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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.

1.8" 160x128 pixel TFT-LCD

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

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.

Stripboard Layout

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:

Built stripboard

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

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