, and sorry its a little scuffed

4

I see you have only powered half of the HX711.
Both VDD (digital part) and VCC (analogue part) of the HX711 need power.
For a 5volt -logic Arduino, connect both to 5volt.
For a 3.3volt Arduino, connect VDD to 3.3volt and VCC to 5volt.

The resistors must be perfectly matched to get the bridge balanced.
Measure between A+ and A- with a DMM for less than 20mV.
Leo..

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5

Because of float read();

6

How exactly did you balance the bridge?
I see no trimpots?

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7

The board in that schematic does not match the board shown on the breadboard.

Can you measure the resistors of the and identify the voltages as per #4? The resistors should all match closer than 0.020V/5V=0.004=0.4% to keep the A+/A- difference less than 20mV and keep the HX711 from overflowing.

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8

Good morning! Measuring it gives me a range of values from 0mv to over 200mv.

9

I'm using some resistors that I got off of digikey that are 350 ohms with 0.5%. My strain gauge is roughly at 351ish. I can see that my setup is really imprecise. What kind of trimpot should I get?

10

Channel A can be programmed with a gain of 128 or 64,
corresponding to a full-scale differential input voltage of ±20mV or ±40mV respectively, when a 5V supply is connected to AVDD analog power supply pin.

You need to reduce that voltage far down from 200mV in order to not have HX711 overflow issues.

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11

What strain gauge?
I only see 4 resistors.

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12

Its the strain gauge I plan on using to replace one of the resistors, my apologies for the confusion.

13

The strain gauge manufacturers often recommend using identical strain gauges as resistors for precision and temperature compensation.

14

Using trimpots and one strain gauge in a bridge on a solderless breadboard is OK for experimentating but not practical for a real world application.

What are you trying to build?

15

I'm trying to create a device that needs to detect when a radial load is applied to a hollow cylindrical rod. This rod is mechanically fixed on one end, which also has the strain gauge in the inner part. I am a mechanical engineer so this is really out there on my comfort zone. The closest thing to something like this I've built is a battle bot, which needs way less precision.

16

A ME lab class taught more about strain gauge application and theory more than my EE classes.

What orientation on the inner surface of a cantilevered tube is going to strain sensibly with a radial load?

Use 4 gauges in a full bridge, appropriately positioned to detect the strain of interest.

17

Just detect when a load is applied or also measure the load?

18

The radial load will be always perpendicular so there will only be tension and compression along the tube. I currently have a rosette as my strain gauge and the plan was to get a load sensor combinator to be able to only have to use the rosette vs four gauges.

19

Merely just to detect that there is a load, like a deflection in the tube but to a precision of as close to 0.01in and hopefully a little lower.

20

What kind?
They can 2, 3 or more gauges oriented in different directions.