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  • Pic® Basic

  • Using a 2 x 16 LCD Address Lines as Button Inputs

    Mark Rodgers G0EBB 20,01,03

    The above circuit uses a PIC16F877 but it will work with any PIC® you choose, the file that supports the hardware will need to be changed to suit the pins chosen for the address lines you use on your PIC®.
    This diagram must be used with LCD_KEY.BAS.

    How it works

    The connection of the LCD is as standard and this circuit and software can be very easily used in any existing project or new one. The buttons do not interfere with the operation of the display in any way.

    The four 10k resistors hold the address lines high and the 1k resistors are to limit the current in case of errors (i.e. two pins trying to pass current through the switch).
    The buttons could easily be any external signal that is normally open and does not carry any power of its own.

    The software is very simple and works as follows;

    1, Make RC1 (common line of switch) to an output and clear it (connect to 0 volts)
    2, Make RD4 an input, check if the button has been pressed (value=0) or if it has not been pressed (value=1), if pressed then give the variable KEY a value (1,2,3 or 4 etc).
    3, Repeat 2, above with RD5 etc.
    4, Make RC1 (common line of switch) an input and continue with the rest of your code.

    The use of control line RC1 is to stop a button press corrupting the display if it is pressed when the display is being sent data. I have never seen any corruption of the display using this system and it has proved 100% reliable.

    I use the software as a subroutine and call it just before I need a key input with the line “GOSUB button_check” and generally use the subroutine as an “include” file.

    I hope you find this useful.

    73 de Mark Rodgers G0EBB.

    Download the code HERE
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