Adding touch support for the MI0283QT* displays

In my last posts I showed how to integrate Watterott’s MI0283QT-2 and the newer -9 displays as a frame buffer device in Raspberry Pi’s Linux kernel. Now I will focus on adding support for the touch controller found on the display boards.

The touch controller is an ADS7846 chip that already has a device driver in the Linux kernel. User dronus has patched the vanilla driver to make it work with the MI0283QT displays and the Raspberry Pi.

Fine, we already have everything in place now to give it a try!


First, we need to add two additional wires in our hardware setup to connect the touch controller (see old wiring in last post) with the RPi:

Signal     Raspi      Display   Comment
T_IRQ      GPIO25       13       Interrupt line from ADS7846
T_CS       SPI0_CE0_N   11       SPI chip select 0


I assume you already have a patched Linux kernel with the tft driver patches applied. Here is quick list with the next steps:

  • (Manually) apply dronus small patch to your kernel tree. This adds the necessary modifications of the ADS driver.
  • Note: I had to replace the invert_x with the invert_y entry in the ADS configuration to match the display orientation we use in the frame buffer driver
  • Your SPI config for the display now should look like this (for the newer *-9 display): linux/file arch/arm/mach-bcm2708/bcm2708.c
static struct ads7846_platform_data ads7846_config = {
  .x_max      = 0x0fff,
  .y_max      = 0x0fff,
  .x_plate_ohms    = 180,
  .pressure_max    = 255,
  .debounce_max    = 10,
  .debounce_tol    = 3,
  .debounce_rep    = 1,
  .gpio_pendown    = 25,
  .keep_vref_on    = 1,
  .swap_xy     = true,
  .invert_y    = true

static struct spi_board_info bcm2708_spi_devices[] = {
                // ads7846 touchscreen on chipsel=0 device
                .modalias    = "ads7846",
                .bus_num    = 0,
                .chip_select    = 0,
                .max_speed_hz           = 500000,
                .irq      = GPIO_IRQ_START+25,
                .platform_data    = &ads7846_config,
                .mode = SPI_MODE_0
        }, {
                // display on chipsel=1 device
                .modalias = "ili9341fb",
                .max_speed_hz = 16000000,
                .bus_num = 0,
                .chip_select = 1,
                .mode = SPI_MODE_0,
                .platform_data = &(struct fbtft_platform_data) {
                        .gpios = (const struct fbtft_gpio []) {
                                { "reset", 23 },
                                { "led", 24 },
                        .fps = 10
  • I use GPIO 25 for the touch IRQ (mainly because wiring was easier this way 🙂 and had to change the relevant entries. dronus used GPIO 17 instead.
  • I reduced the SPI rate of the display to 16 MHz and the frame rate to 10 fps. This proved to be more stable with activated touch controller.
  • The older -2 display works similarly. You only have to exchange the second block with the one of the r61505u driver. See old post for details
  • Open the configuration of the kernel and select the ADS driver:
> make menuconfig
Select "Device Drivers -> Input Device Support -> [*] Touchscreens -> [*] ADS7846..."
  • Make sure to include the ADS driver directly into the kernel and NOT in a module
  • Ok, thats it! (Re-)compile kernel and install it on your RPi…


After a reboot your system shows a new input device in /dev/input/*. If no other USB mouse or keyboard is connected then the devices found there are all created by the touch controller.

You can use the evtest utility to check the touch operation (Install with ‘apt-get install evtest’ first!):

> evtest /dev/input/event0

When you tap on the display you will see the incoming events. Note the x and y coordinates mapping if you tap on different corners of the display.

Now with the basic operation tested you can start X11 on your display (see last post) and use your fingers or a stylus to navigate the mouse cursor!

Open Topic

While touch operation with this driver is rock solid and works very precisely I have found one little nuisance: I can’t move the X11 cursor into the border regions of the display 🙁 Approx 5 mm at the border of the visibile display area my touch movements are not recognized anymore and I can’t move the pointer there… I am not sure if this is a limitation of the display, of the ADS driver or the parameter set for the driver… If you find a workaround for this then please post a comment!

