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Thread: How about a 3.5 inch 480x320 tochscreen display?

  1. #51
    Senior Member+ Frank B's Avatar
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    If the day had 48hours I'd really like to try one of these RGB to HDMI or data-to HDMI chips on a T3.6
    But that's impossible at the moment. Maybe next year.. i guess at least RGB to HDMI is somehow possible on the 3.6

  2. #52
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    Just taking a peak at the datasheet for the ILI9488, looks like it has Backlight control built in along with a PWM_OUT pin to drive the backlight LED. That would save us from needing a pin to PWM the Backlight. We would just have to add a fet to the breakout.

  3. #53
    Senior Member+ Frank B's Avatar
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    @Paul, any news ?

  4. #54
    Senior Member PaulStoffregen's Avatar
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    Nope, sorry, I put this on hold for a while. Too many other urgent projects....

  5. #55
    You can also consider the ili9481 displays I am able to control the display with a Teensy 3.5 in 16 bit mode at 65k colors(RGB565). with very fast screen updates.



    I able to write all 16 IO pins:

    Code:
    void ILI9481_t3::setIO(uint16_t data)
    {
        // lower 8 bits
        GPIOD_PCOR = 0xFF;
        GPIOD_PSOR = data & 0xFF; // DB 7, 6, 5, 4, 3, 2, 1, 0
    
        // upper 8 bits
        byte a = data >> 8;
        (a & 0x80) ? (CORE_PIN31_PORTSET = CORE_PIN31_BITMASK) : (CORE_PIN31_PORTCLEAR = CORE_PIN31_BITMASK); // DB_15
        (a & 0x40) ? (CORE_PIN32_PORTSET = CORE_PIN32_BITMASK) : (CORE_PIN32_PORTCLEAR = CORE_PIN32_BITMASK); // DB_14
        (a & 0x20) ? (CORE_PIN29_PORTSET = CORE_PIN29_BITMASK) : (CORE_PIN29_PORTCLEAR = CORE_PIN29_BITMASK); // DB_13
        (a & 0x10) ? (CORE_PIN30_PORTSET = CORE_PIN30_BITMASK) : (CORE_PIN30_PORTCLEAR = CORE_PIN30_BITMASK); // DB_12
        GPIOA_PCOR = 0x3C000;
        GPIOA_PSOR = (a & 0xF) << 14; // DB 11, 10, 9 , 8;
    }

    I am still trying to make it work in 262k mode though.
    Last edited by roomtek; 07-28-2017 at 09:21 PM. Reason: code update

  6. #56
    Senior Member+ defragster's Avatar
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    Waking this thread until a better answer … the T4 Beta thread shows interest in a larger display - the ili9488 is functional on T_3.6 and T4 - but 18 bit color is too many bytes for fast SPI updates - and the with a couple different 9488's under test - some seem to have issues. Touch XPT2036 works - but Display I got like Paul's {p#1470&1473} shows MISO not tristated - so reading Touch means cutting/not connecting the TFT's MISO then it works with write only display. Most recent notes cluttering T4 thread are here XX

    The ILI9488's so far all want 18 bit color - if one were 'wired' to accept 8 and/or 16 bit that would drop the RAM/SPI hit - the PDF says it can be selected - but it seems there must be hardware bits set as well that preclude attempts to use 16 bit mode. So a better package is needed - 3.5" would be nice - higher res than 240x320 optional as 320x480 pixels are higher DPI and more numerous. Came across one that "works" on rPi - except it is missing the D/C pin and the PDF didn't show me commands/data working without that control bit?

  7. #57
    Senior Member+ Theremingenieur's Avatar
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    I guess that it it’s time to think about a “Teensy G”, a graphics (sub-)processor which would communicate with whatever “main” Teensy through a simple command set, similar to the gfx libraries and which would then care about rendering, frame buffering and efficient high-speed communication with the TFT, taking all that load away from the principal MCU.
    For 320*480, 24bit RGB (thinking for the future) and 8 bit alpha, one frame buffer would take 614400 bits of RAM...

  8. #58
    Senior Member+ MichaelMeissner's Avatar
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    Some time ago I collected links of various displays, including displays that have a smart processor on them. Some are a little on the pricey side.

    Vizic Technologies


    Newhaven Display


    Gamedunio


    Raspberry Pi controlled display
    One option might be to use the Raspberry Pi as the driver. Unfortunately it can at times be hard to source the cheaper, smaller, less power hungry Pi Zero W in quantity (usually it is $5-10 for one at my local Microcenter, but the price goes up if you buy more than one, and in some places only quantity 1 orders are allowed). Lets see:
    • Rasberry Pi Zero W: $10
    • 32GB micro SD card: $4
    • ebay 3.5" resistive touch HDMI 480x320: $20



    I suspect the Newhaven displays are probably the best for interfacing with Teensy.

  9. #59
    Senior Member+ Frank B's Avatar
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    The T4 already has a GPU with a fast interface. Paul mentioned a larger variant... my hope is, it has the required pins, then.. even if the GPU is not very powerful - the interface alone would be very helpful.

  10. #60
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by Frank B View Post
    The T4 already has a GPU with a fast interface. Paul mentioned a larger variant... my hope is, it has the required pins, then.. even if the GPU is not very powerful - the interface alone would be very helpful.
    Though I imagine there you want to get into having the ability to share memory with the display and/or use more pins in parallel to get around the SPI knothole of serially transferring 1 bit at a time.

  11. #61
    Senior Member+ Theremingenieur's Avatar
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    Without having looked it up, I’d guess that in the meantime, a few TFT controllers with QSPI interface should be available, thus making the bottleneck four times wider...

  12. #62
    Senior Member+ Frank B's Avatar
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    it is a parallel interface, configurable.

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