Simple IC To LED Wiring - Need Help

Discussion in 'General Electronics Chat' started by ziggy1212, Nov 4, 2010.

  1. ziggy1212

    Thread Starter New Member

    Oct 10, 2009
    I am trying to drive my 7-segment display ( LSD3221-11 ) from a 74LS47 7-segment converter. Maybe I'm missing something or simply too tired, but how do I wire up the last 4 pins (3,6,9,14).
    I know 1st I must buffer each input (A-G) with a resistor. Then,
    A-PIN 1
    The only datasheet I could find for my part is at but I'm confused on what it's telling me.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    It's telling you that you have a common anode display, and which pins attach to which segments.

    pin 3 - common anode
    pin 6 - cathode of Left Decimal Point
    pin 9 - cathode of Right Decimal Point
    pin1 14 - another connection to the common anode.
    ziggy1212 likes this.
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    Note that with a common-anode display, that you connect the power supply to the anode and the segment(s) will light when the output of the converter is low and sinking current.

    If you want the segments on when the output is high, then you either need to add inverters to the converter outputs, or get a common-cathode display where you ground the cathode and drive the segments with the converter.

    Take a look at the converter datasheet and be sure that the outputs are capable of sourcing or sinking the required current for the LED segments, especially when all segments are on. If not, then you will need to add buffers or inverters that are capable of meeting the current requirements of the display.
    ziggy1212 likes this.
  4. ziggy1212

    Thread Starter New Member

    Oct 10, 2009
    Thanks for the help. It seems the only wire I was missing was the Vcc to PIN14.