8*8 matrix keypad and relay connection

Discussion in 'Embedded Systems and Microcontrollers' started by santu, May 15, 2011.

  1. santu

    Thread Starter New Member

    Dec 23, 2010
    hello , i am using a- 8*8 matrix keypad
    mcu at89s52
    8*8 relay matrix
    my problem is that i have no idea regarding the current flow in this kind of circuits, so please give me sufficient information on this. i have attached circuit diagram of 8*8 relay matrix which i got from you.please reply me quickly i am in the middle of my project.thank you waiting for your replies
  2. terra

    New Member

    May 12, 2011
    normally current through output port due to low imopedence
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    The 2803 can handle around 400-500 mA. 500 is listed as the absolute MAX.

    The datasheet uses 100, 250, 300, and 350mA in its parameter tests, so those should be safe values to use for that chip.

    What are you driving with it? inputs to other active devices seldom need such extreme currents, but things like LEDS and relays do.

    Edit: never mind, I found the title on the drawing says relay matrix. :)
  4. santu

    Thread Starter New Member

    Dec 23, 2010
    pleae tell me the difference between uln 2803 and udn 2982 in a descriptive way.
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    Use the device numbers to search for data sheets.
  6. santu

    Thread Starter New Member

    Dec 23, 2010
    i have gone through th datasheets but can't understand the functionality of udn2982.please reply so i can start my programing
  7. Alberto

    Active Member

    Nov 7, 2008
    UDN2982 is the high side controller. This device will control the columns of your matrix while ULN2803 is the low side controller and is responsabile to control the raws.

    To control the matrix you will need two bytes, one byte for the colums and one byte for the raws. Give to these two bytes the value of one and you will activate relay #1, give the two bytes the value of 128 and you will activate the last relay.
    Any other number from 1 to 255 will activate a combination of the 64 relays. (I leave to you the pleasure to discover the coding)


    Last edited: May 24, 2011