4x4 keypad without microcontrollers ?

Discussion in 'Homework Help' started by natrix, Mar 24, 2009.

  1. natrix

    Thread Starter New Member

    Mar 24, 2009
    I am working on a project for (digital design) , that requires me to use a 4x4 keypad the problem is that the keypad has only 7 lines like the following sketch

    There is obviously 16 key on it , the question is how to take there output on 16 lines ? using digital gates and wires only !!!
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    How do you only count 7 lines? Or is your actual keypad different from the illustration?

    Make a truth table based on which key has been pressed, and which lines are connected by the key. Add pullup resistors to the rows and ground to the columns, and there you are electrically.
  3. lightingman

    Senior Member

    Apr 19, 2007
    Look at the 74HC922. It wil scan and decode a 4 x 4 keypad and give 4 bit binary output and a key-down output.

  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    The process is pulling a column high, with the other three low, and check for a high on any of the row wires. Then shift the high column left/right by one, check for any high outputs, and repeat.

    When a high output is found, note the column: A, B, C, D (4321 in your diagram), and which row, 1,2,3,4 (4321 in your diagram) that had the high voltage on the scan for which key is down. Debouncing is the same, check if 3 "scans" show the same key down, the scanning of the other columns provides the delay.
  5. natrix

    Thread Starter New Member

    Mar 24, 2009
    sorry I ment 8 lines anyway thanks for all of you