How to Use SparkFun Load Cell Amplifier - HX711: Examples, Pinouts, and Specs

The SparkFun Load Cell Amplifier - HX711 is a small breakout board designed to interface directly with load cells. Load cells are transducers that convert force into an electrical signal, and the HX711 is a precision 24-bit analog-to-digital converter (ADC) designed for weigh scales and industrial control applications to interface directly with a bridge sensor. This module is ideal for applications such as measuring weight, creating scales, and industrial process control where accurate weight measurements are required.

• Digital weighing machines
• Kitchen and luggage scales
• Industrial mixing and batching systems
• Force sensing in robotics and embedded systems

• Voltage: 2.6V to 5.5V DC
• Current: < 1.5mA
• Selectable 10SPS or 80SPS output data rate
• Selectable gain of 32, 64 and 128
• On-chip power supply regulator for load-cell and ADC analog power supply
• On-chip oscillator requiring no external component with optional external crystal

1. Connecting the Load Cell:

   • Connect the load cell wires to the HX711 module according to the load cell's datasheet. Typically, the red wire goes to E+, black to E-, and the white and green wires to A+ and A-, respectively.

2. Powering the Module:

   • Supply the HX711 with a clean and stable voltage between 2.6V and 5.5V.

3. Interfacing with a Microcontroller:

   • Connect the DT and SCK pins of the HX711 to digital pins on your microcontroller, such as an Arduino UNO.

• Use a stable power supply to avoid fluctuations in readings.
• Keep the wires between the load cell and HX711 as short as possible to minimize noise.
• Calibrate the load cell with known weights to ensure accurate measurements.
• Avoid physical shocks and vibrations that can affect the readings.

#include "HX711.h"

// HX711 circuit wiring
const int LOADCELL_DOUT_PIN = 3;
const int LOADCELL_SCK_PIN = 2;

HX711 scale;

void setup() {
  Serial.begin(9600);
  scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
}

void loop() {
  if (scale.is_ready()) {
    long reading = scale.read();
    Serial.print("Reading: ");
    Serial.println(reading);
  } else {
    Serial.println("HX711 not found.");
  }
  delay(1000);
}

• Inaccurate Readings: Ensure the load cell is properly calibrated and that the module is powered with a stable voltage.
• No Readings: Check all connections, including the load cell wires and the connections to the microcontroller.
• Fluctuating Readings: This can be due to electrical noise or vibrations. Ensure the setup is stable and away from sources of interference.

• Calibration: Use known weights to calibrate the load cell. Adjust the calibration factor in the code accordingly.
• Stable Setup: Mount the load cell and HX711 on a firm surface to minimize vibrations.
• Shielding: Use shielded cables for connections and keep them short to reduce noise.

Q: Can I use multiple load cells with one HX711? A: Yes, but all load cells must be identical and wired in parallel, effectively creating a single load cell.

Q: How do I calibrate my load cell? A: Apply known weights and adjust the calibration factor in your code until the readings match the applied weights.

Q: What is the maximum rate at which I can get readings? A: The HX711 can be set to 10 or 80 samples per second (SPS).

Q: Can I use the HX711 for applications other than weight measurement? A: Yes, the HX711 can be used for any application that requires precise measurement of a resistive bridge sensor, such as pressure sensors or strain gauges.