push buttons and 7 segment displays

Discussion in 'General Electronics Chat' started by hunterage2000, Nov 5, 2012.

  1. hunterage2000

    Thread Starter Active Member

    May 2, 2010
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    Say if you have 10 push buttons connected to a seven segment display and each button is used to display 0-9, How would this be setup?

    I tried with 2 buttons first for 0(1111110) and 1(0110000) but for each button it displays the combined digits to show 0.

    I know how this is done through a microcontroller but Im not sure how I can do this without. Can the seperate combinations be somehow seperated fromeach other and still be displayed on the same display?
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
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    You could do this with diodes. Each button would have diodes connected to the relevant LED segments. Will only work if you press one button at a time. Will need quite a lot of diodes!
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    Or one 74147 type chip, a BCD to seven segment decoder, and probably some 7404 ICs also
     
    Last edited: Nov 5, 2012
  4. takao21203

    Distinguished Member

    Apr 28, 2012
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    These decoder chips were difficult to buy in the early 2000s already.
    I wasn't able to get HEX decoders through my local shop, and they also did not find any in their suppliers catalogues. They did not have internet already at this time.

    You can do all the decoding work for a 4 digit display with a small inexpensive microcontroller.

    For simple tasks like that you don't need an expensive evalution board. Simply buy some blank chips, and a FLASH writer. They are even easier to use than 74xx logic / decoders.

    Or you could use GAL chips- however FLASH writers for these aren't so cheap, and software can be difficult to set up.

    If you fancy, you could use a small 2716 EPROM. You'd use the pushbuttons as the address input! It could be interesting for a student, but normally microcontrollers are used for LED/pushbutton circuits.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    You can easy get them(74xx148) at digikey in both LS and HC variant. My component vendor do also have them.
     
    Last edited: Nov 5, 2012
  7. takao21203

    Distinguished Member

    Apr 28, 2012
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    How would you drive a LED display using a 3 to 8 priority decoder?
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    Good question. I used a combined datasheet for 74xx147/74xx148. And swapped the two of them. So the correct here is to use one 74xx147. Then the output of the 74xx147 should be connected to a BCD to 7 segment decoder using 4 inverters
     
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