How to Use LCD Display 128x64 (ST7920): Examples, Pinouts, and Specs

The LCD Display 128x64 (ST7920) is a graphical LCD module with a resolution of 128x64 pixels. It is widely used in embedded systems for displaying text, graphics, and images. The display is powered by the ST7920 controller, which supports both parallel and serial (SPI) communication, making it versatile and easy to integrate into various microcontroller-based projects.

• User interfaces for embedded systems
• Displaying sensor data in IoT devices
• Graphical representations in industrial control systems
• Educational and hobbyist projects
• Portable devices requiring low-power graphical displays

1. Power Supply: Connect the VDD pin to a 5V power source and VSS to ground.
2. Contrast Adjustment: Use a 10kΩ potentiometer connected to the VO pin to adjust the display contrast.
3. Interface Selection: Set the PSB pin to 1 for parallel mode or 0 for serial mode.
4. Backlight: Connect the A and K pins to a 5V power source and ground, respectively, to enable the backlight.
5. Microcontroller Connection:
   • For parallel mode, connect the data bus (DB0-DB7 or DB4-DB7 for 4-bit mode) and control pins (RS, RW, E) to the microcontroller.
   • For serial mode, connect RS, RW (SCK), and E (SID) to the microcontroller.

• Ensure the power supply voltage is within the specified range to avoid damaging the display.
• Use decoupling capacitors (e.g., 0.1µF) near the power pins to reduce noise.
• Avoid leaving unused data pins floating; tie them to ground if not used.
• For SPI mode, ensure the microcontroller supports the required clock speed for proper communication.

#include <U8g2lib.h>

// Initialize the display in SPI mode
// U8G2_ST7920_128X64_F_SW_SPI: Constructor for ST7920 in software SPI mode
U8G2_ST7920_128X64_F_SW_SPI u8g2(U8G2_R0, /* clock=*/ 13, /* data=*/ 11, /* cs=*/ 10);

void setup() {
  u8g2.begin(); // Initialize the display
}

void loop() {
  u8g2.clearBuffer(); // Clear the display buffer
  u8g2.setFont(u8g2_font_ncenB08_tr); // Set font
  u8g2.drawStr(0, 10, "Hello, World!"); // Draw text at (0, 10)
  u8g2.sendBuffer(); // Send buffer to display
  delay(1000); // Wait for 1 second
}

1. Display Not Turning On:

   • Verify the power supply connections (VDD and VSS).
   • Check the backlight connections (A and K).

2. No Text or Graphics Displayed:

   • Ensure the contrast is properly adjusted using the potentiometer on the VO pin.
   • Verify the communication mode (parallel or serial) matches the microcontroller configuration.

3. Flickering or Unstable Display:

   • Add decoupling capacitors near the power pins to reduce noise.
   • Check for loose or poor connections in the circuit.

4. Incorrect or Garbled Output:

   • Ensure the data and control pins are correctly connected to the microcontroller.
   • Double-check the initialization code and communication settings.

Q: Can I use the display with a 3.3V microcontroller?
A: The display requires a 5V power supply. Use a level shifter for 3.3V microcontrollers to safely interface with the display.

Q: How do I switch between 8-bit and 4-bit parallel modes?
A: In 4-bit mode, only DB4-DB7 are used for data transfer. Leave DB0-DB3 unconnected or tied to ground.

Q: Is the backlight mandatory for operation?
A: No, the backlight is optional. However, it improves visibility in low-light conditions.