How to make an electronic scale with STM32?

Creating an electronic scale using an STM32 microcontroller involves integrating a load cell, an analog-to-digital converter (ADC), and an STM32 microcontroller to measure weight and display the result. Below is a step-by-step guide to help you build your electronic scale:

Components Required

1. STM32 Microcontroller (e.g., STM32F103C8T6 or any STM32 with ADC).

2. Load Cell (e.g., HX711 load cell, commonly used in weight measurement).

3. HX711 Amplifier Module (for amplifying the load cell signal).

4. Display (e.g., LCD, OLED, or 7-segment display to show the weight).

5. Breadboard and Jumper Wires.

6. Power Supply (e.g., 5V or 3.3V, depending on your components).

7. Push Buttons (optional, for calibration or tare functionality).

8. Resistors, Capacitors, and Other Basic Components.

Step 1: Understand the Load Cell and HX711 Module

• A load cell is a transducer that converts force (weight) into an electrical signal.

• The HX711 module amplifies the small signal from the load cell and provides a digital output to the STM32.

Step 2: Circuit Connections

1. Load Cell to HX711:

   • Connect the load cell's wires to the HX711 module:

     • Red wire: E+

     • Black wire: E-

     • White wire: A-

     • Green wire: A+

2. HX711 to STM32:

   • Connect the HX711 module to the STM32:

     • VCC: 5V or 3.3V (depending on the module).

     • GND: Ground.

     • DT (Data): Connect to a GPIO pin (e.g., PA0).

     • SCK (Clock): Connect to another GPIO pin (e.g., PA1).

3. Display to STM32:

   • Connect the display (e.g., LCD or OLED) to the STM32 using I2C, SPI, or GPIO pins, depending on the display type.

4. Power Supply:

   • Ensure all components are properly powered (STM32, HX711, and display).

Step 3: Write the STM32 Code

Use STM32CubeIDE or any other IDE to write the firmware for the STM32.

1. Initialize Peripherals:

   • Set up GPIO pins for HX711 (DT and SCK).

   • Configure the display interface (I2C, SPI, or GPIO).

2. Read Data from HX711:

   • Implement the HX711 communication protocol to read the digital weight data.

   • Example code snippet for reading data:

     c

      

     uint32_t HX711_Read() {
         uint32_t data = 0;
         HAL_GPIO_WritePin(SCK_GPIO_Port, SCK_Pin, GPIO_PIN_RESET); // Pull SCK low
         while (HAL_GPIO_ReadPin(DT_GPIO_Port, DT_Pin) == GPIO_PIN_SET); // Wait for DT to go low
         for (int i = 0; i < 24; i++) {
             HAL_GPIO_WritePin(SCK_GPIO_Port, SCK_Pin, GPIO_PIN_SET); // Pulse SCK
             data <<= 1;
             if (HAL_GPIO_ReadPin(DT_GPIO_Port, DT_Pin) == GPIO_PIN_SET) {
                 data++;
             }
             HAL_GPIO_WritePin(SCK_GPIO_Port, SCK_Pin, GPIO_PIN_RESET); // Pull SCK low
         }
         HAL_GPIO_WritePin(SCK_GPIO_Port, SCK_Pin, GPIO_PIN_SET); // 25th pulse to set gain
         HAL_GPIO_WritePin(SCK_GPIO_Port, SCK_Pin, GPIO_PIN_RESET);
         return data ^ 0x800000; // Convert to signed value
     }

3. Convert Raw Data to Weight:

   • Calibrate the load cell to convert raw ADC values to weight (e.g., grams or kilograms).

   • Example:

     c

      

     float raw_to_weight(uint32_t raw_value) {
         float calibration_factor = -7050.0; // Adjust based on calibration
         return (raw_value / calibration_factor);
     }

4. Display the Weight:

   • Send the calculated weight to the display.

   • Example for an LCD:

     c

      

     void display_weight(float weight) {
         char buffer[16];
         sprintf(buffer, "Weight: %.2f g", weight);
         LCD_Print(buffer);
     }

5. Add Calibration and Tare Functionality:

   • Use push buttons to calibrate the scale or tare (zero) the weight.

Step 4: Calibrate the Scale

1. Place a known weight on the load cell.

2. Adjust the calibration factor in the code until the displayed weight matches the known weight.

Step 5: Test and Refine

• Test the scale with different weights to ensure accuracy.

• Refine the code and calibration as needed.

Example Workflow

1. Power on the system.

2. Place an object on the load cell.

3. The STM32 reads the data from the HX711.

4. The weight is calculated and displayed on the screen.

Additional Tips

• Use a stable power supply to avoid fluctuations in readings.

• Ensure the load cell is properly mounted and balanced.

• Add filtering (e.g., moving average) to smooth out noisy readings.

By following these steps, you can build a functional electronic scale using an STM32 microcontroller. Let me know if you need further assistance!