[Update: 21.4.2013] Pre-compiled Kernel

A pre-compiled Raspbian Wheezy Kernel 3.6.11+ with both ili9341 display and ads7846 touch driver (i.e. supporting all devices on the MI0283QT-9 board) is available for download here:

pifon: an audio baby monitor for two Raspberry Pis

Becoming a dad does not only completely change your life but also changes the scope of your hobby projects (If time still permits :)) My first self-made project made especially for my newborn baby boy Felix is called pifon and is an audio baby monitor realized with two Raspberry Pi devices.

the pifon project: two Raspberry Pis converted into an audio baby monitor


The hardware setup is fairly simple: one Pi, the pifon server, has a USB web cam attached. I use its internal microphone to record the voice of my little boy. The other Pi is the pifon monitor and has a set of analog speakers attached for the output. Additionaly, the mon device has an Adafruit RGB LCD Plate attached and I use the LCD on this little plate as output device and its 5 keys as user input. I did not mount the plate directly on the Pi but used a ribbon cable to detach it: This allows me to package the plate in its own housing (As it is easier to find a case for the plate alone):

pifon/mon: the listening Pi with the control panel attached

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Watterott MI0283QT-9A Display for the Rasbperry Pi

In my last post I attached the Watterott Display to my Raspi. The model MI0283QT-2 I have here is not available anymore and was replaced with the newer MI0283QT-9A display modul. Unfortunately, this new display uses a different graphics chip and thus the driver I wrote won’t work for these panels… 🙁

With my new display driver skills, I thought about adding this new module, too 🙂 A few days ago I received this new model and on the weekend I finally found a little time to investigate the new driver code… The new chip is an ILI9341 and uses a 9 bit SPI protocol to receive its commands… Phew, sounds a bit strange but notro’s fbtft driver framework again comes to the rescue: he has already supported the Adafruit22 which also uses 9 bit transfers and he also added an 9-bit SPI patch for the Raspi Linux kernel… With this starting point I was able to support the new display in a few hours:

Watterott's new MI0283QT-9A display running the boot console

Since the display supports the Linux framebuffer interface its also possible to run X11 with Xorg’s framebuffer driver on it:

The display also runs the X11 desktop

Again I was able to drive the display with a 32 MHz SPI clock (even 48 MHz works) and got a stable and smooth 25 fps for the 320×240 pixels in 16 Bit RGB.

If you want to setup this display on your own Raspi then read on…

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Watterott Display on Raspberry Pi

I really like my Raspberry Pi, but what I am missing is a tiny display matching the size of the board that can be used as primary display, the boot console or some graphics later on.

A very nice and cheap TFT display is the MI0283QT-Adapter (note: I got the -2 version not the newer -9 version that has another display driver chip!) sold by Watterott. Its mainly focused to be an add on for the Arduinos, but it should work on every embedded system providing SPI access.

For the Linux running on the Raspberry Pi a framebuffer driver for the display would be the best solution, as it allows you to use it as a boot console and then you can run everything that runs on a framebuffer device (e.g. X11, SDL, mplayer, …).

First I thought about writing a fresh driver from scratch but some google-fu showed me that there already exists a nice solution: user notro has written fbtft, a driver framework that allows to simplify writing an own driver for those tiny TFTs.

For the R61505u display chip found on my display board, there was no driver available, but thanks to notro’s powerful framework and Watterott’s example code (Thanks to Markus for porting the code to the Raspi), I was able to derive a new driver for this chip in a few hours: See my cloned fbtft Git Hub repository for the source.

It works really nice: with 32 MHz SPI clock I can run 25 frames per second and even watch movies with smooth display:

Playing Big Bug Bunny with MPlayer's fbdev output

If you compile the driver directly in your kernel (i.e. no modules) then you can use the display directly as the boot console of your board:

Linux Boot Console running on display

If you want to build this setup yourself then read on…

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