7 Replies Latest reply on Jan 6, 2017 11:58 AM by mconners

    Dual Raspberry PI 7" Touch screen monitors from same PI

    shdwknt

      First off I DO NOT need touchscreen to work.  I need strictly 2 monitors running from 1 raspberry pi - sharing the same screen/image.

       

      I bought a non-element14/Adafruit 10" monitor and it has HDMI in.. not paying attention I bought the 7" touch screen and there is no HDMI in for the display - I was going to just use an hdmi splitter and feed both displays that way - but I cant do that since the adafruit 7" isnt HDMI in supported..

       

      any thoughts on how I can get 2 of the adafruit 7" touch screens to share the same display from 1 Pi?

       

      I am using the PI 3 - and want a MIRRORED monitor output.

       

      Any and all help is appreciated.

       

      Thank you.

        • Re: Dual Raspberry PI 7" Touch screen monitors from same PI
          mconners

          What is the interface to the 7" display? Is it the DSI ribbon cable?

           

          Mike

          • Re: Dual Raspberry PI 7" Touch screen monitors from same PI
            shabaz

            Hi Rick,

             

            There is discussion here concerning running two displays with different interfaces simultaneously:

            How to run HDMI and Official Raspberry Pi Display (DSI) simultaneously?

            Regarding the adafruit non-HDMI display, the circuit is here:

            https://learn.adafruit.com/assets/24414

            To have two of them simultaneously displaying the same content would likely require

            some hacking around (i.e. stick the displays in parallel but just one EEPROM, and possibly

            you may need a buffer circuit too). I think the chances of it all working are low unless you

            have access to an oscilloscope. Also you can't extend them indefinitely and so there could

            be some issues there too, all depends on what is needed precisely, and may involve experimentation

            that may or may not result in success.

            You could just run two Pi's, one per screen. You can share content to be displayed using software

            methods over the network. However again it depends on your end use-case. It isn't possible

            to design the best solution without knowing the end goal in detail.

            2 of 2 people found this helpful
              • Re: Dual Raspberry PI 7" Touch screen monitors from same PI
                shdwknt

                here is what I am thinking - I am trying to run mame but give 2 players - each their own screen.

                 

                it would be like a head to head setup competiors facing each other each has their own screen.

                 

                The problem I am having is finding an hdmi display that works proper format in mame.   So I purchased the adafruit display but its not HDMI Im not looking to spend a small fortune on displays trying to find a pair that work.

                 

                if I can somehow split the FPC cable from the pi to 2 displays and mirror the screen i would be set - or could find a hdmi display that is supported by any of the mame emulators I would be further set

                  • Re: Dual Raspberry PI 7" Touch screen monitors from same PI
                    shabaz

                    Unfortunately I can't think of a way to use two of these displays simultaneously with any off-the-shelf option. You could try to combine the flex cables as you say, but it involves building up a circuit board (not difficult but still needs design effort and being comfortable soldering on the connectors which are quite fine pitched - it can be done with a normal soldering iron) so there is a fair amount of work effort. And it still might not work, it may need a buffer circuit, and maybe even changes to the supply, I've not checked the schematic or display specs in detail. Also, the displays wouldn't work very far apart (not sure if that is an issue for your use-case or not).

                    Basically it is feasible but a fair amount of effort and depends on what tools you have access to.

                    You could experiment with software methods to replicate the display, but I don't know if latency then becomes a problem, although I suspect you might be ok since a lot of video games are low-res. If I was designing it, I'd either look to see what existing software is out there (e.g. VNC or alternatives) or directly look into the source code and investigate ways of sending the low-res stream either directly or after some simple compression. For example if the typical video resolution for games is 320x240 then even at 30fps, 8-bit video is feasible over the network connection without compression. This then needs software work. Perhaps the MAME community should have this on their feature roadmap, if it is something many people wish to do. I don't think it is a major amount of work for someone already familiar with the right technologies, but I could be wrong.

                     

                    EDIT:

                    Apparently MAME already has an option to write frames to disk in a .mng format which seems to be each frame as a PNG format. With a bit of code, the video could be streamed (e.g. just over tcp, even http) and have a simple client running on the other side or even a browser.

                    So it does need someone to make the necessary code changes in MAME (or write some plugin, I have no idea about MAME software arch) but it possibly wouldn't be a lot. It would be a cleaner solution because then it would work with any displays and any computer, not just the Pi and

                    Adafruit display.

                    1 of 1 people found this helpful
                      • Re: Dual Raspberry PI 7" Touch screen monitors from same PI
                        shdwknt

                        Thanks - its not a viable solution for me. I am going to have to experiment with more small hdmi screens and continue to attempt to find one that mame likes so that I can just use the HDMI splitter to begin with.  I dont understand why the adafruit design DIDNT incorporate the HDMI input - considering the PI has built in HDMI out..  personally seems like a design miss to me - whatever.

                         

                        Thanks guys