BCD Decoder

Discussion in 'General Electronics Chat' started by KCHARROIS, Jan 31, 2013.

  1. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
    1
    Hello,

    I'm looking into building an 8x8 matrix and would like to activate each column one at a time. The pic I'd like to use only has 20 pins and I would only like to use three pins to control the columns. Now to do this I have bcd decoder (74HC/HCT42). But this decoder turns on 7 pins and turns 1 OFF and I'd like to the opposite??? Can I use the pin that is currently OFF as ground?

    Thanks
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Do you have access to 1:8 or 1:10(decade) multiplexer ICs?

    If you are using a microcontroller, the MUX and shift register logic chips make things simple for port expansion.

    This was posted just a couple days ago The OP did an excellent job with description, write up and code. Perhaps that may help you? Continue in this thread, rather than bumping the completed projects with this question.
     
    Last edited: Jan 31, 2013
  3. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    You might consider using a 74HC238 instead. A 74HC595 might be a good candidate, as well as a 74HC164, but none of these devices can source much current.
     
  4. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
    1
    Thats the thing I was looking at the car game microcontroller from Brad but I dont understand how he used the 7442? I think the decade counter will work better.

    Thanks
     
  5. crutschow

    Expert

    Mar 14, 2008
    12,988
    3,226
    The pin can be considered as a ground but it can sink only a maximum of 4mA. For more than that you will have to add a buffer IC or transistor.
     
  6. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    He was able to use the 7442 as a sinking driver because he was driving the cathodes on his common anode row display.
     
Loading...