Building a 3 Digit LED counter

Discussion in 'The Projects Forum' started by firebirdta84, Feb 24, 2013.

  1. firebirdta84

    Thread Starter New Member

    Feb 24, 2013
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    Hi everyone,

    I've had some limited exposure to circuit building and I've got a question. I need to build a 3 digit LED counter similar to this one:

    http://www.kitsrus.com/pdf/k1.pdf

    However, with this schematic, and with all others I've seen, the only way to increase the numbers is to manually press a button. I'd like this to work so that whenever power is applied, the counter automatically starts cycling up from 1-999 then starts over, exactly like this video shows:

    https://www.youtube.com/watch?v=MIvMBCN5Sg4

    Can someone point me in the right direction?

    Thanks
    Joe
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Very likely the easiest way to accomplish what you want is to buy this kit and add an external circuit to auto clock it. If you are interested in doing it that way, someone here can probably devise the add on circuitry.

    As you see in the video, there is an external circuit (lower right side of the breadboard) that is providing the clock pulses.

    Is that suitable to you?
     
    Last edited: Feb 24, 2013
  3. takao21203

    Distinguished Member

    Apr 28, 2012
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    Why do you want to build this?

    For the purpose of dealing with the wiring and LED 7seg decoding?

    Or for the purpose to actually display something? I mean will this circuit be used for something later on?

    7Seg displays are rather boring and it is a lot of effort to wire them.
    Extra components as well.

    If you have fun soldering them or plugging them into a breadboard...

    You should better use a microcontroller.

    PICKIT3 + buy any 16F you want. No extra parts needed. It is not difficult to do it in 2 hours from receiving the goods to complete circuit.

    Or STM8 discovery. Very low price, and more than enough I/O for a LED 7seg display.

    If you want an automatic counter in digital logic, you need to design a complex circuit. And it will have many wires.

    If you want to display something for a purpose, get one of my serial LED displays. https://www.youtube.com/watch?v=wX30wmR0w00

    Also 3-digit displays can be soldered to the PCB.

    All you need is power supply, and 3 wires.

    I guess maybe you want to build the circuit itself, and to learn about 7seg decoding. There is not so much interesting matter contained here.

    But I do not make choices for you.

    Also the digital logic ICs in question are expensive and some of them hard to get. Especially for HEX.

    You can for instance use a few 4bit comperators, some DIL switches as well to program the number. Then you route all their outputs to a large AND. This output in turn resets the counter.

    If you want this, look for "4 bit comperator", they do exist as 74xx or 40xx logic ICs. You need more than one.

    The circuit shown can only display one digit at a time.

    You'd need 6x 4bit comperators, and a 6-input AND.

    My opinion is that it would be of little use to build this, except it is a means of getting started with digital technology.

    The microcontroller route is far more effective.

    You do not have to use PICs.

    STM8 also are good to use.
     
  4. takao21203

    Distinguished Member

    Apr 28, 2012
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    Over the last few years a single micro-processor chip like
    the Atmel AT90S1200 can do away with all cmos IC's.
    See our Kits 129, 141, 148 and 154 for such examples.

    From the PDF.

    Yes. I did not mention Atmel. And the well known Arduino.
    Displays including 7seg are well explained on Arduino.cc (this is a forum).
     
  5. firebirdta84

    Thread Starter New Member

    Feb 24, 2013
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    I should mention that this is for a display piece, so it doesn't need to function any further than the counter from 1-999 and repeat. And it needs to use the 7 segment displays.

    I am fine with following a schematic to wire something up, but I don't have the knowledge to create something on my own, or do I know how to program chips. If I can adapt the schematic shown in the link I sent, I think that would be the best bet. Can someone assist me with that?

    Thank you!
    Joe
     
  6. takao21203

    Distinguished Member

    Apr 28, 2012
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    Such a circuit does not exist with that technology, so it is required to design and to draw it. Some hours work at least.

    Also the linked PCB kit is not particulary good for this.

    It is a serial display.

    If you want to build it from a fairly large 74xx chips schematic, it would be better to design it freshly.

    Maybe you can download WINCUPL. It is a dated software for CPLDs, but also can simulate TTL circuits (with logic gates).

    If you can find someone who wants to draw that schematic for you, that would be great.

    I know how to proceed, and I could design such a circuit, but as I see little use in such a complicate circuit, I can not invest 2 or 3 hours to draw it properly with software and test it.

    There are for instance BCD decade counters I think, they will reset/overflow automatically.

    Even so, you need 6 ICs, plus a timebase, that would be a NE555 perhaps.
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    All you need is a 555 astable circuit to clock the counter and display from kitsrus. That 555 clock circuit would replace the buttons and debouncer circuitry shown in the kitsrus instructions. Here is a schematic for a 555 astable circuit.

    [​IMG]


    You can eliminate some components from this clock circuit. You don't need SW1, R3, R4, R5, LED1, or LED2. In that case, pin 4 of the 555 should be tied to Vcc.
     
  8. takao21203

    Distinguished Member

    Apr 28, 2012
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    Easier to use this.

    The gate is an inverter.
     
  9. tracecom

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    NE555 circuit: 1 IC, 2 resistors, 3 capacitors

    Inverter circuit: 1 IC, 3 resistors, 3 capacitors
     
  10. SPQR

    Member

    Nov 4, 2011
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    I built one just like you want a couple of months ago just to learn how to connect 3 7seg LEDs and write code to count from 0-999.

    I used an Arduino, some resistors, and a 3 digit 7 seg LED set I bought on Amazon.

    I'd be happy to share it with you, code and all, but to be honest, I'd vote for you buying the kit, or using the recommendations of the experts whove already answered - much easier.
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    This is a common design exercise in any introductory course in digital logic.

    Firstly, decide if you want to use TTL (7400 series ICs) or CMOS (4000 series ICs).

    You will need a BCD counter, BCD-to-7-segment decoder/driver, 7-segment LED,
    all multiplied by the number of digits desired.

    Then you need a 555 timer circuit to clock the counters.

    Add some resistors and capacitors and that's it.

    Add a breadboard, power supply and start wiring.
     
  12. firebirdta84

    Thread Starter New Member

    Feb 24, 2013
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    Yes, I plan on purchasing the kit, just needed to know how to modify it. I will get it in my hands and start playing with it to see if I can figure out how to incorporate the 555 timer. Thanks guys - I will be in touch with questions!
     
  13. MrChips

    Moderator

    Oct 2, 2009
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    Skip the kit and build it yourself from my suggestion.
    You will learn a lot more building it yourself.
     
  14. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Just a note. It looks like the kitsrus website has been hijacked. My antivirus software is reporting the new destination as "dangerous."
     
  15. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    MrChips is correct that you will learn more by building the circuit from scratch. In addition, $23 is a little pricey for the kit.

    On the other hand, if you just want the shortest path to a completed device, the kit plus a NE555 clock looks pretty easy.

    [​IMG]


    Apparently, the buttons and debounce gates are on a separate PCB, and are connected by six wires. You could tap into that connector to pull power and ground for the NE555 circuit I posted, and to connect pin 3 of the 555 to the clock input lead for the counter.

    Of course, things that look simple don't always work out. Good luck with whichever way you decide to go.
     
  16. sheldons

    Active Member

    Oct 26, 2011
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    heres another way to drive your circuit with audio .....
     
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