Learn how to interface a monochrome LCD module with STM32 microcontrollers using SPI or parallel communication. Includes circuit diagrams, STM32 HAL code, troubleshooting tips, and application examples.
Introduction: Why Use a Monochrome LCD Display
Monochrome LCDs remain essential in the world of embedded electronics. Despite newer OLED and TFT technologies, monochrome LCD modules are still preferred for industrial, medical, and embedded applications due to their stability, efficiency, and readability.
If you’re developing with the STM32 microcontroller family, integrating a monochrome LCD can enhance your project’s visual interface while keeping costs low.
Advantages of Monochrome LCDs
- Low power consumption for battery-based systems
- Excellent sunlight readability
- Long operational life (>50,000 hours)
- Cost-effective for mass production
Common Applications
- Industrial meters and controllers
- Portable medical devices
- DIY electronics and hobby projects
- Measurement and diagnostic tools
Understanding Monochrome LCD Technology
A monochrome LCD (Liquid Crystal Display) manipulates light polarization using liquid crystal molecules. Applying voltage changes alignment, creating visible dark and light segments.
Character vs. Graphic LCD
- Character LCDs (e.g., 1602, 2004): Predefined character grids
- Graphic LCDs (e.g., 128×64): Pixel-level control for custom graphics
Important Specifications
| Parameter | Description |
|---|---|
| Resolution | 128×64, 240×128, etc. |
| Interface | SPI, I2C, Parallel |
| Voltage | 3.3V or 5V |
| Controller IC | ST7565, RA8835, KS0108 |
| Backlight | LED or EL |
| Viewing Mode | Positive/Negative |
STM32 and LCD Communication Basics
Supported Interfaces
STM32 microcontrollers support multiple LCD interfaces:
- SPI (Serial Peripheral Interface): Fast and uses few pins
- I2C (Inter-Integrated Circuit): Easy wiring but slower
- Parallel: Fastest for high-resolution displays
Selecting the Right Interface
For most small monochrome modules, SPI is the optimal balance between simplicity and speed.
Hardware Setup: Connecting LCD to STM32
Here’s a common SPI connection for 128×64 LCD modules:
| STM32 Pin | LCD Pin | Function |
|---|---|---|
| PA5 | SCLK | Clock |
| PA7 | MOSI | Data Line |
| PA4 | CS | Chip Select |
| PA3 | A0 | Command/Data |
| 3.3V | VCC | Power |
| GND | GND | Ground |
Tip: Always check your LCD’s datasheet. Some modules use reversed A0/CS logic or require reset pins.
Wiring and Stability
- Use short wires for SPI lines
- Add 0.1µF decoupling capacitors near the LCD power pins
- For backlight LEDs, include a resistor (typically 100Ω)
For circuit references, check Hackaday LCD Projects to see real-world STM32 + LCD builds.
Software Setup and LCD Initialization
Command and Data Transmission
The STM32 communicates with the LCD controller via SPI commands and data bytes.
Example STM32 HAL Code:
void LCD_SendCommand(uint8_t cmd) {
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_3, GPIO_PIN_RESET); // A0 = 0
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_RESET); // CS = 0
HAL_SPI_Transmit(&hspi1, &cmd, 1, HAL_MAX_DELAY);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET);
}
void LCD_SendData(uint8_t data) {
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_3, GPIO_PIN_SET); // A0 = 1
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_RESET);
HAL_SPI_Transmit(&hspi1, &data, 1, HAL_MAX_DELAY);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET);
}
Initialization Sequence
Typical sequence for ST7565 controllers:
- Power ON delay (40ms)
- Function set command
- Display ON
- Set contrast
- Clear display RAM
Common Issues and Troubleshooting
| Problem | Likely Cause | Solution |
|---|---|---|
| No display | Missing contrast voltage | Adjust V0 or check resistor divider |
| Garbled pixels | Wrong init sequence | Match controller timing |
| Flicker | Poor grounding | Add decoupling capacitors |
| Dim display | LED backlight undervoltage | Verify power lines |
Real-World Applications
Industrial Systems
Used in control panels, automation units, and diagnostic interfaces.
Their reliability makes them ideal for rugged environments.
Medical Devices
Monochrome LCDs are used in portable medical instruments for stable, EMI-resistant display performance.
DIY & Educational Projects
Popular among makers for Arduino/STM32-based data displays and custom tools.
For inspiration, check Hackaday’s embedded projects and EEVblog community builds.
FAQs: STM32 Monochrome LCD Interface
Q1: Can I use I2C instead of SPI?
Yes, if your module supports it—but expect slower updates.
Q2: How do I adjust contrast?
Either via software commands or using an external resistor network.
Q3: Why is nothing showing after powering up?
Double-check initialization sequence and ensure correct voltage levels.
Q4: Can I display images or logos?
Yes, on graphic LCDs (e.g., 128×64), by writing bitmap data to the buffer.
Q5: How to save power?
Use PWM dimming for backlight and partial refresh for static content.
Conclusion
Integrating a monochrome LCD with STM32 is straightforward once you understand its hardware connections and command logic. With proper grounding, initialization, and code handling, these displays can serve as reliable human-machine interfaces for industrial and embedded devices.
