How to Use ST7796S_3_5: Examples, Pinouts, and Specs

The ST7796S_3_5 is a TFT LCD display driver IC designed for 3.5-inch screens, offering a resolution of 320x480 pixels. It supports multiple color depths (up to 16.7M colors) and various communication interfaces, including SPI, MCU parallel, and RGB interfaces. This makes it a versatile choice for embedded systems, graphical user interfaces, and portable devices.

• Embedded systems with graphical user interfaces
• Industrial control panels
• Portable devices and handheld instruments
• Consumer electronics such as smart home displays
• Educational and hobbyist projects (e.g., Arduino and Raspberry Pi)

The ST7796S_3_5 typically comes with a 40-pin interface. Below is a table of the most commonly used pins:

Note: The exact pinout may vary depending on the specific module or breakout board. Always refer to the datasheet or module documentation for precise details.

1. Power Supply: Connect the VCC pin to a 3.3V power source and the GND pin to ground. Ensure the power supply is stable and within the specified range.
2. Backlight: Connect the LED+ pin to a 3.3V or 5V source through a suitable current-limiting resistor. Connect LED- to ground.
3. Interface Selection: Choose the communication interface (SPI, MCU parallel, or RGB) based on your application. For SPI, connect the CS, RESET, DC/RS, SDI/MOSI, and SCK pins to your microcontroller.
4. Initialization: Use the appropriate initialization sequence for the ST7796S_3_5. This typically involves sending a series of commands to configure the display settings (e.g., resolution, color depth, and orientation).

• Voltage Levels: Ensure all signal lines are within the voltage range of the display (typically 3.3V). Use level shifters if interfacing with a 5V microcontroller.
• Backlight Current: Use a resistor to limit the current through the backlight LEDs to prevent damage.
• Reset Pin: Always initialize the display by toggling the RESET pin low for at least 10ms before sending commands.
• Decoupling Capacitors: Place decoupling capacitors (e.g., 0.1µF) near the power pins to reduce noise and ensure stable operation.

Below is an example of how to connect the ST7796S_3_5 to an Arduino UNO using SPI mode:

#include <Adafruit_GFX.h>    // Graphics library
#include <Adafruit_ST7796S.h> // ST7796S driver library

// Define pins for the display
#define TFT_CS   10  // Chip Select
#define TFT_RST  9   // Reset
#define TFT_DC   8   // Data/Command

// Create an instance of the display driver
Adafruit_ST7796S tft = Adafruit_ST7796S(TFT_CS, TFT_DC, TFT_RST);

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

  // Set rotation (0-3)
  tft.setRotation(1);

  // Fill the screen with a color
  tft.fillScreen(ST77XX_BLUE);

  // Draw some text
  tft.setTextColor(ST77XX_WHITE);
  tft.setTextSize(2);
  tft.setCursor(10, 10);
  tft.println("Hello, ST7796S!");
}

void loop() {
  // Nothing to do here
}

Note: Ensure you have the required libraries installed in your Arduino IDE. You can install the Adafruit_GFX and Adafruit_ST7796S libraries via the Library Manager.

1. Display Not Turning On

   • Cause: Incorrect power supply or loose connections.
   • Solution: Verify that the VCC and GND pins are properly connected and the power supply is within the specified range.

2. No Image on the Screen

   • Cause: Incorrect initialization or communication settings.
   • Solution: Double-check the wiring and ensure the initialization sequence matches the ST7796S datasheet.

3. Flickering or Dim Backlight

   • Cause: Insufficient current to the backlight LEDs.
   • Solution: Use a lower-value resistor for the LED+ pin or check the power supply.

4. Colors Appear Incorrect

   • Cause: Incorrect color depth or data format.
   • Solution: Ensure the display is configured for the correct color depth (e.g., 16-bit or 24-bit).

• Can I use the ST7796S_3_5 with a 5V microcontroller?

  • Yes, but you will need level shifters to convert the 5V logic signals to 3.3V.

• What is the maximum refresh rate of the display?

  • The refresh rate depends on the interface and clock speed but typically supports up to 60Hz.

• Is the ST7796S_3_5 compatible with Raspberry Pi?

  • Yes, it can be used with Raspberry Pi via SPI or parallel interfaces. Ensure you use the appropriate driver and wiring.

• Can I use the display in outdoor environments?

  • The display is not sunlight-readable and is best suited for indoor use. However, it can operate in temperatures ranging from -20°C to 70°C.