+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Newbie level 4
    Points: 37, Level: 1

    Join Date
    Nov 2012
    Posts
    5
    Helped
    0 / 0
    Points
    37
    Level
    1

    8*8 LED Matrix and Teensy

    Hello guys,

    This is my first post here, "plus" a newbie, so please be nice :P

    So I have 64 White LEDs multiplexed. I tested my matrix by connecting each column to GND and +5v (from Teensy) to each row one by one "without resistor". All worked well.

    Let me explain why without resistor.
    Before making the matrix, I tested all the LEDs with a 330ohm resistor in series and none light up, although all were working fine without a resistor. So I guess my LEDs are high-voltage ones...
    (I tried decreasing the resistor value.. By putting 10x330ohm resistors in parallel, only then they were working, otherwise not.)

    OK, so I tested my LED Matrix without resistor, all worked fine with a +5v source from Teensy.

    Now the problem comes when I connect each row to an "output" pin on Teensy and all the column to GND and program the code to produce HIGH one by one on each row.
    This doesn't work! =/

    To test if my code was working fine, I removed my matrix and placed single LEDs to those outputs and they worked fine. =/

    Please help me out!

    •   Alt12th November 2012, 10:59

      advertising

        
       

  2. #2
    Full Member level 5
    Points: 3,218, Level: 13
    Achievements:
    Created Blog entry 7 years registered
    udhay_cit's Avatar
    Join Date
    May 2008
    Posts
    319
    Helped
    36 / 36
    Points
    3,218
    Level
    13
    Blog Entries
    1

    Re: 8*8 LED Matrix and Teensy

    are you connecting this LED'S to the microcontroller pin directly? are you using any transistor switch? which microcontroller you are using? Give me your circuit diagram....

    Micro controller pins will handle only upto 25mA(this is for pic & may vary for diff type of uC) & if the current exceed it could damage the port pin...

    Connect the anode of the LED using some low value resistor(10E to 100E) to the +5V & use ULN2003 to drive the cathode points...

    http://microcontroller51.blogspot.in...lay-board.html
    http://www.picbasic.co.uk/forum/showthread.php?t=7457
    www.google.com


    2 members found this post helpful.

    •   Alt12th November 2012, 11:16

      advertising

        
       

  3. #3
    Newbie level 4
    Points: 37, Level: 1

    Join Date
    Nov 2012
    Posts
    5
    Helped
    0 / 0
    Points
    37
    Level
    1

    Re: 8*8 LED Matrix and Teensy

    Yes i'm connecting them directly to the microcontroller. :s It's 'Teensy 2.0' (Arduino)

    10E? 10ohm?

    Okay, from ULN2003's datasheet, I can see that ULN2003 has 7 transistors. Is there any other IC that has 8 transistors? If not, then I think I have to use one separate transistor.
    It has "NPN Darlington Transistors". What other information (specs) do I need to tell at shop to buy that one similar transistor?

    Thanks for the hep :)

    EDIT:
    P.S. I just want one LED to light up at a time in the whole matrix, not a full row/col. Why do I still need a transistor?
    Last edited by aly.yousuf7; 12th November 2012 at 11:57.



    •   Alt12th November 2012, 11:40

      advertising

        
       

  4. #4
    Full Member level 5
    Points: 3,218, Level: 13
    Achievements:
    Created Blog entry 7 years registered
    udhay_cit's Avatar
    Join Date
    May 2008
    Posts
    319
    Helped
    36 / 36
    Points
    3,218
    Level
    13
    Blog Entries
    1

    Re: 8*8 LED Matrix and Teensy

    You can use use 10ohms to 100 ohms... i suggest 47 ohms...It may vary with ON time of the LED & brightness you required...
    For 8 transistors you can use ULN2803...

    If you are increase the number of LED then you have to reduce the resistor because it will take higher current. As per ohms law (R=V/I look the relation bw R,I) you have to increase the resistance value for single LED.

    Regards
    Udhay



--[[ ]]--