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Thread: 2.8 ILI9341 restive touch miso not connected ?

  1. #1
    Senior Member+ Frank B's Avatar
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    2.8 ILI9341 restive touch miso not connected ?

    Hi,

    i have a "ILI9341" 2.8'' Display with resistive touch from china (aliexpress).
    The model is "TJCTM24028-SPI". The board looks like the boards on the smaller displays, but with the additional touch-ic (currently unused and not connected).

    The graphics-test runs fine, display works and shows the graphics.
    But strange is, SDO(MISO) seems to be not connected ? The diagnostic output is all 0xff, sometimes 0x00.

    Display Power Mode: 0xFF
    MADCTL Mode: 0xFF
    Pixel Format: 0xFF
    Image Format: 0xFF
    Self Diagnostic: 0xFF



    Is my display defective, or are there exsisting variants without connected miso ?
    Does anyone but me see this behavior with these displays?

    Normally, this shouldn't be a big problem, but i want to read display content back..

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Good question.

    I recently ordered some of these displays. Haven't used them yet. I made this PCB to speed things up (well, at least minimize my time spent fiddling).

    https://www.oshpark.com/shared_projects/TG395I75

    Still waiting for the PCB to arrive from OSH Park, so this is untested. I should have it next week...

  3. #3
    Senior Member+ Frank B's Avatar
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    I think i'll order some of these boards! Do you plan a version with audio-board(/memoryboard) compatible connections or jumpers ?

    I'll try my 2nd display at the weekend.
    Is there a existing library for the touch controller, or do we have to write our own ?
    At a quick glance, the controller is not much more than analog/digital converter(s).

  4. #4
    Senior Member+ defragster's Avatar
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    Paul - that is just a more pin exposed version of the 'purple test board' from the ILI9341 page? And some added components?

  5. #5
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    Ok interested, ordered boards from oshpark and some TJCTM24028-SPI displays. Seems like I spend half my development time trying to come up with a display option that does not require "time spent fiddling".

  6. #6
    Senior Member PaulStoffregen's Avatar
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    The boards just arrived from OSH Park.

    At this moment I'm wrapping up work to release the new bootloader chips. Once that's done, I'll build and test one of these with the display.

    The added components are two 10K resistors, as pullups on the two CS signals. I really should have put one on the original test board's CS signal. These bigger displays have 5 extra pins for the touch controller chip. I just routed the SPI signals and 2 pins for CS and INT. If the board works, I'll do to the trouble of updating that OSH Park page with good documentation.

    If the display actually works well, odds are good I'll write a library for its touch controller chip and PJRC will probably start stocking this display too. We really need a somewhat larger display with touch that's affordable. I'm hoping this will be the one!

  7. #7
    Senior Member+ Frank B's Avatar
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    I just connected my 2nd display ( fiddling..:-) , this one works as expected - including miso.
    So, all is ok.

  8. #8
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by PaulStoffregen View Post
    The boards just arrived from OSH Park.

    The added components are two 10K resistors, as pullups on the two CS signals. I really should have put one on the original test board's CS signal. These bigger displays have 5 extra pins for the touch controller chip. I just routed the SPI signals and 2 pins for CS and INT. If the board works, I'll do to the trouble of updating that OSH Park page with good documentation.

    If the display actually works well, odds are good I'll write a library for its touch controller chip and PJRC will probably start stocking this display too. We really need a somewhat larger display with touch that's affordable. I'm hoping this will be the one!
    Looking forward to results on the updated OSH board - had the old one in a waiting cart . . .

    That looks like a nice upgrade to the ILI9341 in the store now - and only minimally higher cost? Supported touch on known good units and larger screen area ++good++. Found 'some' on aliexpress not noted - assume like FrankB's it is a Resistive touch unit like the $35 Adafruit - not Capacitive like the $45 unit?

    Also ++good++ any other board that makes prototyping/connecting easier - like those from your ILI9341 YouTube Demo I asked about -
    "custom proto boards. I just drew up PCB layouts and sent them off to one of the cheap Chinese PCB fabs. I believe it was probably iTead. They have a cheap 100 piece price. I also laser cut a big batch of matching plastic bases and tapped threaded holes, which goes much easier and faster as a big batch."

  9. #9
    Senior Member PaulStoffregen's Avatar
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    I'm happy to report the OSH Park board works.

    At least the display part. Haven't tried to use the touch controller chip yet.

    Click image for larger version. 

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    (click for full size)

  10. #10
    Senior Member+ defragster's Avatar
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    Good news, if you get any sanity check on the touch wiring I'll proceed to order. I see you built the power side too - but running on USB in this pic - expect that works as well using the old part info?

    By any chance does the current PJRC store ILI8341 pinout work on that same OSH board?

  11. #11
    Senior Member PaulStoffregen's Avatar
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    The first 9 pins are the same, so the smaller display should work if plugged in to those 9 pins. But I haven't actually tested that.

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    Senior Member+ Frank B's Avatar
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    This evening, i managed to kill my teensy which is soldered to the 2.8'' display (my own mistake).. arghh..
    I wanted to connect the touch-controller tomorrow and maybe start with coding..

