Rolling Display using 3 seven segment displays

Discussion in 'General Electronics Chat' started by rishirajsurti, Mar 15, 2014.

  1. rishirajsurti

    Thread Starter New Member

    Mar 15, 2014
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    Hi guys!
    I am doing a project in which I have to make a rolling display using 3 seven segment displays.
    The displays should roll the number "789".
    (as in 789-> 978-> 897-> 789)
    I am stuck.
    Can anyone please give me some ideas?

    P.S. What is your opinion about ic 4017? It's too complicated, I think. Do you have a simpler method?

    Thanks:)
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Since you are not counting anything you can just set values to represent the segments of 7, 8 and 9. Then use a Shift register to rotate the values from one LED to the next and then rotate. Look up "shift register"

    I am guessing you can use an 8-bit DIP switch to seed the initial value (7), shift it into a shift register that drives the third LED. Then adjust the dIP switches for an 8, then **** it into the third LED position, and the 7 will cascade into the 2nd LED position and then repeat for the 9. Once all three digits are shifted into place, then activate a switch to make the three shift register chips form a closed loop (while disconnecting from the dIP switch.

    Good luck - I am not even going to ask why this could be necessary.
     
  3. panic mode

    Senior Member

    Oct 10, 2011
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    you could use 555 and 4017 (or whatever you like) to produce rolling sequence and ULN2703 or ULN2803 (or transistor stage) as a buffer.

    your common anode 7-segment displays will need own series resistor (for each segment). to turn any of them on, connect common anode to +V and other side of resistor to GND . use this to turn segments on that are always on (any of three display will allways show either 7,8,9 - this means that segments 'a', 'b', 'c' are always on).

    connect the rest to outputs of ULN instead of GND. to prevent backfeeding (and weak glow of segments when not active), also insert diode between resistor and ULN.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    A 4017 gives decoded decimal outputs and would not readily work for your needs.

    You could use a CD4035 4-bit parallel in/out shift register, one for each digit. You would parallel load binary 7,8,9 (hard-wire or DIP switch inputs) into the 3 shift registers connected in series loop. Then clock them 4 times and pause, to transfer to the next digit giving 987. Repeat 4 times for the last transfer to give 897. Then restart the load sequence back to 789 (or just keep shifting).

    The parallel outputs of the shift register could go to a BCD (Binary Coded Decimal) to 7-segment display converter such as a CD4056.
     
  5. #12

    Expert

    Nov 30, 2010
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    As usual, there are a dozen ways to do this. I'm wondering why a microprocessor guy hasn't chimed in. Seems about equal in time required to design and build it, either way.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That'd be too easy.:p
    Max.
     
    panic mode and #12 like this.
  7. crutschow

    Expert

    Mar 14, 2008
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    As noted, a microprocessor would likely be the easiest way to do if, if you have the expertise to do the programming.
     
  8. panic mode

    Senior Member

    Oct 10, 2011
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  9. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    I was too busy explaining Mesh Current Method.
    ☺7
     
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