using a 7448 decoder and 7 segment cathode

Discussion in 'The Projects Forum' started by cjjg, Oct 5, 2008.

  1. cjjg

    Thread Starter New Member

    Oct 5, 2008
    2
    0
    guyz, i rily had a hard tym on this... can u please help me...
    i need to construct a circuit using 7448 decoder and a 7 segment cathode...
    the situation goes like this.....

    \=> if 0,7,4,2,5 is switched on, the 7 segment cathode will display those numbers... otherwise it's off (it won't display anything) but.....
    if numbers 10,11,12 is switched on, it will display 0(zero) and
    if numbers 13,14,15 is on, it will display 8(eight).....

    i badly need ur help!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Sounds like you have your ABCD inputs scrambled in with the RBI (ripple blanking input)
    A is the LSB of the digit.
    D is the MSB of the digit.
    Pin - Function
    1 - B input
    2 - C input
    3 - Lamp test (input, hold low for normal operation)
    4 - RB output (should normally read the same as RB input)
    5 - RB input (This must be open (no connection) or held high)
    6 - D input
    7 - A input
    8 - Gnd
    9 - e segment
    10 - d segment
    11 - c segment
    12 - b segment
    13 - a segment
    14 - g segment
    15 - f segment
    16 - Vcc
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Wire the 7848 with the display as you would if you wanted to display all the numbers. Finally, use combinations with AND gates to control the LT pin (lamp test) and zero blanking control (RBI) to turn on all the leds or turn them all off at the desired numbers. The AND gates will take signal from the output of the counter or whatever drives the four inputs of the 7848. Read the datasheet for the 7848 pin configuration.
     
  4. cjjg

    Thread Starter New Member

    Oct 5, 2008
    2
    0
    thanks a lot!
     
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