post

Experimenting with the Pi

An overview of the breadboard based experimenters boards and deplyment PCBs for the Pi.

post

Tiny LCD DSPI based screens

A recent test of the tiny LCD screens (2.8 to 3.5 inch) I have, to assess if they support a recent version of Raspbian.

TinyLCD 3.5 and Adafruit 2.8 survive!

 

Itead 2.8 TFT Add-on V2.0 Touch

A small display, again one of those LCD screens attached via SPI. slow refresh, OS support frozen in time.

Instructions that worked for me, April 2020. 

https://www.itead.cc/blog/raspberry-pi-b-2-8-tft-add-on-v2-0-touch-function-realizing


Download Raspbian-2015-02-16.img into SD card, then launch Raspberry Pi B 
Its old Wheezy Debian, unsupported and outdated, so make sure you change to the legacy update, the official repository moved on. But there is a legacy repository!

Replace this line in /etc/apt/sources.list
deb http://legacy.raspbian.org/raspbian/ wheezy main contrib non-free rpi

Now you can do the 

sudo apt-get update

Do the usual raspi_config, add SPI support

sudo nano  /etc/modprobe.d/raspi-blacklist.conf
Comment the mask of spi out
#blacklist spi-bcm2708

Connect Raspberry Pi B+ 2.8 TFT Add-on V2.0 to Raspberry Pi B+ correctly

sudo apt-get install xinput evtest tslib libts-bin

Download the fbtft driver, and you may need to run the following command three times:
sudo REPO_URI=https://github.com/notro/rpi-firmware rpi-update

Finally get the codes:
*** Running pre-install script
Work around rpi-update issue #106
*** Updating firmware
*** Updating kernel modules
*** depmod 3.12.21+
*** Updating VideoCore libraries
*** Using HardFP libraries
*** Updating SDK
*** Running ldconfig
*** Storing current firmware revision
*** Running post-install script
/lib/firmware
*** Deleting downloaded files
*** Syncing changes to disk
*** If no errors appeared, your firmware was successfully updated to b77683205688d3f6ae2b32a3c7
f4e63de1c06a5d
*** A reboot is needed to activate the new firmware

By now,you need to reboot your Raspberry Pi B+
sudo reboot

sudo touch /usr/share/X11/xorg.conf.d/99-fbdev.conf

Configure the file /usr/share/X11/xorg.conf.d/99-fbdev.conf

sudo nano /usr/share/X11/xorg.conf.d/99-fbdev.conf

Section "Device"
  Identifier "itdb28"
  Driver "fbdev"
  Option "fbdev" "/dev/fb1"
EndSection

sudo modprobe fbtft_device name=itdb28 gpios=reset:5,dc:6,wr:12,cs:13,db00:20,db01:21,db02:22,d
b03:23,db04:24,db05:25,db06:26,db07:27 rotate=90 fps=50

Add the following contents to file /boot/config.txt
dtoverlay=ads7846,cs=1,speed=2000000,penirq=17,swapxy=1,xmin=230,xmax=3850,ymin=190,ymax=3850,p
max=255,xohms=100
startx &
 (you may have to reboot)

Load the touch driver
1.Add the following contents to file /boot/config.txt

dtoverlay=ads7846,cs=1,speed=2000000,penirq=17,swapxy=1,xmin=230,xmax=3850,ymin=190,ymax=3850,pmax=255,xohms=100
2.Reboot Raspberry Pi B+

sudo reboot
3.Load TFT display driver

sudo modprobe fbtft_device name=itdb28 gpios=reset:5,dc:6,wr:12,cs:13,db00:20,db01:21,db02:22,db03:23,db04:24,db05:25,db06:26,db07:27 rotate=90 fps=50
4.start up X Server

startx &
Adjust the X&Y directions of this touch screen
DISPLAY=:0 xinput --set-prop 'ADS7846 Touchscreen' 'Evdev Axis Inversion' 0 1
Test
·Check the event’s number which is in accord with the touch screen.

	cat /proc/bus/input/devices

This event’s number here is event3, then you need to execute the following command to do the calibration and test touch screen according to the event’s number you’ve got. When do calibrating, you’d better use touch pen to click the cross’s center unless you want a rough calibration result.

·Touch screen calibration

sudo TSLIB_FBDEVICE=/dev/fb1 TSLIB_TSDEVICE=/dev/input/event3 ts_calibrate

Hyperpixel 3.5 Pimoroni

3.5 inch touch screen. Superseeded by Hyperpixel 4.0

Reasonable quality, touch is, though it i capacitive, not too easy to use. Resistive screens an be handled with pens, not this one.

With current Buster not a perfect pair.

Two experiments:

Raspberry Pi 2 B V1.2 success

1 imaged a SD with current Buster (feb 2020)
2 booted on a Pi 4 1 GB
3 did the usual raspi-config things and update/upgrade
4 checked out the system, works as expected
5 curl https://get.pimoroni.com/hyperpixel | bash
6. rebooted , installed Hyperpixel

Result is a working display, HDMI whosw rainbow screen, touch is wrong, cursor moves opposite directions, axes mixed up.
So not too bad, but touch not configured correctly.

Fixed with, in a console window, the command

$ hyperpixel-rotate normal

which changed the orientation of the screen to what is aleady was, and changed the touch matrix to a working touch.

