ST7735 FrameBuffer for Raspberry Pi

The ST7735 is a single-chip controller/driver for 262K-color, graphic type TFT-LCD, which can be picked up on eBay relatively cheaply with pin-outs on a break-out board.

Tested working with Rev B 512Mb Rasberry Pi (Raspbian "Wheezy" & latest kernel sources - 3.8.11+). A couple of video demos are available here:

• https://vimeo.com/59438789
• https://vimeo.com/59765667

Further technical details for the LCD screen can be found in the datasheet [PDF]. Other documentation can also be found in docs/tech-spec.

Building and installing the frame buffer driver

1. On the Raspberry Pi, enable SPI: edit /etc/modprobe.d/raspi-blacklist.conf to comment out blacklisting of spi_bcm2708.

2. Ensure that the latest firmware has been applied to the Raspberry Pi. Use the updater from https://github.com/Hexxeh/rpi-update to perform the update (use the BRANCH=next prefix). After rebooting, confirm the kernel version as follows (digits xx and yyy dont matter too much):

   $ uname -a
   Linux raspberrypi 3.8.xx+ #yyy PREEMPT ...
   

3. Ensure the gcc build tools are installed on a host PC (it is much quicker to cross-compile on an x86 linux machine than build the kernel on the RPi):

   $ sudo apt-get install make build-essential ncurses-dev git-core
   

4. Download the kernel sources with the ST7735 drivers:

   $ mkdir ~/RPi
   $ cd ~/RPi
   $ git clone https://github.com/rm-hull/raspberrypi-linux.git
   $ git checkout rpi-3.8.y+rmh-st7735fb
   

5. Download the cross-compiler tools:

   $ cd ~/RPi
   $ git clone git://github.com/raspberrypi/tools.git
   

6. Follow the instructions for building a cross-compiled kernel here. Note that when the guide refers to .config, this is provided as etc/config.gz in git.

   Let's assume that the tools are installed in ~/RPi/tools, and the kernel source is ~/RPi/raspberrypi-linux. Briefly the compile steps are:

   $ cd ~/RPi
   $ export CCPREFIX=~/RPi/tools/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin/arm-linux-gnueabi-
   $ export MODULES_TEMP=~/RPi/modules
   $ wget https://github.com/rm-hull/st7735fb/raw/master/etc/config.gz
   $ cd raspberrypi-linux
   $ make mrproper
   $ zcat config.gz > raspberrypi-linux/.config
   $ make ARCH=arm CROSS_COMPILE=${CCPREFIX} oldconfig
   $ make ARCH=arm CROSS_COMPILE=${CCPREFIX} -j 6
   $ make ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=${MODULES_TEMP} modules_install
   

Once compiled, scp the arch/arm/boot/zImage over the /boot/kernel.img on the Raspberry Pi (make a backup first). Next copy the ~/RPi/modules/lib/modules/3.8.11+ directory to /lib/modules/3.8.11+ on the device (again move the existing directory out of the way first).

On rebooting, you should get a second frame buffer at /dev/fb1, and the screen should present a nice gradient pattern.

Break-out board pin-outs

There appear to be a large number of break-out boards available for this device; this is the one I have, with an additional SD card slot:

TFT Pin	Name	Remarks	RPi Pin	RPi Function	Wire color
1	GND	Ground	6	GND	Black
2	VCC	Power	1	3V3	Red
3	NC
4	NC
5	NC
6	RESET	Set low to reset	18	GPIO 24	Blue*
7	A0	Data/command select (aka DC or 'register select')	16	GPIO 23	Grey*
8	SDA	SPI data	19	GPIO 10 (MOSI)	Orange
9	SCK	SPI clock	23	GPIO 11 (SPI CLK)	Brown
10	CS	SPI chip select - set low	24	GPIO 8 (SPI CS0)	Green
11	SD-SCK	SD serial clock
12	SD-MISO	SD master in, slave out
13	SD-MOSI	SD master out, slave in
14	SD-CS	SD chip select
15	LED+	Backlight control 3V3 - 3V7, already fitted with 10K resistor?	1	3V3	Red
16	LED-	Backlight ground	6	GND	Black

*-not shown on stripboard layout below - direct track connection.

Stripboard Layout

With 4 push-buttons, resistor values 10K.

Buttons (from left to right) are wired onto BCM pins as follows:

• GPIO 22
• GPIO 25
• GPIO 17
• GPIO 14 (TxD)

Also: Dallas Semiconductors DS18B20 digital thermometer, wired onto GPIO 4, with 4.7K pull-up resistor. See separate usage note here.

Testing

mplayer

scale is used because the movie is larger than most small displays. -3 means keep aspect ratio and calculate height.

$ sudo mplayer -nolirc -vo fbdev2:/dev/fb1 -vf scale=156:-3,rotate=2 examples/video/bird-is-the-word.mp4 

Image viewer

$ FRAMEBUFFER=/dev/fb1 fim examples/images/tux-small.png

Using the LCD as a console device

To use the display as a console, the kernel must be re-compiled with the BCM SPI & ST7735 drivers 'baked in' rather than as separate modules (the config settings above do this); add this to the end of the line in /boot/cmdline.txt

fbcon=map:10 fbcon=rotate:3 fbcon=font:MINI4x6

See fbcon doc for more info.

And the finished article:

Examples

The framebuffer is owned by root, so first:

$ sudo -s
$ export FRAMEBUFFER=/dev/fb1

To demo the maze generator:

$ python maze.py

Copper bar animation:

$ python copper_bar.py

Snake game (needs Wii Remote and bluetooth enabled):

$ python snake.py

TODO

• Extended documentation

• Improve build instructions

• Example code (SDL / Python)

References

• http://elinux.org/Rpi_Low-level_peripherals#General_Purpose_Input.2FOutput_.28GPIO.29

• http://www.sitronix.com.tw/sitronix/product.nsf/Doc/ST7735?OpenDocument

• http://learn.adafruit.com/1-8-tft-display

• http://www.raspberrypi.org/phpBB3/viewtopic.php?t=28696&p=262909

• http://elinux.org/images/1/19/Passing_Time_With_SPI_Framebuffer_Driver.pdf

• http://www.flickr.com/photos/ngreatorex/7672743302/

• https://github.com/notro/fbtft

• http://www.areinhardt.de/news/raspberry-pi-tft-display/

• http://www.whence.com/rpi/

• http://fritzing.org

• http://harizanov.com/product/1-8-tft-display-for-raspberry-pi/