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Make 12v LEDs blink once every 3 seconds?

Discussion in 'LEDs and Optoelectronics' started by supak111, May 4, 2013.

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  1. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

    Apr 29, 2012
    Hey everyone I'm trying to make 12v LEDs on my motorcycle blink once every 3 seconds, what would be the bast easiest way to make this work?

    I was thinking about using a turn signal flasher but that blinks every second or faster with LEDs so I need something else or modify the signal flasher.

    Another problem is the flasher uses to much electricity, I would rather try something different so the battery drain is as little as possible, the idea is to let the 15, 5mm blue LEDs I have on the motorcycle blink when the bike is parked and since LEDs don't use much power it wouldn't be a problem even if the bike isn't started for days.
  2. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

    Apr 29, 2012
    i found this:


    I don't get what the transistors BASE is connected to??
    Last edited by a moderator: May 4, 2013
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010

    In this circuit the base is not connected to anything. It seems to rely on the transistor acting like a zener diode.

    I'd love to see where you found it.

    I wouldn't connect a transistor up like this and I also wouldn't expect it to work (based on my tests of reverse biased base-emitter junctions) but I've not tested breakdown across the emitter-collector in the reverse direction.

    There are special transistors designed to do what this seems to be trying to do (PUT) and I'd probably go there.

    Either that or just get a LED with an inbuilt flashing chip.
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    OK, I just tried a 0.2mA current source in series with a 2N2222 and across the EC you get a zener action as expected. So I can't see how it could flash.

    OK, my 2N2222 has already been punished by reverse current in the BE junction, but not to the extent that would happen in this circuit.
  5. CocaCola


    Apr 7, 2012
    Psst... There is a small hint to it's origins in the Copyright tag... :p

    Back to the original question, use a flip flop circuit and omit the LEDs on the side you adjust to 3 seconds... This will give a more analog on/off

    if you want a more sharp digital on/off I would use a decade counter, clocked by a 555 just because it's easy and common parts...

    Example set the clock in to 1 second

    Output 1 = LED
    Output 2 = NC
    Output 3 = NC
    Output 4 = RESET

    I'm sure others will suggest others things, as I know there are many other ways, but in my world I just grab a PIC and write a few lines of code :)
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Bwahahahhaha. I'll swear that wasn't there before! :D
  7. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

    Apr 29, 2012
    haha yea I think I just googled "simple LED flasher circuit" and looked for literally the simplest circuit I could find in google images

    So this cirucit wouldn't work then? I found some easy 555 timer circuits but I'm still feeling like 555 timer is bit complicated for a simple job I need done here.

    PS there are a few videos of the circuit pictured above working on youtube. Adding a larger cap increases the time between flashes just not sure if it would make it somewhere between 2-4sec internals

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    Steve, it's no wonder that you missed it. Hiding something in plain sight (in bold print) is sneaky!!

    It might make you feel better to know that I didn't see it either. :D

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