Configure Landzo 7″ Display for Raspberry Pi

I’ve started building a photobooth using one of the first generation Raspberry Pi I found in a drawer. More details are to come. Meanwhile, here are some notes to configure the Landzo 7″ touchscreen display.

The display is sold as compatible with Raspberry Pi and probably it is but it didn’t work out of the box. The box comes with a CD-ROM but I don’t have any way to read that old stuff anymore. The landzo.com website doesn’t seem to host the content of that CD-ROM either.

The Pi doesn’t use the correct video modes for the display out of the box so I had to read the documentation. The gist of it is that you need to add a new custom mode to /boot/config.txt as below:

# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=1
hdmi_mode=87
hdmi_cvt=800 480 60 3 0 0 0

If you’re interested, here is how I got to those numbers. I rebooted the Pi in VGA mode (hdmi_group=1 & hdmi_mode=1) and then ran the tools to interrogate the display:

pi@raspberrypi:~ $ /opt/vc/bin/tvservice -d edid.dat
Written 128 bytes to edid.dat

Parsed the file with the edidparser:

pi@raspberrypi:~ $ /opt/vc/bin/edidparser edid.dat 
Enabling fuzzy format match...
Parsing edid.dat...
HDMI:EDID version 1.3, 0 extensions, screen size 15x10 cm
HDMI:EDID features - videodef 0x80 !standby !suspend !active off; colour encoding:RGB444|YCbCr422; sRGB is not default colourspace; preferred format is native; does not support GTF
HDMI:EDID ignored unknown descriptor tag 0x10
HDMI:EDID ignored unknown descriptor tag 0x10
HDMI:EDID ignored unknown descriptor tag 0x10
HDMI:EDID does not yet know monitor vertical range, setting to default 24 to 120Hz
HDMI:EDID failed to find a matching detail format for 800x480p hfp:40 hs:48 hbp:40 vfp:13 vs:3 vbp:29 pixel clock:32 MHz
HDMI:EDID calculated refresh rate is 66 Hz
HDMI:EDID guessing the format to be 800x480p @70 Hz
HDMI:EDID found unknown detail timing format: 800x480p hfp:40 hs:48 hbp:40 vfp:13 vs:3 vbp:29 pixel clock:32 MHz
HDMI:EDID established timing I/II bytes are 00 00 00
HDMI:EDID standard timings block x 8: 0x0101 0101 0101 0101 0101 0101 0101 0101 
HDMI:EDID adding mandatory support for DMT (4) 640x480p @ 60Hz
HDMI:EDID filtering formats with pixel clock > 162 MHz or h. blanking > 1023
HDMI:EDID no known preferred format has been set
HDMI:EDID filtering preferred group has been changed from Invalid to DMT
HDMI:EDID best score mode initialised to DMT (4) 640x480p @ 60 Hz with pixel clock 25 MHz (score 0)
HDMI:EDID best score mode is now DMT (4) 640x480p @ 60 Hz with pixel clock 25 MHz (score 36864)
HDMI:EDID preferred mode is updated to DMT (4) 640x480p @ 60 Hz with pixel clock 25200000 Hz
HDMI:EDID has only DVI support and no audio support
edid_parser exited with code 0

From there I saw this interesting line:

HDMI:EDID guessing the format to be 800x480p @70 Hz

I know the display’s resolution is 800×480 so that has to be my clue for the new mode. The docs gave me the rest.

hdmi_cvt=<width> <height> <framerate> <aspect> <margins> <interlace> <rb>

Value Default Description
width (required) width in pixels
height (required) height in pixels
framerate (required) framerate in Hz
aspect 3 aspect ratio 1=4:3, 2=14:9, 3=16:9, 4=5:4, 5=16:10, 6=15:9
margins 0 0=margins disabled, 1=margins enabled
interlace 0 0=progressive, 1=interlaced
rb 0 0=normal, 1=reduced blanking

The next challenge is to enable the touchscreen: the driver is probably in the CD-ROM and I haven’t found it online yet.

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