18F4550 with 74LS138

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    I am trying to connect 127 switches to the microcontroller using three 74ls138  decoders how will I scan the switch for buttons pessed


    Ligo George

    You may use it like matrix keypad. Use 6 pins of PIC as inputs such that you can connect 24 x 6 = 144 switches.



    I used the program in the tutorials on the 4×4 keypad as an example I modified it to scan the rows using the 74LS138 but I can not get it to work properly. I attached the I used. Please let me know what I am doing wrong.

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