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So I'm trying to get a touchscreen from Chalkboard Electronics to work with my model B Raspberry Pi. The specific product I have is this 7" capacitive touchscreen which connects to the Raspberry Pi over HDMI using an HDMI-LVDS converter.

I'm using Raspbian wheezy 2012-10-28 as my operating system and the EDID file supplied by the manufacturer. My config.txt file contains:

hdmi_edid_file=1
hdmi_group=2
hdmi_mode=28
framebuffer_width=1024
framebuffer_height=600
hdmi_ignore_cec=1
hdmi_force_hotplug=1
config_hdmi_boost=4

However, I get no output on the screen. The backlight of the display lights up, Raspberry Pi's red light is on steady, green light flashes (in no particular sequence). I've also connected the Pi to a standard HDMI monitor (after disabling option for EDID) and it works fine. I've separately plugged in the touchscreen via the HDMI-LVDS converter into a Windows laptop, and the touchscreen does display output. I've also used the SD card test image used by the manufacturer - and no dice.

Are there any solutions for the display not working, or diagnostic steps I can carry out?

  • I don't know if the file behind your link "EDID file supplied by the manufacturer." (to goo.gl/Cehkw) is even for the correct device, but the file I could download from there is not even a valid EDID file. Both edid-decode and parse-edid report that the file has incorrect checksum. It appears to describe a mode for dimensions 154x81mm in a 170x100mm chassis. Is image not even full-frame? – Stéphane Gourichon Dec 22 '19 at 8:40
  • Also, did the manufacturer themselves provide that shortened URL goo.gl/Cehkw which actually link to a binary file downloadable from docs.google.com? If yes, then distributing an opaque binary file without even a meaningful file name, README file or any way to check if that file is correct for your hardware is piling up bad practice. – Stéphane Gourichon Dec 22 '19 at 8:48
  • Even assuming for a second that there might be some quality work initially, no wonder users struggle to find a working configuration. Did the manufacturer provide a web page with a permanent URL explaining step by step, offering downloads URLs to meaningful filenames with instructions to confirm to which hardware it applies? Or perhaps an archive file with all necessary information, configuration and files in a single package clearly stating for which hardware it is intended. Else writing "you wrote complete mess of settings" may be at least partly their fault. – Stéphane Gourichon Dec 22 '19 at 8:50
2

I solved this problem by adding this line to my config.txt file:

hdmi_ignore_edid=0xa5000080

Turns out that the touchscreen, to use the words used by Raspberry Pi wiki, is a "crappy Chinese" one and needs this line to work correctly.

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2

Your original settings are wrong, you don't need to change config.txt file because our LCD has EDID and RasPi can detect correct resolution itself. You wrote complete mess of settings in config.txt, so no wonder that LCD didn't work correctly.

hdmi_ignore_edid line is also not required. You can make simple test by connecting our LCD to normal PC and you will see that correct resolution will be automatically detected.

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  • Thank you for providing another answer. How do you explain that "the SD card test image used by the manufacturer" did not work, then? That should have worked, right? – Stéphane Gourichon Dec 22 '19 at 8:25

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