switching multiple leds on

Discussion in 'The Projects Forum' started by rjfon1, Oct 1, 2010.

  1. rjfon1

    Thread Starter New Member

    Oct 1, 2010
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    0
    Good evening all.
    Just wondering if someone can help me here.
    I need a circuit to turn on and off different coloured leds on a single momentary switch. ie:
    starts at off
    1 push-red led lights
    another push -red off and green on
    another push -red off blue on
    another push -blue off
    the cycle starts again.
    I would like this for a small light for in an aircraft, different lamps for different purposes and locations in the aircraft.
    Any circuit ideas? I presume with transisters, and due to the low voltage (2.4-3.6V) resisters would not be required.
    MAny thanks in advance.
    Rob.
     
  2. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    I would suggest you do a search for shift registers. You could use one to switch transistors to control your LEDs. There are some great helps pages on this sites for LEDS.
     
  3. rjfon1

    Thread Starter New Member

    Oct 1, 2010
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    Thanks. I'll start checking shift registers.
    Rob.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    The idea resistors are not required if you are using low voltage is a myth. You will not have enough voltage to power the LEDs, or if you do and the power supply has any current capability they will fry. If you try to control the current using voltage they will be extremely unstable (brightly frying one second, dim the next). It is current, not voltage, that powers LEDs, and the current needs to be stable.

    Small batteries (such as watch cells) have internal resistance that replaces an external resistor. The resistor is still there though, it is just part of the battery.

    LEDs only start to conduct if you exceed their dropping voltage, after that there is no mechanism except resistors to limit current through them.

    LEDs, 555s, Flashers, and Light Chasers
     
    rjfon1 and WINPINPH1 like this.
  5. rjfon1

    Thread Starter New Member

    Oct 1, 2010
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    0
    Thanks Bill for the quick reply.
    I have a circuit tht I may modify which is a sequential switch using a 4017.
    I need four LEDs which are red, green, blue, white.
    As this is a 10 digit counter I will use Q0-Q3 for the Leds. Q4 will be routed to the reset. There is a debounce built in for the momentary switch.
    This will be running off 3x1.2V watch batteries due to the size as it will be built into an aviation headset. I will be looking for a smaller package than the DIL 'N' package, but must do a bit more research. Thanks again.
    Rob.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,142
    3,054
    . Definitely makes sense to use a counter for this, but maybe a 2,4,8,16 counter would make more sense?
     
  7. rjfon1

    Thread Starter New Member

    Oct 1, 2010
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    Wouldn't know what to use, or how they work. Would look up datasheets. Any suggestions.
    Rob.
     
  8. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    No.

    Besides being a decade counter, 4017 has decoded output which means only one its ten output pins will go high.

    With a normal binary counter, one still have to decode the binary stages so that only one output can be high at any moment to drive the various LEDs.
     
  9. WINPINPH1

    New Member

    Sep 27, 2010
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    correct me if i'm wrong.

    i think there's a 4000 series chip that's specially created for 4 output. It will lessen your wiring.

    It's up to you.
     
  10. rjfon1

    Thread Starter New Member

    Oct 1, 2010
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    At this stage I only know of the 4017. If you know the number of the four output, that'd be appreciated. I'll keep looking as well.
    Rob.
     
  11. t06afre

    AAC Fanatic!

    May 11, 2009
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    Can you use a small microcontroller?
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    If you read the link I gave you it shows how to use simple diodes with the 4017 to create an sequence you want, as long as it is 10 steps or under. It also shows you how to cascade several 4017s to create more than 10 steps.
     
  13. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    How about the 4029? It is a 4 bit counter that operates in either decimal or binary mode?
     
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