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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 Raspberry Pi C++ 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: bcm2835 Library
  • 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 SPEED , SPI_CE_PIN

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 SPEED , SPI_CE_PIN

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

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

SPI_Speed (HW SPI Only)

Here the user can pass the SPI Bus freq in Hertz, Maximum 125 Mhz , Minimum 30Khz, The default in file is 8Mhz Although it is possible to select high speeds for the SPI interface, up to 125MHz, Don't expect any speed faster than 32MHz to work reliably. If you set to 0 .Speed is set to bcm2835 constant BCM2835_SPI_CLOCK_DIVIDER_32. If using SW spi, ignore.

SPI_CE_PIN (HW SPI Only)

Which Chip enable pin to use two choices. If using SW spi, ignore. * SPICE0 = 0 * SPICE1 = 1

SPI_CommDelay (SW SPI Only)

The user can adjust If user is having reliability issues with SW SPI in some setups. This is a microsecond delay in SW SPI GPIO loop. It is set to 0 by default, Increasing it will slow down SW SPI further.

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 Text_Graphic_Functions Tests text,graphics & function testing
3 Bitmap_Tests bitmap
4 Frame_rate_test_bmp Frame rate per second (FPS) bitmaps
5 Frame_rate_test_two Frame rate per second (FPS) text + graphics

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 GPIO5
3 SDA SPI_MOSI GPIO6
4 A0/DC GPIO24 GPIO24
5 RESET GPI025 GPIO25
6 SS/CS SPI_CE0 GPIO8
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

Multiple SPI devices

When using hardware SPI for multiple devices on the bus. If the devices require different SPI settings (speed of bus, bit order , chip enable pins , SPI data mode). The user must call function TFTSPIHWSettings() before each block of SPI transactions for display in order to refresh the SPI hardware settings for that device. See github issue #1.