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Thread: Need a led blinker circuit for 12V or 3V any diagrams?

  1. #1
    Flashaholic* AlexGT's Avatar
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    Help Need a led blinker circuit for 12V or 3V any diagrams?

    Hi all!

    I am looking to get a flasher / blinker for 1 led but the electronics stores don't seem to have any, I want one to power 1 led at about 10-15 ma I want it to blink on for about 1/2 to 1 second then off for 5 seconds. The power supply can be either 3 volts or 12 volts doesn't matter.

    I've looked for schematics to build one myself if the cost is not high but haven't found any that would do this, do you know any link with a diagram with part numbers?

    Or if someone has an Energizer "Find me" flashlight and are willing to sell me the flashing led circuit let me know.

    Thanks!
    AlexGT

  2. #2
    *Flashaholic* Mr Happy's Avatar
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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    An astable multivibrator? It's very low tech but easy to build and can be made to do any timings you wish. Or use a timer IC like the 555 or a more modern equivalent?

    What about power consumption? If you want it to use the lowest possible power you will probably need something based on CMOS logic. I think there are CMOS timer chips that have very low operating currents.
    Last edited by Mr Happy; 04-25-2009 at 02:35 PM.

  3. #3
    Flashaholic* AlexGT's Avatar
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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    Yes I would like something with a very low power consumption, but I don't mind replacing 2 AA batteries every 6 months or so.

  4. #4
    Flashaholic* AlexGT's Avatar
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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    I found this circuit, looks easy to build,



    To calculate the frequency use the formula
    FHz = 1/(0.693 x (R1+(2 x R2)) x C)

    To calculate the on time use the formula:
    Tsec = 0.693 x (R1+R2) x C

    To calculate the off time use the formula:
    Tsec = 0.693 x R2 x C


    So in plain english, what resistor and capacitor I need to have the circuit do 1 second on time and 5 second off time? does this circuit work with 3 volts? 12v?

    Thanks!
    AlexGT

  5. #5
    *Flashaholic* Mr Happy's Avatar
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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    The LM555 has a minimum supply voltage of 4.5, so it won't run off 3 V successfully, but it will work fine at 12 V. It is also not a low current device, drawing a few mA in operation; mind you, if you are driving an LED at 10 to 15 mA your whole circuit is already demanding a few mA just for the flashing LED.

    Suppose you had an average current drain of 10 mA and a 2000 mAh battery, your run time would be 200 hours, or 1 week. If you drove the LED at 5 mA with a 20% duty cycle and discounted the timer circuit you would have a 1 mA load and that would give you 2000 hours, or 2-3 months.

    I'd say that if you are particularly concerned about long run times you will want a circuit that draws only microamps. There is a CMOS version of the 555, the LMC555 that will run off a 3 V power supply and meets the low power consumption requirement.

    Here's a link to the data sheet:

    http://www.national.com/ds/LM/LMC555.pdf

  6. #6
    Flashaholic* AlexGT's Avatar
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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    Hi Mr Happy

    I was able to get an energizer "Find me" flashlight on clearance at target for $3 and used the circuit it had, works great! I won't be needing to make the circuit myself.

    Thank you for your help

    AlexGT

  7. #7

    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    A PICAXE 08M with a resistor, an led and and small program (found in the manual 3) will do the job.

    Professor Anderson sells those in the USA. There you can also find som examples.

  8. #8
    *Flashaholic* Burgess's Avatar
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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    Does RadioShack still carry the National Semiconductor LM3909 ?


    This little IC will run for a year or more, on 1 AA alkaline cell.


    Very easy to do. Heck, even *I* was able to make those work.




    _

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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    Whoww, you mention the LM3909! This one has been discontinued YEEEAARS ago
    I think the schematics was in my electronics yearbook of 1980....


    Timmo.

  10. #10
    Flashaholic* abvidledUK's Avatar
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    Default Re: Need a led blinker circuit for 12V or 3V any diagrams?

    You can buy LED's with the blinking built in.

    Not too expensive either.
    Batteries, batteries, I need more batteries ........

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