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  • Maximum distance between 4D screen and Arduino

    Hello,

    I have a 4D systems 70-DT-AR screen and I was wondering if there is a maximum distance between the screen and the arduino that should be respected in order for the display and touch modules to work correctly ?

    Kind regards,
    Oumy

  • #2
    Hi Oumy,

    Its a UART serial interface at 3.3V levels, so really the wiring between the Arduino and the display should not be very long. I don't have specific lengths I can recommend, but the longer the cables are the larger the voltage drop and likely also the slower baud rate you might have to use, potentially also the larger risk you have of noise/interference getting into the serial stream and causing problems. Typically UART Serial would be within a meter sort of distance, ideally shorter I would suspect, but you might get a way with a little longer. Very environment dependant I would thnk.
    If you need to go longer then that is where RS232 would come in, you would need an RS232 transceiver on each side then you can go 10m or so. If you need to go even longer, then RS485 could be used - however that is typically half duplex for 2 wire, but you can get full duplex for 4 wire systems (half is where only one side can talk at a time, and full is where both can talk at a time as they are on a differential bus, not separate RX and TX like UART and RS232 is - which is full duplex).
    Hope that helps a little bit.

    Regards
    James

    Comment


    • oumyth
      oumyth commented
      Editing a comment
      Hi James,

      Thank you for your help !

      Ideally, my screen would be 0.54 meter away from my Arduino.
      UART Serial having to be within a meter of distance, would that mean I would have no problem related to the distance with 0.54 m ?

      Best regards,
      Oumy

  • #3
    Hi Oumyth,

    I cannot guarantee you will be without problems, its very dependant on what environment you are in, you are going to have to try it with that cable length and see how you go. If you do have problems you can try to lower the baud rate from say 200000 baud down to 115200 and see if that helps.

    Personally I would think 0.5m or so should be OK, but if the wires are draped over the top of a motor or past a welder etc, then you will no doubt have problems. I do not know what application you are using this in, so its very hard to know if it will be OK.

    The other issue you might have is the powering of the 7" display over these same cables. How are you going to be powering the display? From the Arduino's built in regulator, or are you planning on feeding an external 5V source into the 4D Arduino Adaptor using the H2 header and moving the jumpers? If you are attempting to use the Arduino's built in regulator, and powering the Arduino off its Barrel Jack with say 12V, then likely you will have issues as the 7" can not be powered from the Arduinos regulator at the best of times (however this is Arduino model specific) as it cannot supply enough current.

    I hope that makes sense

    Regards
    James

    Comment


    • oumyth
      oumyth commented
      Editing a comment
      Hello James,

      Thank you for your fast reply !

      I will try lowering the baud rate if I do have problems.

      To sum up my project, my screen will be fixed up front a locker. At the back of the locker, I'm placing the Arduino, which I'm thinking of powering up with its barrel jack. The wires between the screen and the arduino circulate through a cable conduit fixed to the locker. The Arduino, on the other side, depending on what the user touches in the screen, controls different locks controlling the opening and closing of the different lockers.

      Since my current 5-way cable is too short, I'm thinking of cutting it in half and weldering the in-between. If you think welder would make me have problems, do you have any reference of a 5-way cable that is at least 0.5 m ? I have submitted a ticket to the Sales, but I didn't get any reply since.

      I was thinking of connecting H1 to the display, and connecting the RX pin of J3 and TX pin of J4 to RX1 and TX1. When uploading the program, I would connect the display to my computer through H2. Once the uploding finishes, I thought I could just disconnect H2. Since, as you said, that wouldn't supply enough current, do you have any picture of how I should connect the H2 header to an external 5V source ?

      Best regards,
      Oumy

  • #4
    Cutting a 5 way cable in half and soldering 5 wires in between the 2 ends to make it longer, should be fine. These are just straight wires, no noise immunity anyway, so you should be OK there. I am not aware of longer cables off the shelf, we have these custom made and we likely can get longer ones made on request, but there would be a MOQ - something you will need to discuss with sales.

    You cannot program through H2, that is not how it works. H2 is only there to provide a header to connect external power. Please refer to the Arduino Adaptor Shields datasheet, there are full details in there.

    https://4dsystems.com.au/4d-arduino-adaptor-shield-ii
    Datasheet: https://4dsystems.com.au/mwdownloads...ad/link/id/85/

    To program the display, you must connect directly to the display with the programmer, so the Arduino is disconnected, otherwise it would be chatting on the line while you are trying to program the display, and programming will fail. You will be able to program the Arduino with the display connected still if you use RX1/TX1 of the Arduino to J3 and J4 as you said, as the Arduino programming will go through its RX0/TX0 so wont cause problems with the RX1/TX1 pins.

