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Repeating circuit: 1, 2, 3, 1, 2, 3...

Discussion in 'Electronic Basics' started by Don Gilmore, Dec 8, 2012.

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  1. Don Gilmore

    Don Gilmore Guest


    I'm an ME working on a small project where I'd like to do something ridiculously simple, yet I keep coming up with complex solutions. There is probably a simple way to do this that I am missing.

    What I'd like to do is cycle between three outputs--let's say three discrete LED's--in a continuous circle using a square wave clock input. If the LED's are numbered 1, 2 and 3, I want them to cycle 123123123123... The inputwould be the square wave from a function generator and I'd like to controlthe speed of the LED's by the frequency.

    I keep coming up with complicated ideas like using a counter that outputs to a decoder. Surely there is an easier way?

    Kansas City
  2. Don Gilmore

    Don Gilmore Guest

    A 4017 decoded decade counter, connected to reset at three. If the

    I thought about a 4017, but didn't know that I could reset it at three. How is this done? Would I connect output 3 to the reset line? It is important that each output gets equal pauses or skipped pulses.

  3. Connect Q4 to MR and the counter resets immediately after the 3rd pulse. So
    you will have a short pause in the ns area between pulse 3 and puls 1. You
    may need to lengthen it somewhat if the Q4 does not fully reset the counter.
    A diode and an RC will do that trick.

    An alternative is a synchronous serial in parallel out shift register. "NOR"
    the first and the second output and feed back to the serial input.

    petrus bitbyter
  4. whit3rd

    whit3rd Guest

    I'm not sure why a function generator is useful, but if you have one,
    set it to a ramp waveform (sawtooth) and use a bargraph display
    chip (LM3914 or somesuch). One chip and the LEDs, and you're done.

    Decoded counters (CD4017 in CMOS, SN74142 in TTL) are also available in a single
    chip, you just need to worry about reset setup and hold times when you truncate
    their sequence.
  5. ehsjr

    ehsjr Guest

    And it appears you're under thinking it. The op wants to control
    the leds with an external generator:
    "The input would be the square wave from a function generator and
    I'd like to control the speed of the LED's by the frequency."

    I don't see where you or David has addressed that with the picaxe
    idea in any of the posts in this thread.

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