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touch screen GUI, SPI slave mode

Discussion in 'Embedded Systems and Microcontrollers' started by fabgar, Oct 25, 2013.

  1. fabgar

    Thread Starter New Member

    Oct 25, 2013
    Hey everyone,

    I'm working on this project that I want to control using a touch screen GUI. But I could really use some help.

    I've been searching and reading datasheets/specs for ages now, looking at single board computers, microprocessor boards, smart displays, embedded GUI solutions,.. etc. But nothing I've found so far seems to do what I need. So therefore I want to appeal to the expertise of the users on this forum.

    The device I want to control has just one way of communicating; SPI (as the master).
    And I'm looking for a touch screen solution that has its own LCD controller, MCU/Soc, (flash) memory etc .. because no video information is to be sent thru the SPI bus, really only some control information. So the essential properties I'm looking for are the following:

    - GUI device has to be in SPI slave mode.
    Directly supported both in hardware and in software.(because I found some solutions, like an oLinuXino which seemed ideal, until I found it's Linux OS, doesn't support SPI directly, and only half duplex. And I need to compile my own custom kernel, which is beyond my skills)

    - being able to connect a 7" touch screen

    - preferably a single board computer or microcontroller board.
    Because of the many expansion possibilities. Down the line I need to connect some analog inputs. Either directly or thru an analog input board.

    - fast booting OS
    if the OS is Linux, Android, etc ... or based on.

    It would be great if someone could recommend me a good board. Or point me in the right direction because I'm stuck at the moment and I'm so excited to continue my little project that has got me back into electronics since years.

    thank you, any help will be much appreciated !
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Which 7" touch screen have you chosen, and how much experience do you have working with it? ie; have you already obtained and tested code to drive the 7" colour display and the touch screen driver etc?

    Or did you expect to find a 7" touchscreen that is controlled by SPI and will plug straight into a Linux system?
  3. fabgar

    Thread Starter New Member

    Oct 25, 2013
    I haven't chosen a screen yet. At the moment I'm only concerned about finding a board that supports SPI in slave mode. When I evaluate that I will look into what options it has for connecting screens. Most likely parallel/GPIO .

    Because it's not the screen that needs to be controlled via SPI, it's the board that will control the screen that has to communicate via SPI to this device I've already built. (Which can't be changed, it only has one SPI connection. That's why my quest ;) starts from here and not from a screen)

    I have contacted companies like 4D systems, Amulet Technologies, Olimex, and these seem ideal, except .. they don't support SPI slave mode.

    thanx for the reply RB
    Last edited: Oct 26, 2013
  4. MrChips


    Oct 2, 2009
  5. fabgar

    Thread Starter New Member

    Oct 25, 2013
    I've just been checking the SPI specs of this board and can operate in slave mode ! So far this is a great candidate ;) I'll be checking out the rest of the docs this afternoon. Looks promising.

    Thanks a lot MrChips, appreciate it !
  6. John P

    AAC Fanatic!

    Oct 14, 2008
    Would a Raspberry Pi with a suitable display do this?

    Or you could get a cheap tablet computer and program a microcontroller to be a USB-to-SPI bridge. But you'd need to be confident that you could program the tablet to do its part.
  7. fabgar

    Thread Starter New Member

    Oct 25, 2013
    Thanx John.

    From what I can understand, the Raspberry PI hardware does support SPI in master/slave mode, but the OS, being Linux (or based) doesn't support slave mode. As is the case with most boards that run Linux.
    Which I find really strange, since I'm sure lots of prototypes must have been built based on this type of board. I guess those people write their own SPI drivers.

    Or I should look for an embedded Linux distro with SPI fully implemented. Which will immediately make a lot of boards a lot more interesting for me.

    Not sure about the tablet though.
  8. fabgar

    Thread Starter New Member

    Oct 25, 2013
    Just heard back from Arm9board, and the OK210 board seems to be exactly what I need. SPI works in both master and slave mode, full duplex. And the driver is activated, no need to recompile.

    So, thanks again MrChips.