    To make H2 work for external power, you move the jumper above it relating to the power (PWR) from the AR (Arduino) side, to the PR side. Its labelled as 4D Prog Cable/Adaptor to indicate you can plug a 4D Programming Cable or Adaptor in there to provide power. You cannot program through that though. RX and TX are not actually connected on H2 (The silkscreen markings should not be there really).

    You are welcome to try and power the Arduino off the barrel jack with 12V, and power the display from the Arduinos' 5V line, but you might find the display flashes and wont start up, or the regulator on the arduino will get very hot due to the current draw of the 7" display being powered off it, and you might encounter problems - but it is very Arduino specific, things might have improved on the Arduino these days and the regulator might be better. But if it doesnt work, then really you need to provide the 5V to the display from a different supply, which is where H2 on the adaptor comes in, so you can feed 5V and GND into there, while the display is connected to H1, and the display will be powered off the 5V external supply rather than from the Arduino.

    Hope this helps.
    James

    Comment


    • oumyth
      oumyth commented
      Editing a comment
      Hello James,

      Thank you for your reply !

      I will wait for the sales' reply to know when they could make a custom made 5-way cable. If the delay is too long I will cut in half and solder the two ends.

      So, if I understand well (if not, please tell me), to connect the adaptor to an external power supply I will need to :
      - Connect the 5V and GND from H2 to the power supply.
      - Put a jumper wire between PWR from J2 to PR from J2.

      Best regards,
      Oumy

    • oumyth
      oumyth commented
      Editing a comment
      Hello James,

      I would like to know the current needed from the external power supply to power off the display.

      Best regards,
      Oumy

  • #5
    Hello again,

    Originally posted by oumyth View Post
    So, if I understand well (if not, please tell me), to connect the adaptor to an external power supply I will need to :
    - Connect the 5V and GND from H2 to the power supply.
    - Put a jumper wire between PWR from J2 to PR from J2.
    Yes you connect 5V and GND to the 5V and GND pins on the H2 Header.
    Yes you simply move the little jumper shunt that comes on the J2 header, from the Left side (AR) to centre, over to the right side (PR) to centre. So the Power comes from the H2 header instead of coming from the Arduino itself. Note this is only to power the display. This is not also powering the Arduino - in case this was not clear.

    The current required to power the display on 5V is listed in the Datasheet for the display you have. You have said in your first post that you have "70-DT-AR" however I am unsure if that means you have the uLCD-70DT or if you have the gen4-uLCD-70DT. The -AR extension just means it has the Arduino Adaptor in the kit etc. I would suggest you have a 5V power supply which can supply at least 1A to 2A of current @ 5V. The figures stated in the datasheet are 'typical' and also averages, it does not consider any inrush current, or potential maximums.

    I hope that helps.
    James

    Comment


    • James_4DSystems
      James_4DSystems commented
      Editing a comment
      You are very welcome. I hope your project works out as you hope. Please keep us posted.

    • oumyth
      oumyth commented
      Editing a comment
      Hello James,
      Thank you for your kind hope !
      I have another question. I need to connect the adaptor's GND to the external power supply's GND - but do I need to connect it also to the Arduino's GND pin ?
      ( I had to do this for my card reader, but not for my locks. Since I can't do tests before a week (display not with me until then) I wanted to make sure of this before printing my printed circuit.)

      Best regards,
      Oumy

    • James_4DSystems
      James_4DSystems commented
      Editing a comment
      Hi Oumy,
      You connect 5V and GND to the H2 header to power the display, and then your USB or barrel connector to the Arduino.
      The reason you need common ground is so the 5V and the 12V (or whatever you are powering the arduino with) is referenced off the same value.
      You cant just connect 5V wire only from the power supply as it has no reference, as voltage is the potential difference between 2 wires.

      Alternatively, if you want to just use 1 supply, you could power the Arduino and the display from your external 5V supply, if you connect 5V and GND to wires into the 5V and GND headers sockets on the Arduino (or Shield), with the J2 back into the AR position. Depends how you want to go about it.

      What circuit board are you referring to?
      Are you not going to be using the 4D Arduino Adaptor?
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