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ST7735 TFT Readme

Image TFT

Table of contents

Overview

  • Name: ST7735_TFT
  • Description:
  1. C++ Library for a TFT SPI LCD, ST7735 Driver
  2. Dynamic install-able Linux based Single Board ComputersC++ library.
  3. Inverse colour, rotate, sleep, idle & vertical scroll modes supported.
  4. Graphics + print class included.
  5. 24 bit colour , 16 bit color & bi-color Bitmaps supported.
  6. Hardware and Software SPI
  7. Dependency: lgpio Library
  8. NB 'spidev.bufsiz' setting must be 65536 or greater see Notes section.
  • Author: Gavin Lyons
  • Port of my PIC library at github link.

Software

User options

In the example files. There are 3 sections in "Setup()" function where user can make adjustments to select for SPI type used, PCB type used and screen size.

  1. USER OPTION 1 GPIO/SPI TYPE
  2. USER OPTION 2 SCREEN SECTION
  3. USER OPTION 3 PCB_TYPE, + SPI SETTINGS

USER OPTION 1 SPI TYPE / GPIO

This library supports both Hardware SPI and software SPI. The TFTSetupGPIO function is overloaded(2 off one for HW SPI the other for SW SPI). The parameters set for TFTSetupGPIO define which is used. HW SPI is far faster and more reliable than SW SPI

USER OPTION 2 Screen size + Offsets

User can adjust screen pixel height, screen pixel width and x & y screen offsets. These offsets can be used in the event of screen damage or manufacturing errors around edge such as cropped data or defective pixels. The function TFTInitScreenSize sets them.

USER OPTION 3 PCB Version, SPI Settings

TFTInitPCBType function is overloaded(2 off, one for HW SPI the other for SW SPI).

parameter default value note SPi type
SWSPI_CommDelay 0 uS delay for GPIO to change speed software
HWSPI_DEVICE 0 A SPI device, >= 0. which SPI interface to use , ls /dev/spi* Hardware
HWSPI_CHANNEL 0 A SPI channel, >= 0. Which Chip enable pin to use usually 0 or 1 Hardware
HWSPI_SPEED 1000000 The speed of serial communication in bits per second. Hardware
HWSPI_FLAGS 0 mode 0 for this device Hardware
GPIO_CHIP_DEVICE 0 gpio chip device >= 0, check ls/dev/gpiochip* both
PCB_TYPE TFT_ST7735R_Red see table and text below Both

PCB_TYPE: In the main.cpp in USER OPTION 3 PCB_TYPE select your display type, by passing an enum type to function TFTInitPCBType. Default is "TFT_ST7735R_Red". There are 4 types of the ST7735 TFT display supported. If your display works but RGB colors are wrong you may have chosen wrong display type.

Number Description Enum label Tested
1 ST7735B controller TFT_ST7735B n/a
2 ST7735R Green Tab TFT_ST7735R_Green n/a
3 ST7735R Red Tab TFT_ST7735R_Red RED PCB v1.1, 1.44, 128x128 pixels
4 ST7735S Black Tab TFT_ST7735S_Black RED PCB v1.2, 1.8, 128 x 160 pixels

File system

In example folder: The Main.cpp file contains tests showing library functions. A bitmap data file contains data for bi-color bitmaps and icons tests. The color bitmaps used in testing are in bitmap folder, 3 16-bit and 5 24-bit images.

# example file name Desc
1 Hello_world Basic use case
2 Hello_world_SWSPI Basic use case fro software spi
3 Text_Graphic_Functions Tests text,graphics & function testing
4 Bitmap_Tests bitmap
5 Frame_rate_test_bmp Frame rate per second (FPS) bitmaps
6 Frame_rate_test_two Frame rate per second (FPS) text + graphics
7 Multiple_displays shows use of two displays on same spi bus(OLED AND LCD)

Bitmap

There are four class functions to support drawing bitmaps

Function Name Colour support Pixel size Note
drawIcon bi-colour (0-127) X 8 Data vertically addressed
drawBitmap bi-colour 2048 bytes max Data horizontally addressed
drawBitmap16 16 bit color 565 BMP files 32K max ------
drawBitmap24 24 bit color BMP files 48K max Converted by software to 16-bit color
  1. Bitmap size in kiloBytes = (screenWidth * screenHeight * bitsPerPixel)/(1024 * 8)
  2. Pixel size column assumes 128 by 128 screen.

These class functions will return an error code in event of error see API for more details.

Hardware

Connections as setup in main.cpp test file.

TFT PinNum Pindesc RPI HW SPI RPI SW SPI
1 LED VCC VCC
2 SCLK SPI_CLK GPIO6
3 SDA SPI_MOSI GPIO5
4 A0/DC GPIO24 GPIO24
5 RESET GPI025 GPIO25
6 SS/CS SPI_CE0 GPI21
7 GND GND GND
8 VCC VCC VCC
  1. Connect LED backlight pin 1 thru a 150R/220R ohm resistor to 3.3/5V VCC.
  2. This is a 3.3V logic device do NOT connect the I/O logic lines to 5V logic device.
  3. You can connect VCC to 5V if there is a 3.3 volt regulator on back of TFT module.
  4. Pick any GPIO you want for SW SPI for HW SPI: reset and DC lines are flexible.
  5. User can select SPI_CE0 or SPI_CE1 for HW SPI
  6. Backlight control is left to user.

Wiring pic

Output

  1. Clock Demo showing icons, small bitmaps
  2. 24-bit color bitmap test image
  3. 16-bit color bitmap test image

Demo pic

Notes

spidev buf size

The maximum transaction size that 'lgpio' can handle by default is 65536 bytes. So this is also the maximum transaction size of Display_lib_RPI, if more than that needs to be sent it is sent in blocks of 65536 bytes. Certain 'Display_lib_RPI' functions use buffered writes, the ones that draw bitmaps, write fonts, fill rectangles, clear screen, etc. In order for this to work the spidev.buf size must be at least 65536. To check the setting on your device run command:

cat /sys/module/spidev/parameters/bufsiz

If it is lower than 65536 you can change it by adding this to the start of line in file /boot/firmware/cmdline.txt.(raspberry pi ) Make sure everything is on one line and there is space ' ' between this parameter and next one. Then reboot machine. Verify again by running last cat command above

spidev.bufsiz=65536

bufsiz defines the number of bytes that the SPI driver will use as a buffer for data transfers.