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  • Multiple screens

    Just checking that my understanding of reading previous post and the documentation is up to the job. To connect more than one screen I need separate TX and RX for each, preferably separate RESET while the GND and VCC (5V positive) are shared (Though I'm wondering how much I can actually get through a single board.... may have to look at powering the screens directly instead of through the board, suggestions welcomed).

    What I'm missing is understanding how the code segment:

    Code:
    Serial.begin(200000); // Serial0 @ 200000 (200K) Baud
    display1.Begin(Serial); // Use Serial0 for talking to the Genie Library, and to the 4D Systems display #1
    
    Serial1.begin(200000); // Serial1 @ 200000 (200K) Baud
    display2.Begin(Serial1); // Use Serial1 for talking to the Genie Library, and to the 4D Systems display #2
    knows which of the displays is the one connected to RX0 and TX0 and which is connected to RX1 and TX1, and so on (Yes, I can see that one is for display1 and the other display2, but how do they get assigned to the relevant RX and TX pins?). Does it simply look at RX0 and TX0 first (if something is connected), then increment the number to get the next one in the sequence with each successive call? I can see why you'd need to specify the RESET pin in such a situation, I just need to get my head around what it's actually doing here, so I don't accidentally reset the wrong screen.

    Looking at the mega I'm assuming that 4 screens is the maximum this board can control at once? I'm going to keep looking to see what possibilities this has and how I'm going to do what I'm planning, but this looks like an interesting starting point.
    Last edited by Eewec; 13th June 2016, 09:37 PM.

  • #2
    Looking at everything in more detail today and I'm a little surprised that a 4 screen shield for the mega isn't around for the 4D screens, although I suppose if you're using the mega maybe it's assumed the person knows where to put the cables..... Still, would be nice to have somewhere to tie a common external power source and reset cable(s) specifically for the screens as I'm not sure 4 screens would appreciate only getting power from the Arduino. Working out where to get that power from in the installation I'm think of is also going to be interesting.

    EDIT: OK, so I've been thinking about this and looking around for ideas. If I'm running enough displays to look like a proper cock pit that's _a lot_ of screens. especially if I start using the uLCD-220RD-AR for gauges... then things start getting really silly in terms of numbers needed for this project. Biggest issue with it all is getting enough power to everything which a quick search of ebay turned up http://www.ebay.com/itm/1PCS-Board-M...AAAOxy1RZSY9yF which while useful during the initial design doesn't really help long term. The only other idea I had was to plug each individual Arduino Mega board into a powered USB hub, but that still leaves me with possibly underpowered displays with 4 on each board. Does anyone know of a shield that is just power distribution from a powered usb hub for the additional boards attached to an Arduino?
    Last edited by Eewec; 15th June 2016, 07:29 AM.

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    • #3
      Hello Eewec,

      Still, would be nice to have somewhere to tie a common external power source and reset cable(s) specifically for the screens as I'm not sure 4 screens would appreciate only getting power from the Arduino.
      Yes ideally the 4 displays should be powered separately from the Arduino host. Remember to check the typical current draw of the displays that you will be using.

      Hopefully other forum users will be able to answer your other questions.

      Best Regards,
      Doff

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      • #4
        Originally posted by Doff View Post
        Hello Eewec,



        Yes ideally the 4 displays should be powered separately from the Arduino host. Remember to check the typical current draw of the displays that you will be using.

        Hopefully other forum users will be able to answer your other questions.

        Best Regards,
        Right. So the datasheet on the 'uLCD - 220RD Display Module' says the Programming header wants on the +5V in betwen 4.0V to 5.5V, nominal 5.0V and 500mA minimum Required. It's the same with the 'uLCD-70DT Display Module'. But I'm going to say that seems to only be true while programming the unit.... the 'uLCD - 220RD Display Module' seems to indicate that normal running varies but 150mA is otherwise fine.... well.... if you find the correct version of the datasheet as there appears to be 2;

        http://www.4dsystems.com.au/productp...heet_R_1_2.pdf

        and

        http://www.4dsystems.com.au/productp...heet_R_1_0.pdf

        If I go to gen4 screens then the voltage range is the same and I couldn't find a programming spec for Amps but general usage seem to say about 815 to 825 mA depending on the version (looking at 7in screens, the smaller ones need less).

