keypad interfacing

Discussion in 'The Projects Forum' started by ms_kishor4u, Oct 20, 2008.

  1. ms_kishor4u

    Thread Starter New Member

    Oct 17, 2008
    hi to all;
    is there any method for the key pad scanning using interrupts. how to do keyscan in the interrupt. pls give me some ideas...
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    Have a look at this short explanation of keypad scanning. In the article there is brief mention of the use of a 3-input NAND that can be used to produce what is sometimes refered to as an "any key pressed" signal. Feeding the output of the NAND to an external interrupt pin on the microcontroller will provide you with a means of detecting that a key has been pressed.

    There are a couple of ICs made by National Semiconductor that can be used to interface to a row/column organized keypad. I believe the part numbers are 74C922 and 74C923. The main difference between the two ICs is the number of switches they support.