DIYmall HX711 Weight Weighing Load Cell Conversion Module - Instruction Manual

1. Introduction

The DIYmall HX711 module is a 24-bit high-precision analog-to-digital converter (ADC) designed specifically for weighing scales and industrial control applications. It interfaces directly with a bridge sensor (such as a load cell) to convert analog weight signals into digital data for microcontrollers like Arduino. This module features two selectable differential input channels and an internal 128x programmable gain amplifier, offering high precision and low cost for various measurement projects.

2. Product Overview

This section provides a visual and functional overview of the HX711 module.

Figure 2.1: Two HX711 load cell amplifier modules, each with pin headers for connection.

Figure 2.2: Close-up view of the HX711 module, highlighting the HX711 chip and pin labels (E+, E-, A+, A-, B+, B-, GND, DT, SCK, VCC).

Figure 2.3: Bottom view of the HX711 module, showing solder points for pin headers.

3. Specifications

Figure 3.1: Dimensions of the HX711 module (approximately 35mm x 20mm).

4. Setup

To set up the HX711 module, you will need a load cell and a microcontroller (e.g., Arduino). The module acts as an interface between the load cell and the microcontroller.

4.1. Load Cell Connection

Connect your load cell to the HX711 module using the E+, E-, A+, A-, B+, B- pins. Most load cells are 4-wire (Red, Black, White, Green) and form a Wheatstone bridge configuration.

• E+ (Excitation+): Connect to the Red wire of the load cell.
• E- (Excitation-): Connect to the Black wire of the load cell.
• A+ (Output+): Connect to the White wire of the load cell.
• A- (Output-): Connect to the Green wire of the load cell.
• B+, B-: These are for a second differential input channel, typically unused for a single load cell.

Figure 4.1: Standard Wheatstone bridge load cell wiring to the HX711 module.

4.2. Microcontroller Connection (e.g., Arduino)

Connect the HX711 module to your microcontroller as follows:

• VCC: Connect to 5V or 3.3V power supply from your microcontroller.
• GND: Connect to the Ground pin of your microcontroller.
• SCK (Serial Clock): Connect to a digital output pin on your microcontroller.
• DT (Data Output): Connect to a digital input pin on your microcontroller.

Figure 4.2: Example wiring of the HX711 module with a load cell and an Arduino microcontroller.

5. Operation

Once wired, the HX711 module requires software to communicate with the microcontroller and interpret the weight data.

5.1. Software Library

For Arduino, dedicated libraries are available (e.g., HX711 library by bogde) that simplify communication. These libraries handle the serial communication protocol (SCK and DT pins) and provide functions to read raw data, set calibration factors, and obtain weight readings.

5.2. Calibration

Calibration is crucial for accurate weight measurements. This typically involves:

1. Reading the raw value with no weight on the load cell (tare).
2. Placing a known weight on the load cell and reading the corresponding raw value.
3. Calculating a calibration factor based on the difference between the tared reading and the known weight reading.
4. Applying this factor to subsequent raw readings to convert them into actual weight units.

5.3. Sampling Rate

The HX711 operates at a default sampling rate of 10 samples per second (SPS). This can be increased to 80 SPS by modifying the module (e.g., lifting pin 15 and connecting it to pin 16, as per the HX711 datasheet). Refer to the HX711 datasheet for detailed instructions on modifying the sampling rate.

6. Maintenance

The HX711 module is a robust electronic component, but proper handling and care ensure its longevity and reliable performance.

• Environmental Conditions: Operate the module within its specified temperature and humidity ranges. Avoid extreme conditions.
• Cleanliness: Keep the module free from dust, dirt, and moisture. Use a soft, dry brush or compressed air for cleaning if necessary.
• Static Discharge: Always handle the module with anti-static precautions to prevent damage from electrostatic discharge (ESD).
• Physical Protection: Avoid physical stress or impact to the module. Ensure it is securely mounted in your project enclosure.
• Power Supply: Provide a stable and clean power supply within the recommended voltage range (typically 2.7V to 5.5V).

7. Troubleshooting

If you encounter issues with your HX711 module, consider the following common troubleshooting steps:

• Unstable Readings or Drifting Output: Some HX711 board designs may have an issue where the E- pin is not properly connected to the analog ground. This can cause instability. A common fix is to connect the E- pin directly to the GND pin on the 4-pin header. This ensures the bridge excitation is properly referenced to ground.
• No Readings or Incorrect Data:
• Verify all wiring connections are secure and correct, especially VCC, GND, SCK, and DT.
• Ensure the load cell is correctly wired to the E+, E-, A+, A- pins.
• Check your microcontroller code and ensure the HX711 library is correctly initialized and used.
• Confirm the power supply voltage is stable and within the module's operating range.
• Module Not Responding:
• Double-check power and ground connections. Incorrect polarity can damage the module.
• Ensure the SCK and DT pins are connected to appropriate digital pins on your microcontroller and are not conflicting with other components.
• Noise in Readings:
• Use shielded cables for load cell connections, especially in noisy electrical environments.
• Ensure proper grounding of your entire system.
• Add decoupling capacitors near the HX711's VCC and GND pins if not already present on the board.
• Difficulty with Soldering Pins: The pins on one side of the module may be short, making soldering challenging. Use appropriate soldering techniques and ensure good connections to prevent intermittent issues.

8. Warranty and Support

For warranty information or technical support, please refer to the DIYmall official website or contact your retailer. Keep your purchase receipt as proof of purchase.