        OK, so hardware only draws what it needs but I couldn't find anything that said the screens wouldn't like me if I gave them a clean 5V 1A - 2A power supply each. The trouble is sourcing such a thing, and while I was out earlier I may have had one of those eureka moments.... I'm off to do more research to see if it might work before I say anything else.
        Last edited by Eewec; 15th June 2016, 09:20 PM.

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        • #5
          Woot! I was right. PC PSU's typically have 1x +12V output rail and several.... wait for it.... 5V and 3.3V supplies. No idea on the Amperage on those or much of anything else, but it's looking like there might actually be a way around this that doesn't require me to learn every single thing in existence just to get a finished simpit, which although an exaggeration, at times it really doesn't feel like one. Now.... which PSU would be most ideal.... arrrgggg there are millions of different ones to choose from *groan*. Well at least once I've worked this bit out, any more power is just a case of buying an extra one.

          EDIT: Hmmm they put out 24Amps per line... ok so amps are drawn by the electronics but is that going to cause issues with the displays?
          Last edited by Eewec; 15th June 2016, 10:12 PM.

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          • #6
            Now I just need to either build my own circuits to split those 24Amp 3.3V and 5V lines into nice easily accessible 3.3V and 5V 1-2 Amp plus GND connections or find something that someone else has already made...

            Comment


            • #7
              The voltage of the power supply needs to match, i.e. 5v.

              The amps of the power supply just needs to be equal to or greater than the required amount.

              Be careful with PC power supplies as the designer often ASSUMES they will be used to power a PC. Thus when they are connected to something that isn't drawing a certain amount of power off all the lines they can either stop working, or output the wrong voltages.
              Mark

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              • #8
                Thank you for the heads up.

                That's the sort of info that unless you know to ask, you might not even realise it needs thinking about. That said, I was already thinking of ways to make sure that the 3.3 and 5 Volt rails worked properly and fed the correct Voltage when the 12V rail wasn't being used.... now I have another thing to look for (does it even power the 5.5 and 3.3 Volt rails properly when the 12V isn't being used?)

                Hmmm I wonder if any of the PC power supplies out there actually spec the ability to be used for other purposes..... that would be helpful and at this point in my research I've long ago realised that helpful and thoughtful design is somewhat of a rarity. Glad to see that from what I've read and looked at thus far 4D Systems seem to be one of the few companies out there that goes that extra mile, so thank you and thank your colleagues too. Would it be too ealry to believe I may have finally found a company that's realised that while cheap and cheerful has it's place, quality workmanship and support from soup to nuts is something that is growing in demand. I've looked through your forums and currently it seems (unless I missed something which I'm not incapable of doing being only human and all) the vast majority of threads are asking for help in understanding things and how to use the hardware, rather than complaints or issues with the hardware itself. I looked for reviews and other than a small issue here or there that was more to do personal preference than the hardware itself, I've yet to find a negative review.

                Products are definitely on my shopping list once I get this powering issue sorted out. You'd think someone would already have something sorted to supply 5V from mains that didn't require more plug sockets than most entire houses possess just for a multi board Arduino project.

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                • #9
                  Seems that once you know what to search for there are plenty of ways people have done this very thing already. Several examples of using atx power supplies can be found here: http://www.instructables.com/id/Ency...pply-Conversi/

                  This really had me scratching my head until I'd already thought of using a PC PSU, then everything fell into place. Hopefully me putting this here will make it easier on the next newbie who comes along trying to work out how to power everything.

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                  • #10
                    becareful with cheap psu's that fluctuate voltage, get a good quality ATX psu, I use a picoPSU 120W DC-DC psu with ~10-30 input and output is 12V 6A, 5V 6A. 3.3V 6A, it's also smaller than an arduino UNO

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                    • #11
                      Originally posted by tonton81 View Post
                      becareful with cheap psu's that fluctuate voltage, get a good quality ATX psu, I use a picoPSU 120W DC-DC psu with ~10-30 input and output is 12V 6A, 5V 6A. 3.3V 6A, it's also smaller than an arduino UNO
                      Thank you for the tip, I'll certainly have a good look at them. New multimeter arriving Monday so that should help and I've got my eye on a reasonably priced oscilloscope for a different project. Heh... at this rate I'll have a fully equipped electronics rework station and wood working shop the way these projects are going.
                      Last edited by Eewec; 26th June 2016, 05:28 PM.

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