7447 decoder

Discussion in 'General Electronics Chat' started by mindgame2, Nov 13, 2009.

  1. mindgame2

    Thread Starter Member

    Jan 24, 2009
    12
    0
    hi guys
    i am having certain issues connecting the decoder and the seven segment display.rest of the circuit is sorted out but could not figure it out how to use the 3,4,5, legs of the decoder
    all the legs are active low inputs
    plz reply as soon as possible:)
    [​IMG][​IMG][​IMG][​IMG]
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,142
    1,790
    Links are busted.

    Pin 3 - Lamp Test will turn all of the segments on ("active"). The diplay will look like the number "8".
    Pin 4 - RBO - Ripple Blanking Output
    Pin 5 - RBI - Ripple Blanking Input

    Ripple blanking is the process of supressing the display of leading zeros in a multi-digit display. The truth table on page 3 of the TI data sheet has the details.

    http://focus.ti.com/lit/ds/symlink/sn7447a.pdf

    Consider a three digit display. If the value to display is "56" you can display a blank followed by the digits "5" and "6" or you can display "056". It is all up to you how you want your display to look.
     
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