Resistive Touchscreen Manual Install & Calibrate

If you've grabbed our Easy Install image, or used the installer script, this step is not required, it's already done! This is just for advanced users who are curious on how to configure and customize the touchscreen
This procedure is identical for the 2.4", 2.8", 3.2" and 3.5" Resistive PiTFTs. Not for use with the Capacitive PiTFT!

Setting up the Touchscreen

Now that the screen is working nicely, we'll take care of the touchscreen. There's just a bit of calibration to do, but it isn't hard at all.

Before we start, we'll make a udev rule for the touchscreen. That's because the eventX name of the device will change a lot and its annoying to figure out what its called depending on whether you have a keyboard or other mouse installed.


sudo nano /etc/udev/rules.d/95-stmpe.rules

to create a new udev file and copy & paste the following line in:

SUBSYSTEM=="input", ATTRS{name}=="stmpe-ts", ENV{DEVNAME}=="*event*", SYMLINK+="input/touchscreen" 

Remove and re-install the touchscreen with

sudo rmmod stmpe_ts; sudo modprobe stmpe_ts

Then type ls -l /dev/input/touchscreen
It should point to eventX where X is some number, that number will be different on different setups since other keyboards/mice/USB devices will take up an event slot

There are some tools we can use to calibrate & debug the touchscreen. Install the "event test" and "touchscreen library" packages with

sudo apt-get install evtest tslib libts-bin

Running evtest

Now you can use some tools such as

sudo evtest /dev/input/touchscreen

which will let you see touchscreen events in real time, press on the touchscreen to see the reports.

AutoMagic Calibration Script

If you rotate the display you need to recalibrate the touchscreen to work with the new screen orientation. You can manually run the calibration processes in the next section, or you can run a small Python script which will automatically set a default touchscreen calibration based on the screen orientation.

This helper is automatically installed for you but if you'd like you can check it out here on github

Run it at the command line with

sudo adafruit-pitft-touch-cal

it will try to figure out what display you have installed and the rotation it's set up for

By default the script will attempt to read the screen orientation by examining the PiTFT module configuration with modprobe. If the script can read the orientation it will print out the current orientation, the current touchscreen calibration values, and the new touchscreen calibration values baesd on the current orientation. Before updating the calibration the script will ask you to confirm that you'd like to make the change. Press y and enter to confirm.

Try using this default calibration script to easily calibrate your touchscreen display. Note that the calibration values might not be exactly right for your display, but they should be close enough for most needs. If you need the most accurate touchscreen calibration, follow the steps in the next section to manually calibrate the touchscreen.

Manual Calibration

If the "automagic" calibration technique isn't working for you, or you have some other setup where you need to carefully calibrate you can do it 'manually'

You will want to calibrate the screen once but shouldn't have to do it more than that. We'll begin by calibrating on the command line by running

sudo TSLIB_FBDEVICE=/dev/fb1 TSLIB_TSDEVICE=/dev/input/touchscreen ts_calibrate

follow the directions on the screen, touching each point. Using a stylus is suggested so you get a precise touch. Don't use something metal, plastic only!

You should see five crosshair targets. If you see less than that, the touchscreen probably generated multiple signals for a single touch, and you should try calibrating again.

Next you can run

sudo TSLIB_FBDEVICE=/dev/fb1 TSLIB_TSDEVICE=/dev/input/touchscreen ts_test

which will let you draw-test the touch screen. Go back and re-calibrate if you feel the screen isn't precise enough!

X Calibration

You can also calibrate the X input system but you have to use a different program called xinput_calibrator

You can do this if the calibration on the screen isnt to your liking or any time you change the rotate=XX module settings for the screen. Since the screen and touch driver are completely separated, the touchscreen doesn't auto-rotate

Normally you'd have to compile it but we have a ready to go package for you so run:

sudo apt-get install -y xinput-calibrator

Before you start the xinput_calibrator you will need to delete the old calibration data so run

sudo rm /etc/X11/xorg.conf.d/99-calibration.conf

Before running startx and the calibrator - otherwise it gets really confused!

Now you'll have to run the xcalibrator while also running X. You can do this by startx and then opening up the terminal program and running the xinput_calibrator command (which is challenging to do on such a small screen) OR you can do what we do which is run startx in a SSH/Terminal shell and then run the xinput_calibrator from the same shell, which requires the following command order:

FRAMEBUFFER=/dev/fb1 startx &
DISPLAY=:0.0 xinput_calibrator

Follow the directions on screen

Once complete you'll get something like:
Run sudo nano /etc/X11/xorg.conf.d/99-calibration.conf and copy the
Section "InputClass"
        Identifier      "calibration"
        MatchProduct    "stmpe-ts"
        Option  "Calibration"   "172 3763 3769 164"
        Option  "SwapAxes"      "1"

or whatever you got, into there. You can quit X if you want by typing fg to bring that command into the foreground, and then Control-C to quit.

Depending on the 'rotation' of the screen, when you do this calibration, you may need to comment out the SwapAxes part with a # and/or swap the numbers around so looks like:

Option "Calibration" "119 3736 3850 174"


Option "Calibration" "3736 119 174 3850"

Your touchscreen is now super calibrated, hurrah!

Last updated on 2016-10-18 at 07.47.29 PM Published on 2013-11-29 at 02.19.02 PM