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Thread: 1602A LCD display brightness

  1. #1

    1602A LCD display brightness

    Hi. Followed the setup here - connected to teensy 3.6. I am powering the LCD display from the +3.3v output on the teensy board. Test "hello world" is working, but the display
    is not very bright, even with full contrast. Is that because the display is supposed to power off of 5V?


  2. #2
    Senior Member+ Theremingenieur's Avatar
    Join Date
    Feb 2014
    Colmar, France
    You have given the answer yourself, at the end of your question.

    Depending on your LCD’s brand and model (these are built by many different manufacturers), it might work with a 5V power supply on one side and 3.3V logic levels on the other side but you can’t take that for granted. Thorough study of your specific LCD is required. Afterwards, you could still add a 74hct125 or 74hct245 as a level shifter, if required.

  3. #3
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Quote Originally Posted by lamikam View Post
    Is that because the display is supposed to power off of 5V?
    Most likely yes. Almost all those very old character displays were meant for 5V.

    The good news is nearly all of them also have "TTL level" inputs, so they can almost always work with Teensy's 3.3V outputs even when running from 5V.

    Just make sure you use the 6-pin constructor for the library (the shortest, simplest one), where the signals are always in the direction from Teensy to LCD, where you connect the LCD's R/W pin to GND. The normal LiquidCrystal library never tries to read status from the LCD anyway.

    But if you use LiquidCrystalFast with the 7 pin version, you would need proper level shifters between the LCD and Teensy 3.6. That one really will drive R/W high in some cases, causing the LCD to send a 5V signal for status back to Teensy. Since Teensy 3.6 is not 5V tolerant, that case could lead to damage.

    As long as the R/W pin is connected to GND, and you're careful not to accidentally touch any signal wire to 5V, these displays running at 5V are safe to use with Teensy 3.6.

  4. #4
    Yeah, it is an old display. Thanks

  5. #5
    So I tried powering the display with the +5V from the teensy 3.6 board, and the display appears the same as is shown in the picture on this post -

  6. #6
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    How would you like me to help?

    Many years ago (before Teensy 1.0) we sold some of these LCDs for 8051 boards, but haven't really carried any product like that since.

    On that other thread, I was able to confirm the LiquidCrystal library does indeed work on Teensy 3.6, even using those specific 6 pins. That was possible because I have boxes of hardware for testing many of the widely used libraries, and luckily we saved some of those old LCDs for this sort of test.

    But for some random LCD I know nothing about, not even a part number, and which didn't come from PJRC... what do you imagine I can do here? I'm not clairvoyant or psychic. I can't even tell whether you have one with a backlight built in.

    If the LCD is working (showing text properly) but the backlight isn't bright enough or the contrast is low, maybe you should contact the vendor who sold it?

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