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Thread: ILI9341 Color TFT 2.8 touchscreen question

  1. #1
    Junior Member Nikki Cooper's Avatar
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    May 2019
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    ILI9341 Color TFT 2.8 touchscreen question

    Hi!
    I have a couple of the ILI9341 Color TFT 2.8 inch touchscreens that were recently purchased from the pjrc store.
    Looking closely at the TFT PCB I notice its LED circuit is the following:

    2.8" TFT color display LED control circuit

    Simple enough. Given the above circuit which is already on the display PCB, I would like a confirmation that it is O.K. to connect Digital pin 6 (physical pin 8) on Teensy 3.2 directly to the LED pin on the display, dispensing with the usual 100R resistor between +5V VCC and the LED pin. As you have likely already surmised, I hope to use the PWM modulated output of the Teensy to control the display backlight brightness. Yes, I've searched for previous posts on this topic, and it seems some have successfully done this. From what I can tell, it completely depends on who designed a given display implementation, some have the LED backlight control electronics built in (like my display appears to have) and some don't. I'm almost positive I can do this safely but I've already managed to kill a Teensy 3.2 when attempting to interface to it via a simple high side switching circuit completely unrelated to the display due to a totally brain dead dumb mistake. So I'm going to be extra cautious just in case I'm misunderstanding whats going on here. Teensy is very unforgiving. Not a fault, but rather the nature of the beast. A nod of yea or nay from you experienced grey beards would be greatly appreciated.

    TIA,
    Nikki

  2. #2
    Senior Member+ defragster's Avatar
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    No idea - but would a safe [and sufficient] test be to feed 3.3V through DMM measuring the current it draws lighting the display?

  3. #3
    Junior Member Nikki Cooper's Avatar
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    Thank you for your reply. While I did not follow your advice, it did serve to motivate me to analyze things a little closer. Once I took into account the fact that the display has it's own 3.3V regulator, I realized my fears were unfounded and overly paranoid. I can report that connecting the display LED pin to Teensy PWM modulated output, the LED brightness control works smoothly and flawlessly. I think that the PJRC store documentation for the display should be updated to reflect this. It is very easy to confirm whether the display has the brightness control electronics or not. I sure there were probably earlier displays that didn't have this capability.

    I think I was just being a little bit too cautious and paranoid due to my earlier mishap with the first Teensy I managed to blow up.


    Nikki

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