2LEDDisplays

Discussion in 'Homework Help' started by mpuvdd, Feb 12, 2007.

  1. mpuvdd

    Thread Starter Active Member

    Feb 11, 2007
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    I am in the process of building a rpm counter that uses IR to count the amount of transitions a color coated wheel (attached to a motor) makes. It is pretty much my first real, "made up" project and I'm having trouble w/ displaying the counter's value on two LED displays. Could anyone tell (or show) me how to drive two LED displays. I have a 7 bit BCD counter (counts to 127). Once the two displays reach 99 I want the display to freeze and then I will reset it manually. Preferably the simplest cheapest IC/setup possible. Thanks,
    mpuvdd
     
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    which counter IC? Also can you post a graphic (not the excerable word format) of the schematic you have?
     
  3. mpuvdd

    Thread Starter Active Member

    Feb 11, 2007
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    I have a TI CD4024BE counter. My schematic is to large to import onto this site but if you don't mind I could email it to you and anyone else interested.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    You might find that a pair of 4511's or 4544's would help to drive the displays. I think you might consider that a 4518 will do lots better as your counter. It gives you two BCD counters with enables and clear inputs. The 4024 is a ripple counter whose output will have to be decoded to give a BCD output. With the 4518, a couple of external NAND gates will let you freeze the count at 99.

    Generally speaking, tachometers are like frequency counters. You accumulate a count over some period of time, which is displayed as RPM. At the end of the time period, the counter is reset for the next counting cycle. That makes it continuous in operation - you don't have to push a reset button.
     
  5. mpuvdd

    Thread Starter Active Member

    Feb 11, 2007
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    All right! So I think I'm going to go w/ a 4518 and then sort of cascade the two counters within it to create a two-digit display. Then I'll AND the outputs together and tie them to the reset pin so that once each counter reaches 9, it resets. And finaly I'll AND both counters together so that they reset after they reach 99. Any suggestions on BCD to 7-seg. decoders? Thanks
    mpuvdd
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    As I said before - 4511 or 4544 BCD to 7 segment drivers.