¶ Backlight PWM Control
This sample program demonstrates how to use the ESP32's LEDC (LED Controller) PWM functionality to control the backlight brightness of a TFT LCD screen. By touching the slider on the screen, users can adjust the backlight brightness in real-time, achieving stepless dimming from 0 (off) to 255 (maximum brightness).
¶ Code Explanation
This sample code is based on the ESP32-WROOM-32E development board, using the TFT_eSPI library to drive the ILI9341 LCD screen and touch functionality.
¶ Basic Configuration (Brief)
The following introduces the basic configuration of the program:
- Library Introduction: Includes
TFT_eSPI.h(core graphics driver library) andTFT_Touch.h(touch driver library) for LCD display and touch detection functionality. - Pin Definition:
BACKLIGHT_PIN(GPIO 21): Backlight control pin, outputs PWM signalRTP_DOUT(GPIO 39),RTP_DIN(GPIO 32),RTP_SCK(GPIO 25),RTP_CS(GPIO 33): Touch screen interface pins
- PWM Parameter Settings:
freq = 2000: PWM frequency of 2000 Hzchannel = 0: Uses LEDC channel 0resolution = 8: 8-bit resolution, range 0-255 (256 brightness levels total)
- Object Instantiation: Creates
TFT_eSPI my_lcdandTFT_Touch my_touchobjects for LCD display and touch detection respectively.
¶ Detailed Explanation of setup() Function
The setup() function completes the initialization of the serial port, LCD screen, and touch screen, and draws the UI elements of the backlight control interface.
void setup()
{
Serial.begin(115200);
my_lcd.begin();
my_lcd.setRotation(1);
my_touch.setCal(495, 3398, 721, 3448, 320, 240, 1);
my_lcd.fillScreen(TFT_WHITE);
my_lcd.setTextColor(TFT_BLACK, TFT_WHITE);
my_lcd.setTextSize(2);
my_lcd.setCursor(my_lcd.width()/2-150, 160);
my_lcd.println("0");
my_lcd.setCursor(my_lcd.width()/2+110, 160);
my_lcd.println("255");
my_lcd.fillRoundRect(my_lcd.width()/2-138, 130, 276, 21,10,0x07FF);
my_lcd.fillCircle(my_lcd.width()/2+128, 140,10,TFT_MAGENTA);
my_lcd.setTextColor(TFT_RED);
my_lcd.drawNumber(255, my_lcd.width()/2-15, 65,2);
ledcAttachChannel(BACKLIGHT_PIN, freq, resolution, channel);
ledcWrite(BACKLIGHT_PIN, 255);
}
¶ Serial Port Initialization
Serial.begin(115200);
Sets the serial baud rate to 115200 for debugging information output.
¶ LCD Initialization and Rotation Setting
my_lcd.begin();
my_lcd.setRotation(1);
my_lcd.begin(): Initializes the TFT_eSPI library, configures the SPI interface and LCD driver chipmy_lcd.setRotation(1): Sets the screen to landscape display mode (rotated 90°)
¶ Touch Screen Calibration
my_touch.setCal(495, 3398, 721, 3448, 320, 240, 1);
Sets touch calibration parameters to map the touch screen's raw analog coordinates to screen pixel coordinates. The parameters (495, 3398, 721, 3448, 320, 240, 1) correspond to X-axis minimum, X-axis maximum, Y-axis minimum, Y-axis maximum, screen width, screen height, and rotation direction respectively.
¶ UI Interface Drawing
my_lcd.fillScreen(TFT_WHITE);
my_lcd.setTextColor(TFT_BLACK, TFT_WHITE);
my_lcd.setTextSize(2);
my_lcd.setCursor(my_lcd.width()/2-150, 160);
my_lcd.println("0");
my_lcd.setCursor(my_lcd.width()/2+110, 160);
my_lcd.println("255");
my_lcd.fillRoundRect(my_lcd.width()/2-138, 130, 276, 21,10,0x07FF);
my_lcd.fillCircle(my_lcd.width()/2+128, 140,10,TFT_MAGENTA);
my_lcd.setTextColor(TFT_RED);
my_lcd.drawNumber(255, my_lcd.width()/2-15, 65,2);
Sequentially draws the following UI elements:
- White Background Fill:
fillScreen(TFT_WHITE)sets the screen background to white - Scale Labels: Displays "0" and "255" at both ends of the slider to indicate the brightness range
- Slider Track: Draws a 276×21 pixel rounded rectangle as the slider track in cyan (0x07FF)
- Slider Thumb: Draws a magenta circular slider thumb with a 10-pixel radius at the rightmost end of the track (initial position corresponding to brightness 255)
- Brightness Value Display: Displays the current brightness value 255 centered at the top of the screen (red font)
¶ PWM Initialization and Initial Backlight Setting
ledcAttachChannel(BACKLIGHT_PIN, freq, resolution, channel);
ledcWrite(BACKLIGHT_PIN, 255);
ledcAttachChannel(): Binds GPIO 21 to LEDC channel 0, configured with 2000 Hz frequency and 8-bit resolutionledcWrite(BACKLIGHT_PIN, 255): Sets the initial backlight brightness to 255 (maximum)
¶ Detailed Explanation of loop() Function
The loop() function is the main loop of the Arduino program, running repeatedly after setup() completes. It continuously detects touch input and dynamically adjusts the backlight brightness based on the touch position.
