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7 seg LED display schematic needed

Discussion in 'Electronic Basics' started by Baronvonrex420, Sep 26, 2003.

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  1. I searched the Web for days.......... to no avail.

    What I need is a simple schematic for a seven segment display driver that
    increments with the push of a button. Up or down, don't matter. I'm a novice
    hobbyist so go easy.

    My goal is to have 4 digits where each are incremented by it's own momentary
    contact switch. Any "stock" schematics for such a device? I could use 1 and
    duplicate it 4 times.

    In the end, I want to drive a large LED array from the output of the small
    circuit, so any help with Triacs, transistors and such would be helpful. The 7
    segment array is made up of 6 leds per segment ran at 3 in series, 2 parallel
    for a total of 42 per digit. This device will be ran at 12v DC.

    Thanks in advance!

    Greg
     
  2. cirip

    cirip Guest

    Hi,

    I suggest you take a look at 2 circuits: CD4543 and CD40192.

    Cirip
     
  3. cirip

    cirip Guest

    Also try CD4511

    Cirip
     

  4. You need

    1) A way to 'debounce' the button, so it doesn't count 100 times every time
    you push it.

    2) A counter chip that count up to the maximum number. In your case, a BCD
    counter is perfect (they sometimes come in dual counter packages, so you can
    probably get away with two counter chips for your 4 displays.)

    3) Driver chips for the 7segment display, which take the BCD output and
    convert it to drive those 7 segment displays. Unfortunately, since you are
    using these huge displays, you may not be able to use stock 7segment driver
    chips, but may have to use a power driver chip too. Look at the nte2023,
    which I haven't used, but which might be able to drive your LED arrays.

    4) A power supply (which you may already have) Some of the TTL chips will
    only run at 5V, so you might want to use CMOS chips (in the 4000 group)
    instead, which will usually run on 12V. You can get data sheets on these by
    looking on the manufacturer's web sites. Philips is a good source for
    datasheets and information.

    You can find circuits for these by googling around. You really just hook
    them up together, debounce circuit output to clock input on the counter,
    counter BCD output to input of the 7segment display chip, output of this
    chip to the driver chips, output of those to the 7 segment displays, paying
    attention to the proper polarity. Make sure that all unused inputs are
    connected to ground.

    Debounce circuits are pretty simple, generally relying on a simple RC
    scheme. Here is a reference:

    http://www.all-electric.com/schematic/debounce.htm

    Build it a step at a time, making sure that each stage does what you think
    it should before going on to the next one. I've found that prototyping with
    a solderless breadboard is a good way to ensure that things are working
    before committing the design to solder. You can debug it with a multimeter,
    I'm guessing.

    Regards, and good luck
    Bob Monsen
     
  5. Byron A Jeff

    Byron A Jeff Guest

    -I searched the Web for days.......... to no avail.

    Hmmm. Took me less than two minutes. The power of experience I guess.

    -
    -What I need is a simple schematic for a seven segment display driver that
    -increments with the push of a button. Up or down, don't matter. I'm a novice
    -hobbyist so go easy.
    -
    -My goal is to have 4 digits where each are incremented by it's own momentary
    -contact switch. Any "stock" schematics for such a device? I could use 1 and
    -duplicate it 4 times.
    -
    -In the end, I want to drive a large LED array from the output of the small
    -circuit, so any help with Triacs, transistors and such would be helpful. The 7
    -segment array is made up of 6 leds per segment ran at 3 in series, 2 parallel
    -for a total of 42 per digit. This device will be ran at 12v DC.

    Here my advice on the subject: Learn how to use microcontrollers. Here's why:
    you can leverage what you learn about microcontrollers over nearly every
    project you'll ever build. Projects such as the one list above almost always
    get "Feeping Creaturitis (FC)" ;-) where some additional piece of
    functionality is wanted or in some cases actually needed.

    The problem with building with what I call fixed programmed parts is that they
    don't handle FC very well and you end up having to search for new hardware
    in order to fill the need. You give a perfect example of this above. You'll
    need button debouncing and some method for expanding your project.

    BTW I see that it pretty much looks like a scoreboard display. FC is definitely
    enter the equation because eventually you'll want features that are related to
    the display, such as two digit counting, zeroing, blanking possibly, and the
    like. If you do what I call "programming in hardware" it'll take a bunch of
    additional hardware to facilitate adding those features. However if you use
    what I call a "jellybean microcontroller" at the core, the hardware stabilizes
    pretty quickly and you change software to keep up with FC.

    Given that, then what to use. Lots of folks use Pics, lots use AVR. Both have
    inexpensive parts, simple homebuildable programmers,and both low and high
    level programming languages to operate in. For example if I were doing this
    project I'd probably pick a PIC 16F877, use my Trivial LVP (TLVP) programmer
    which can be built in an afternoon using RatShack parts, and program probably
    in JAL, because it already has a 7 segment dsplay library.

    Microchip is sampling their parts. You can get up to 15 parts (3x5 different
    parts) every 90 days. Go to Microchip.com and click on the Sample Microchip
    icon. I would recommend getting a part in each size (8, 18,28,40 pins) and one
    from each family (12F, 16F, 18F). Note you can't do it in a single session as
    you can only get 5 different parts each time.

    I know it'll take some time to get together. But the continuing benefits you
    get from the initial investment is well worth it.

    Now on to the LED display. First a question: I presume that the two parallel
    strands are tied together? That's not a great situation because there is no
    guarantee that the two strands will draw an equal amount of current. If it
    is possible to separate those two strands and tie a separate resistor to each
    at the top, finally tying the top ends of the resistor together, that would
    be ideal.

    Also you'll need to look at the concept of multiplexing the display. When you
    multiplex instead of driving all the displays at the same time, you drive
    one at a time. That allows you to reduce the amount of hardware required to
    drive the display.

    Hope this gives you some insight. If you want to see some of the tools that I'm
    talking about check out my TLVP page here: http://www.finitesite.com/d3jsys

    BAJ
     
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