    What's the best way to remove a soldered teensy ? Sawing the board near and between the pins with a dremel and desolder the remaing small parts ? Or are there better ways ? Under the teensy is a fully assembled memoryboard and the audioboard, then a board with the display.. all tightly soldered together :-(
    Last edited by Frank B; 10-10-2015 at 10:40 PM.

  13. #13
    Senior Member PaulStoffregen's Avatar
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    Oh, that's painful. Desoldering is tough work. Usually I cut the pins and pry away the plastic. Then I heat them one at a time and pull the pin out with tweezers. Even that way, getting the leftover solder out of the hole with wick is difficult.

  14. #14
    Senior Member+ defragster's Avatar
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    Great news on the 9 pin compatibility - not only the OSH board but the touch screen with common ILI9341.

    Bad news Frank - if you get medieval on the Teensy and can save the pins and the underboards you'd cut your losses - as long as you can cut just the Teensy with the close contact. My limited experience at cleaning pins only works about 1 at a time - then they go cleaner and not too much heat - especially with the other boards and solder so close.

  15. #15
    Senior Member PaulStoffregen's Avatar
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    The touchscreen works.

  16. #16
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by PaulStoffregen View Post
    The touchscreen works.
    That is good news! I'll finally finish my OSH order with a set of those then - and wait for PJRC to stock the ILI9341_Touch.

    Does that ILI9341_Touch display have the SD card reader on? Any chance it will work more directly than the old ILI9341?

    Paul: The PJRC MicroSD reader - I just got two and the first powered up and works just fine! IIRC You noted somewhere of a new version with a second pull-up, is that important for reliable use?

  17. #17
    Senior Member PaulStoffregen's Avatar
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    I've started a library specifically to support the XPT2046 resistive touch controller chip.

    https://github.com/PaulStoffregen/XPT2046_Touchscreen

  18. #18
    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by PaulStoffregen View Post
    I've started a library specifically to support the XPT2046 resistive touch controller chip.

    https://github.com/PaulStoffregen/XPT2046_Touchscreen
    Great !

    Is the "t-irq" pin useful ?

    Horror on sunday:
    Click image for larger version. 

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    ..i forgot to mention the "connectorboard" and the rtc-crystal :-)

  19. #19
    Senior Member PaulStoffregen's Avatar
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    The T_IRQ line might be useful if you want the display to wake up your processor.

    No software support is needed in the library. It automatically goes low when the display is touched. It can also go low when the library reads the display. So to use it, you *stop* calling the library and then use attachInterrupt or otherwise arrange for the falling edge to wake up. Obviously you'd disable the interrupt after waking up, before you use the library again.

  20. #20
    Senior Member PaulStoffregen's Avatar
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    Here's the interactive example....

    Click image for larger version. 

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  21. #21
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    Very interesting! Can anyone recommend a source for this display? Does it have a SD card reader also? (...and did Paul really post that at 4 am?)

  22. #22
    Senior Member Wozzy's Avatar
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    Very Nice.
    I had a similar display already setup from my BMP280 project.
    I downloaded the new Touchscreen Library and had it working in less than 10 minutes.
    It seems much more precise than the previous touch library I was using.
    Click image for larger version. 

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    Thanks Paul!!

    I never finish any project because fun stuff like this always sidetracks me! :-)

  23. #23
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by Wozzy View Post
    I never finish any project because fun stuff like this always sidetracks me! :-)
    I feel that way too sometimes! This is kinda sidetracking me from work on a motion sensor library, and a number of other things like investing what's up with the latest MacOS.

  24. #24
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by JBeale View Post
    Can anyone recommend a source for this display?
    Eventually we'll stock them, like we do now for the smaller one.

    But really, we just get them in bulk from China. We do test them. So far, most batches of the smaller one have had a few we discard, sometimes because they don't work, sometimes because they have a cosmetic flaw. Other than testing, it's (probably) exactly the same thing as if you get it directly from a Chinese merchant.

    You can find these from lots of merchants on ebay and aliexpress. I'd recommend getting a spare.

    Does it have a SD card reader also?
    Yes, but at least the one I have here seems to have 1K series resistors. Those will need to be shorted to allow 24 MHz SPI.


    (...and did Paul really post that at 4 am?)
    Yup, closer to 5am actually.

    I often do software development in all-night sessions, when it's quiet.
    Last edited by PaulStoffregen; 10-11-2015 at 07:55 PM.

  25. #25
    Senior Member PaulStoffregen's Avatar
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    I'm considering adding oversampling to this library.

    The rapidly switching signals for the TFT do capacitively couple to the resistive touchscreen signals. Occasionally they cause a significant error in the touch reading, and frequently they add a small amount of noise.

    Does anyone know of any good algorithms for correlating the 2D position of multiple point and rejecting "bad" measurements?

    For example, I considered taking 3 measurements and computing the distance between each of the 3 pairs, then keep the 2 with the shortest distance and take the average between those 2. Or maybe 4 measurements....

    This seems like the sort of thing that would have an optimal algorithm published. My google searches are turning up tons of unrelated stuff...

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