void loop()
{
uint16_t t_x = 0, t_y = 0; // Store touch coordinates
if(my_touch.Pressed())
{
t_x = my_touch.X();
t_y = my_touch.Y();
if((t_x>=my_lcd.width()/2-128)&&(t_x<my_lcd.width()/2+128)&&t_y > 129&&t_y < 149)
{
my_lcd.setTextColor(TFT_RED, TFT_WHITE);
my_lcd.fillRoundRect(t_x-10, 130, my_lcd.width()/2+138-t_x+10, 21,10,0x8430);
my_lcd.fillRoundRect(my_lcd.width()/2-138, 130, t_x-my_lcd.width()/2+148, 21,10,0x07FF);
my_lcd.fillCircle(t_x, 140,10,TFT_MAGENTA);
my_lcd.setTextPadding(50);
my_lcd.drawNumber((long)t_x-(my_lcd.width()/2-128), my_lcd.width()/2-15, 65,2);
ledcWrite(BACKLIGHT_PIN, t_x-(my_lcd.width()/2-128));
}
}
}
¶ Touch Detection
uint16_t t_x = 0, t_y = 0;
if(my_touch.Pressed())
{
t_x = my_touch.X();
t_y = my_touch.Y();
- Declares
t_xandt_yvariables to store touch coordinates my_touch.Pressed(): Detects whether the screen is being touchedmy_touch.X()andmy_touch.Y(): Gets the X and Y coordinates of the touch point
¶ Touch Area Validation
if((t_x>=my_lcd.width()/2-128)&&(t_x<my_lcd.width()/2+128)&&t_y > 129&&t_y < 149)
Determines whether the touch point is within the slider range:
- X direction is limited to ±128 pixels from the screen center (i.e., a 256-pixel wide slider)
- Y direction is limited to between 129-149 pixels (i.e., the vertical position of the slider track)
Only when the touch point is within the slider area will the brightness adjustment operation be executed.
¶ UI Update
my_lcd.setTextColor(TFT_RED, TFT_WHITE);
my_lcd.fillRoundRect(t_x-10, 130, my_lcd.width()/2+138-t_x+10, 21,10,0x8430);
my_lcd.fillRoundRect(my_lcd.width()/2-138, 130, t_x-my_lcd.width()/2+148, 21,10,0x07FF);
my_lcd.fillCircle(t_x, 140,10,TFT_MAGENTA);
my_lcd.setTextPadding(50);
my_lcd.drawNumber((long)t_x-(my_lcd.width()/2-128), my_lcd.width()/2-15, 65,2);
Updates the interface display based on the touch position:
- Right Fill: Draws a gray-blue rounded rectangle (0x8430) from the slider position to the right end of the track, indicating the "empty" area
- Left Fill: Draws a cyan rounded rectangle (0x07FF) from the left end of the track to the slider position, indicating the current brightness level
- Slider Thumb: Draws a magenta circular slider thumb at the touch point position
- Value Update: Converts the touch X coordinate to a brightness value (0-255 range) and displays it at the top of the screen
¶ Backlight Brightness Adjustment
ledcWrite(BACKLIGHT_PIN, t_x-(my_lcd.width()/2-128));
Maps the touch position to a PWM duty cycle:
t_x - (my_lcd.width()/2 - 128)converts the touch X coordinate to a 0-255 brightness value- Calls
ledcWrite()to set the PWM output of the backlight pin, achieving real-time brightness adjustment
¶ Summary
This sample program implements touch-screen controlled backlight brightness through the following steps:
- Initialization: Configures the serial port, LCD screen, touch screen, and LEDC PWM module, and draws the UI interface
- Touch Detection: Continuously detects touch input and determines whether the touch position is within the slider range
- Brightness Adjustment: Calculates the target brightness value based on the touch position, updates the UI display, and sets the PWM duty cycle
The key functions used in the program include:
my_lcd.begin(): Initializes the TFT_eSPI library and LCD screenmy_lcd.setRotation(): Sets the screen rotation directionmy_touch.setCal(): Configures touch screen calibration parametersmy_lcd.fillScreen(): Fills the entire screen with a specified colormy_lcd.fillRoundRect(): Draws a filled rounded rectanglemy_lcd.fillCircle(): Draws a filled circlemy_lcd.drawNumber(): Draws a number at a specified positionmy_touch.Pressed(): Detects whether there is touch inputmy_touch.X()/my_touch.Y(): Gets touch coordinatesledcAttachChannel(): Binds a LEDC channel to a specified pinledcWrite(): Sets the PWM output value (0-255)
¶ Modification Instructions
If you need to modify the code display effect, you can refer to the following aspects for adjustment:
-
Modify Backlight Pin:
- Change
#define BACKLIGHT_PIN 21to another GPIO pin
- Change
-
Modify PWM Parameters:
- Adjust the values of
freq(frequency),channel(channel), andresolution(resolution) variables
- Adjust the values of
-
Modify Initial Brightness:
- Change the initial brightness value in
ledcWrite(BACKLIGHT_PIN, 255)
- Change the initial brightness value in
-
Modify UI Colors:
- Modify the slider track color (0x07FF), slider thumb color (TFT_MAGENTA), etc.
-
Modify Slider Position and Dimensions:
- Adjust the coordinate parameters of
fillRoundRect()andfillCircle()
- Adjust the coordinate parameters of
-
Modify Touch Calibration Parameters:
- Adjust the calibration values in
setCal()according to the actual touch screen characteristics
- Adjust the calibration values in
-
Modify Screen Rotation Direction:
- Change the parameter of
setRotation()(0-3) to alter the screen display direction
- Change the parameter of