So far so good.

Raspberry Pi 4 1 GB failure

To check out the Pi4, current Buster (feb 2020) and Hyperpixel 3.5 I did the following:

1 imaged a SD with current Buster (feb 2020)
2 booted on a Pi 4 1 GB
3 did the usual raspi-config things and update/upgrade
4 checked out the system, works as expected
5 curl https://get.pimoroni.com/hyperpixel | bash
6. rebooted , installed Hyperpixel

Result is not a working Hyperpixel display, but reverse image on HDMI, Hyperpixel dead.
Which is the same effect as booting from the working Raspberry Pi 2 SD.
Maybe the curl https://get.pimoroni.com/hyperpixel | bash gets the old hyperpixel install and not the Pi 4 version? Looks like it.

So back to

1 imaged a SD with current Buster (feb 2020)
2 booted on a Pi 4 1 GB
3 did the usual raspi-config things and update/upgrade
4 checked out the system, works as expected
5 downloaded the Hyperpixel Pi 4 git repository
6. rebooted , installed Hyperpixel with ./setup.h

Result is Hyperpixel noise banner, HDMI shows normal screen

So install fails with the curl or setup, and instructions clearly wrong.Issue opened at Pimoroni.

Adafruit PITFT 2.8 resistive


Image Raspbian full if you want a desktop, else lite is sufficient for CLI.

sudo apt-get update
sudo apt-get upgrade
sudo apt-get remove piwiz

sudo raspi-config
 - password
 - Boot to console autologon, no splash screen
 - localization time zone
 - Interfacing  - SSH SPI I2C Serial
 
wget https://raw.githubusercontent.com/adafruit/Raspberry-Pi-Installer-Scripts/master/adafruit-pitft.sh
chmod +x adafruit-pitft.sh
sudo ./adafruit-pitft.sh

Choose 1 tft 2.8 resistive
Choose 1 90 degrees
Console on tft Yes

reboot and console on tft visible

sudo sed -i "s+/dev/fb0+/dev/fb1+" /usr/share/X11/xorg.conf.d/99-fbturbo.conf
y       cat /usr/share/X11/xorg.conf.d/99-fbturbo.conf


sudo nano /usr/share/X11/xorg.conf.d/40-libinput.conf
At section touchscreen, add the following line
CODE: SELECT ALL
     Option "TransformationMatrix" "0 -1 1 1 0 0 0 0 1"

This matrix fits for the 90° turned display (see rotate=90 at /boot/config.txt). In case you have turned the display 270, the line must be
CODE: SELECT ALL
     Option "TransformationMatrix" "0 1 0 -1 0 1 0 0 1"

This design uses the hardware SPI pins (SCK, MOSI, MISO, CE0, CE1) as well as GPIO #25 and #24. All other GPIO are unused. Since we had a tiny bit of space, there's 4 spots for optional slim tactile switches wired to four GPIOs, that you can use if you want to make a basic user interface. For example, you can use one as a power on/off button.

We bring out GPIO #23, #22, #21, and #18 to the four switch locations!

The last known for-sure tested-and-working version is March 13, 2018 (https://downloads.raspberrypi.org/raspbian/images/raspbian-2018-03-14/) from https://downloads.raspberrypi.org/raspbian/images/

It works OK with recent Buster (Jan 2020), tested March 2020

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.

Check if this already done

   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" 

   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

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 re-run the installer script and select a new rotation:

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!

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 xtcal (xinput_calibrator no longer works)

You can do this if the calibration on the screen isn't 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

Download and compile it with the following:

 Download: fileCopy Code
sudo apt-get install libxaw7-dev libxxf86vm-dev libxaw7-dev libxft-dev
git clone https://github.com/KurtJacobson/xtcal
cd xtcal
make
You must be running PIXEL (the GUI) while calibrating.

Before you start the calibrator you will need to 'reset' the old calibration data so run

DISPLAY=:0.0 xinput set-prop "stmpe-ts" 'Coordinate Transformation Matrix' 1 0 0 0 1 0 0 0 1
Now you'll have to run the calibrator while also running X. You can do this by opening up the terminal program and running the the xtcal command (which is challenging to do on such a small screen) OR you can do what we do which is create an SSH/Terminal shell and then run the calibrator from the same shell, which requires the following command:

DISPLAY=:0.0 xtcal/xtcal -geometry 640x480
Note that the geometry may vary!

If you are using a 2.4"/2.8"/3.2" 320x240 display with landscape orientation, use 640x480. If you're in portrait, use 480x640.

If you are using a 3.5" display with landscape, use 720x480, portrait is 480x720

Follow the directions on screen

raspberry_pi_xinput.png
Once complete you'll get something like:
adafruit_products_testxtcal.png
Run sudo nano /usr/share/X11/xorg.conf.d/20-calibration.conf and copy the 9 numbers into the TransformationMatrix option so it looks like:

 Download: fileCopy Code
Section "InputClass"
        Identifier "STMPE Touchscreen Calibration"
        MatchProduct "stmpe"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
        Option "TransformationMatrix" "-0.000087 1.094214 -0.028826 -1.091711 -0.004364 1.057821 0 0 1"
EndSection
or whatever you got, into there.

You will want to reboot your Pi to verify you're do