7 segment display help

Discussion in 'The Projects Forum' started by CTRL+X, Jul 1, 2009.

  1. CTRL+X

    Thread Starter Member

    Jul 1, 2009
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    Looking for someone to start me in the right direction here.

    What I'm trying to do is design a simple 7 segment led display that is driving off of a 7 voltage differentials. I'll explain.... I am trying to make a gear indicator display for a motorcycle. There is a gear indicator on the motorcycle that for each gear position utilizes a different resistor value inline back to the ECU.

    I saw this design here. http://www.bluegauges.com/gearindicatorplans.htm

    but I would like to replace the LED's with a 7 segment that reads out the gear number.

    Does someone see a simple way to convert the schematic in the link above to do what I want.

    I'm working on it, but I'm sure someone else here could spot a better way than what I'll probably come up with.

    Thanks for any help
     
  2. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I can help you with this. It would take 6 transistors some diodes and some more resistors. You would continue to use the existing circuit minus the single LED's. The LM339 comparators would still need to be used.
    Attached is a 7 segment diagram that allows the numbers 1 and 4 to be displayed. We will use some transistors inplace of the switches.
     
  3. CTRL+X

    Thread Starter Member

    Jul 1, 2009
    26
    0
    Thanks for the reply. So basically each LED in the original circuit would be replaced by a transistor that when switched, would feed current to a certain set of LED's to create the number?

    Is there any way to do this without the LM339 comparators? Maybe using zener diodes?
     
  4. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I don't think so as the comparators are picking up a signal from the gear shift circuitry.

    The reason for the additional transistors is to drive multiple segments of the 7 segment display. My circuit showed a common anode type, but I think we will have to go with a common cathode type and the dimming won't work unless we ad some more components. The current limiting resistors for the display depend upon the display. Do you need some help in selecting a 7 segment display?
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    Here is another version. I do not see two switches?? Outputs taken from camparator as is . Display is common cathode.
     
  6. CTRL+X

    Thread Starter Member

    Jul 1, 2009
    26
    0
    The 7 segment display that I have is common cathode. I have the display, a bunch of resistors, transistors, and diodes. However I do not have any of the IC's called for in these schematics.
    I was hoping I could achieve the same result without the IC's. If not I'll have to wait till Saturday and see if Radio Shack has the necessary IC in stock.

    The following resistances are generated across the gear indicator in each gear, which is the info I am trying to use to drive this circuit.

    1st - .6k
    2nd - .8k
    3rd - 1.5k
    4th - 2.7k
    5th - 6.8k
    6th - 15k
     
    Last edited: Jul 3, 2009
  7. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I think Bernard's circuit is better. There are other digital IC's that will do the same job, as a search for the 74C10 and 74C48 wasn't very good.
    I checked digikey and mouser with no results. I would suggest the CD4023 in place of the 74C10 and the CD4543 in place of the 74C48. I'm sure pin connections would need to be changed and some resistors changed in value + some added.

    As a side note I went to Radio Shack's website and today they showed no stock of digital IC's.
     
  8. Ruptor

    Active Member

    Apr 26, 2009
    44
    0
    Hi
    I didn't think anybody used individual logic gates any more. :) Another alternative could be a PIC. Just pot down the 6 inputs and slap the 7 segment straight on the PIC outputs. A zener, resistor and cap for 5V, a small program and its done. Just a thought.
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    If you have lots of diodes we can go from 6 lines to 7 seg without IC's. Might increase R1 to something like 100k, R3 deprnds on display.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
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    If you wish to use diodes, here is one way to make a matrix to hold them. Cut 8 strips of corrigated cardboard, 3/8 in wide & 13 channels long,& glue them together. Glue on a back plate of thin cardboard & prick holes for diodes and resistors with ice pick,nail or center-punch. Put diodes in anode first & resistors. Buss lettered columns together on back, numbered columns on front. If you wish, can add another strip to hold transistors.
     
  11. CTRL+X

    Thread Starter Member

    Jul 1, 2009
    26
    0
    Took me a second to visualize how you had that laid out, but that's a great idea.

    Thanks for all the help, I'm understanding it better the more I look over the schematics. Still not sure if I'll go with the diodes, or just get some comparators, or maybe even PIC.
    I'm sorta learning as I go here.
     
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