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# HX711 Load Cell Amplifier with an Arduino Uno

On an Arduino Uno the HX711 module runs from the 5V pin, so DT's high is 5 V and the chip gets the 5 V supply its datasheet uses for its ±20 mV full scale at gain 128. DT and SCK sit on D3 and D2, two ordinary digital pins the library bit-bangs.

## Wiring

| HX711 Load Cell Amplifier | Arduino Uno | Note |
| --- | --- | --- |
| VCC | 5V |  |
| GND | GND |  |
| DT | D3 |  |
| SCK | D2 |  |

## What to know on the Arduino Uno

- Channel A's full scale is ±20 mV at gain 128 with AVDD = 5 V. The module's excitation regulator needs its output at least 100 mV below VSUP, a headroom the Uno's 5V supply provides. (Avia HX711 datasheet V2.0, pp. 1, 3, 4)
- Holding SCK high for more than 60 µs powers the HX711 down. On the Uno a long interrupt in the middle of a read, such as SoftwareSerial receiving a byte, can stretch a clock pulse that long and corrupt the reading, so avoid SoftwareSerial traffic during scale.get_units(). (Avia HX711 datasheet V2.0, p. 5)
- At the module's 10 samples per second the first valid reading arrives 400 ms after power-up, which is why setup() waits for is_ready() before taring, and why get_units(5) takes about half a second on the Uno. (Avia HX711 datasheet V2.0, pp. 1, 3)
- The load cell's output is millivolts, far below one step of the Uno's own ADC (about 4.9 mV on 5 V), which is why it goes through the HX711 and never to an analog pin. (Microchip ATmega328P datasheet DS40002061B, p. 2)

## Code

Libraries: robtillaart/HX711

```cpp
// HX711 Load Cell Amplifier on Arduino Uno: wiring and a free simulation at https://www.tinkered.ai/components/hx711-module/arduino-uno
#include "HX711.h"

const int DT_PIN = 3;    // HX711 DT (DOUT)
const int SCK_PIN = 2;   // HX711 SCK
// counts per gram: about 430 for a 5 kg bar (2150 at 1 kg, 215 at 10 kg); calibrate with a known weight
const float CALIBRATION = 430.0;

HX711 scale;

void setup() {
  Serial.begin(9600);
  scale.begin(DT_PIN, SCK_PIN);
  Serial.println("HX711 scale");
  while (!scale.is_ready()) delay(10);   // its first reading comes 0.4 s after power-up
  scale.set_scale(CALIBRATION);
  scale.tare(10);                        // the empty scale's zero, averaged
  Serial.println("Tared: put a weight on it");
}

void loop() {
  if (scale.is_ready()) {
    float grams = scale.get_units(5);    // the average of 5 readings, tared and scaled
    Serial.print("Weight: ");
    Serial.print(grams, 1);
    Serial.println(" g");
  }
  delay(500);
}
```

Compiled for arduino:avr:uno on 2026-10-30.

## Questions

### Can I connect the HX711 to the Arduino Uno's 5V?

Yes. The HX711 runs from 2.6 V to 5.5 V (Avia datasheet, p. 1), and on 5V its DT output matches the Uno's logic. 5 V is also the supply at which the datasheet gives the ±20 mV full scale.

### Why can't I read a load cell with analogRead() on the Uno?

A load cell gives about 1 mV per volt at full load, while one step of the Uno's 10-bit ADC is about 4.9 mV. The HX711's gain of 128 and 24-bit ADC resolve it.

### Why are my HX711 readings occasionally wrong on the Uno?

If SCK stays high more than 60 µs the chip powers down (Avia datasheet, p. 5). Interrupt-heavy code, SoftwareSerial in particular, can stretch a clock pulse that long; read the scale when no other serial traffic is running.

## More

- [HX711 Load Cell Amplifier reference](https://www.tinkered.ai/components/hx711-module.md): pinout, specs, rules and common mistakes

## Try it

Tinkered simulates the HX711 Load Cell Amplifier on the Arduino Uno in the browser, with this wiring and code, free: https://www.tinkered.ai/components/hx711-module/arduino-uno