TFT_eSPI and round display (GC9A01)

[STM32ardui]

As preparation for something like a GPS sport logger I tested a round TFT-display. Diameter is 1.28 inch and resolution 240 x 240 pixel, controller GC9A01. I want to know, which font size I need for good readability.

Is it ok, to show my sketch here?

TFT_eSPI library knows this display-controller, so it is easy to write a small sketch. For my test I use a STM32F411CEUS "BlackPill"-board.

Inside variant_BLACKPILL_F411CE.h:

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 PA4    CS
 PA7    MOSI      (on display SDA)
 PA6    MISO
 PA5    CLK       (on display SCL) 

So I use these pins. Of course a display don't send data to µC and MISO needs not to be connected.

If you use TFT_eSPI library, settings are not made inside your sketch. You have to look for a file User_setup.h inside library folder. At first view content of this file looks confusing and like a bunch of comments, because library can work with SPI and 8bit parallel and different microcontrollers. So you have to comment out, what you don't need and remove comment characters for what you need.

For my Blackpill-board this is a reduced User_Setup.h:

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// User defined information reported by "Read_User_Setup" test & diagnostics example
#define USER_SETUP_INFO "User_Setup"

// Define STM32 to invoke optimised processor support (only for STM32)
#define STM32
#define TFT_DC    PA12  // Data Command control pin
#define TFT_RST   PA8

// Only define one driver, the other ones must be commented out
#define GC9A01_DRIVER

// For ST7789, ST7735, ILI9163 and GC9A01 ONLY, define the pixel width 
// and height in portrait orientation
#define TFT_WIDTH  240 
#define TFT_HEIGHT 240 

// ######       EDIT THE PINs BELOW TO SUIT YOUR STM32 SPI TFT SETUP        ######

// The TFT can be connected to SPI port 1 or 2
//#define TFT_SPI_PORT 1 // SPI port 1 maximum clock rate is 55MHz
//#define TFT_MOSI PA7
//#define TFT_MISO PA6
//#define TFT_SCLK PA5

//#define TFT_SPI_PORT 2 // SPI port 2 maximum clock rate is 27MHz
//#define TFT_MOSI PB15
//#define TFT_MISO PB14
//#define TFT_SCLK PB13

// Can use Ardiuno pin references, arbitrary allocation, TFT_eSPI controls chip select
//#define TFT_CS   D5 // Chip select control pin to TFT CS
//#define TFT_DC   D6 // Data Command control pin to TFT DC (may be labelled RS = Register Select)
//#define TFT_RST  D7 // Reset pin to TFT RST (or RESET)
// OR alternatively, we can use STM32 port reference names PXnn
//#define TFT_CS   PE11 // Nucleo-F767ZI equivalent of D5
//#define TFT_DC   PE9  // Nucleo-F767ZI equivalent of D6
//#define TFT_RST  PF13 // Nucleo-F767ZI equivalent of D7



// Comment out the #defines below with // to stop that font being loaded
// The ESP8366 and ESP32 have plenty of memory so commenting out fonts is not
// normally necessary. If all fonts are loaded the extra FLASH space required is
// about 17Kbytes. To save FLASH space only enable the fonts you need!

#define LOAD_GLCD   // Font 1. Original Adafruit 8 pixel font needs ~1820 bytes in FLASH
#define LOAD_FONT2  // Font 2. Small 16 pixel high font, needs ~3534 bytes in FLASH, 96 characters
#define LOAD_FONT4  // Font 4. Medium 26 pixel high font, needs ~5848 bytes in FLASH, 96 characters
#define LOAD_FONT6  // Font 6. Large 48 pixel font, needs ~2666 bytes in FLASH, only characters 1234567890:-.apm
#define LOAD_FONT7  // Font 7. 7 segment 48 pixel font, needs ~2438 bytes in FLASH, only characters 1234567890:-.
#define LOAD_FONT8  // Font 8. Large 75 pixel font needs ~3256 bytes in FLASH, only characters 1234567890:-.
//#define LOAD_FONT8N // Font 8. Alternative to Font 8 above, slightly narrower, so 3 digits fit a 160 pixel TFT
#define LOAD_GFXFF  // FreeFonts. Include access to the 48 Adafruit_GFX free fonts FF1 to FF48 and custom fonts

// Comment out the #define below to stop the SPIFFS filing system and smooth font code being loaded
// this will save ~20kbytes of FLASH
#define SMOOTH_FONT


// For the STM32 processor define the SPI port channel used (default 1 if undefined)
//#define TFT_SPI_PORT 2 // Set to 1 for SPI port 1, or 2 for SPI port 2

// Define the SPI clock frequency, this affects the graphics rendering speed. Too
// fast and the TFT driver will not keep up and display corruption appears.
#define SPI_FREQUENCY  27000000

// Optional reduced SPI frequency for reading TFT
#define SPI_READ_FREQUENCY  20000000

// The XPT2046 requires a lower SPI clock rate of 2.5MHz so we define that here:
#define SPI_TOUCH_FREQUENCY  2500000

I overlooked a part made for STM32 and SPI. So I relied on library will know pins for SPI1 (CS, CLK, MOSI) and only defined TFT_DC and TFT_RST. But it works.

And information about font sizes may be wrong. I use FONT4 and FONT6. Inside TFT_eSPI.h I found:

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#ifdef LOAD_FONT4
  #include <Fonts/Font32rle.h>
  #define LOAD_RLE
#endif

#ifdef LOAD_FONT6
  #include <Fonts/Font64rle.h>
  #ifndef LOAD_RLE
    #define LOAD_RLE
  #endif
#endif

So you can also see, where standard fonts are stored.

Sketch is really small but uses 41708 bytes of program storage space and global variables 1696 bytes.

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#include <SPI.h>
#include <TFT_eSPI.h>       // TFT_eSPI@2.5.43

TFT_eSPI tft = TFT_eSPI();

void setup() {
  tft.init();
  tft.fillScreen(TFT_WHITE);
  tft.setCursor(48, 40, 6);
  tft.setTextColor(TFT_BLACK, TFT_WHITE);
  tft.print("3.25");
  tft.setTextFont(4);
  tft.print(" km");
  tft.setCursor(20, 95, 6);
  tft.print("0:12:30");
  tft.setTextFont(4);
  tft.print(" h");
  tft.setCursor(45, 150, 6);
  tft.print("10.5");
  tft.setTextFont(4);
  tft.print(" km/h");
}

void loop() {
  // put your main code here, to run repeatedly:
}

Result in the attached file.
I replaced first version with moire pattern with a better one.