AVRTFT

Experimental project to drive a TFT LCD with an AVR MCU (ATmega328P) and avr-libc.

Currently supported displays/drivers:

• Adafruit 1.8" Color TFT LCD 160x128 ST7735R
• Adafruit 2.0" Color IPS TFT 320x240 ST7789
• Adafruit 2.8" Color TFT LCD with Cap Touch 320x240 ILI9341

Additionally, there is some support for larger (up to 800x480) TTL displays, for example the
Adadruit 7.0" 40-pin TFT Display - 800x480 with Touchscreen,
with the RA8875 controller like the
RA8875 Driver Board for 40-pin TFT Touch Displays
including touch support.

Currently implemented features:

• Mostly complete UTF-8 set (code points U+0000 to U+00FF) of Hack font
  with antialiasing (4-Bit greyscale)
• Some emojis (16-Bit RGB)
• Write text in Hack including emojis 🙂
• Draw bitmaps
• Write text and bitmaps via USART
• Upload BMP images via USART (16-Bit 5/6/5 RGB)
• Basic SD card support: read and write blocks of 512 bytes
• Read BMP images from SD card (raw)
• Process touch events (FT6206, RA8875)
• Very basic paint application
• Logging via USART

Ideas:

• Make features usable from a touch screen menu

Write something via USART

Connect to the controller with for example GTKTerm (38400 Baud).
Write some text and a bitmap, and upload a BMP image:

c 0xffff // clear display
d // display the demo
t 0 0 Just some text // write text in Hack to row 0 column 0
b 0 0 1 // write bitmap with index 1 (tiny Linus cat) to row 0 column 0
p 0 0 // prepare to "stream" a 16-Bit (5/6/5) RGB BMP image to row 0 column 0
cat Bali160x128.bmp > /dev/ttyUSB0 // upload a BMP image
s 0 // read BMP image from SD card starting at address 0 (to row 0 column 0)
a // start paint application

Enter emojis

Emojis are entered with a tabulation char + their "code", i.e. Smile!<TAB>s for a smiling emoji.

Convert and write images to SD card

Without any file system, to write any number of pictures with a specific
resolution as 16-Bit (5/6/5) RGB BMP image files:

1. Convert pictures with ImageMagick 'convert' and pad them to a multiple of
   512 bytes

    for i in *.jpg; do convert $i -scale 320x240 -define bmp:subtype=RGB565 $i.bmp; truncate -s 154112 $i.bmp; echo $i; done

2. Concatenate the images to a single file

    for i in *.bmp; do cat $i >> sdcard.img; echo $i; done

3. Write the images raw to SD card (danger zone!)

    sudo dd if=sdcard.img of=/dev/mmcblk0 bs=512

Now the images can be read one by one from SD card with an address offset of 301.

Paint application

A super basic paint application created to learn about processing touch events
and draw something on the screen.

The FT6206 based touch screen of the
Adafruit 2.8" Color TFT LCD with Cap Touch 320x240 ILI9341
works quite well but at least for me the coordinates of touches close to the
long edges of the screen are a bit off (too close to the edge) and there seems
to be no calibration capability - the data sheet mentions "auto calibration".

But still it is fun and it should be possible to create an application
supporting touch with reliable usability.

Larger (up to 800x480) TTL displays

If at all possible, it probably is quite a challenge to drive such a 40-pin display with a 28-pin
MCU like the ATmega238P, but it is easy with the RA8875 driver, offering support for a touch screen
as well. Here it is combined with the SparkFun Level Shifting microSD Breakout
to read images from an SD card, advancing to the next image by touching the screen.