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Led Signal lamp does not flash

Discussion in 'Electronic Basics' started by steve, Sep 4, 2007.

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  1. steve

    steve Guest

    I have a friend that has a motorcycle. He has added a side car onto
    it. Because of this he has added more lamps onto his motorcycle. To
    reduce the electricity used by all the extra lamps he has replaced his
    signal lamps with led signal lamps. They are several LEDs put in a
    lamp package with socket.

    However when he signals the lamps turn on but dont flash. Im guessing
    that the flashing unit is not drawing enough power to turn off and on.

    Can anyone give me a solution to this. I have some small expereince
    with hobby electronics. Bulding and repairing basic electronic
    devices. I believe you can buy a device to fix this but thought it
    would be fun to solve it myself by building something.

  2. JeffM

    JeffM Guest

  3. The easiest (and maybe coolest) solution might be to add a lot more LEDs to
    draw about the same current as the incandescent lamp. Now those will be
    some bright blinkers! I'm not sure how much effect the inrush current of
    incandescent lamps has on the thermal blinker. Maybe you can add a
    capacitor across the LEDs?

  4. steve

    steve Guest

    The problem with this is that the whole point is to use less power, to
    save power for the added power used up by the side car lights.

    Any other ideas ??

  5. default

    default Guest

    Can you get alt.binaries.schematics.electronic ?

    I can post what I made for my bike only 2 transistors and works over a
    range of few hundred milliamps to 20 amps.
  6. steve

    steve Guest

    Yes thank you
  7. steve

    steve Guest

    Sadly I miss spoke. It looks like I cannot get to alt.binaries.

    Can you put it here with an ascii program.

  8. If default has LTSpice, I can provide a program to automatically
    convert the circuit. Or post the LTSpice ASC file and I can convert
    it and post it.

  9. JeffM

    JeffM Guest

    ISTR someone asking if you had uploaded that somewhere.
    I don't recall an answer, yay or nay.
  10. I hoped I had, if someone asked. But I do sometimes miss messages or,
    having seen them perhaps, forget to respond.

    Here's the link, in general:

    And here is the actual ZIP file with the .COM and .SYM files:

    Just place them together in the same directory and have that directory
    in your PATH variable. It's a DOS program. There is an option that
    works under the Win3.1 through WinME operating systems (and I seem to
    recall that it worked under Win2k) which copies directly to the
    clipboard. However... it doesn't appear that the method I used works
    under WinXP. So that is a pain and I need to research how to access
    the clipboard from a DOS box under WinNT.

    I may move this over to a VB program or else a VC++. I just haven't
    bothered, yet, as the tool is fine for my own use as it is and I
    haven't had anyone letting me know they use it. So no motivation, as

    The library file (ASC.SYM) that is included is easy to edit with any
    standard ascii file editor, but frankly cryptic and terse. I can
    explain it easily enough and it isn't hard to work with, if anyone has
    a mind to expand it further. (I could use help with that.) Symbols
    that are NOT found in ASC.SYM are not translated and just show up as
    "holes" in the schematic. When I'm working with schematics and find
    that I'm missing an entry, I just pop up the .SYM file and paste in a
    few ascii lines of what I'd like to see and then rerun the program.

  11. default

    default Guest

    Posted to alt.binaries.schematics.electronic

    Message-ID: <>

    Go to

    With your browser

    In the search window enter: flasher.gif

    Let me know if that works for you
  12. default

    default Guest

    Theory of Operation:

    Figure 1: Electronic Auto/Motorcycle turn signal flasher suitable for
    low current LED signal
    lamps or incandescent lamps.
    The electronic turn signal flasher works over a load range of about 20
    milliamps to 10+ amps
    (will flash a pair of standard auto headlamps)
    Theory of Operation:
    Initially, the turn signal is in an off state but provides voltage to
    the signal flasher circuit in
    series with the lamp(s). The 10 uf electrolytic capacitor begins to
    charge. When the capacitor
    voltage exceeds the base voltage by six tenths of a volt Q1 starts
    conducting and puts the
    capacitor voltage on the gate of the N channel power MOSFET Q2,
    turning on the mosfet. The
    initial conduction of the mosfet causes the base voltage on Q1 to
    drop, which, in turn, causes Q1
    to conduct harder and drive the mosfet harder . This action keeps the
    mosfet from spending time
    in its linear region, turning it on hard, minimizing power dissipation
    in the mosfet.
    The capacitor discharges through the 100 K resistor. When the voltage
    on the gate of the mosfet
    falls below its conduction threshold, its "on" resistance begins to
    rise. This causes the voltage on
    the emitter of Q1 to rise, and since the base of Q1 has dropped it
    tends to turn off quickly,
    allowing Q2 to turn off more etc., until the circuit switches back to
    its initial state turning the
    series connected turn signal lamp off.
    I don't know the part number of the mosfet but the specifications are:
    Voltage source to drain 60,
    Resistance in the "on" state is .04 ohms, maximum current 30 amps,
    TO220 package. No
    heatsink is required with up to about 15 amps or more.
    The entire circuit was mounted on 1" X 1" piece of perf board. All
    resistors 1/4 watt. I put the
    circuit in a small empty dental floss container and filled it with
    epoxy, running the wires out to a
    pair of 1/4" male "quick connects," that plug into the turn signal
    flasher connector. The on time
    and off time can be adjusted independently by changing the value of
    the 220K charging resistor
    (off) or 100K discharge resistor (on), or changing the value of the
    capacitor (both off and on).
  13. steve

    steve Guest

    Yes that did work thank you.

    I will take a look at it and see how it works.

    thanks again.
  14. default

    default Guest


    I tried a lot of alternatives before I hit on this one.

    First was a trip to the auto parts store - they wanted 8.99 USD for it
    and through the smoked cover I could see one three terminal device,
    large cap and a RELAY.

    With my immense ego - I figured with a six pack of good beer and some
    quality time tinkering I could do it with the parts from my junk
    drawer (room).

    I designed four turn signal flashers when I got back home and went
    through a case of beer. first off was a 555 timer working a relay
    then mosfet, then an Eccles Jordan multivibrator driving a 600 ohm
    relay and switching 8 amps max, and a flashing red 5V led switching an
    NPN bipolar - all required a rather large cap to hold up the supply
    voltage while the silly thing shorted its own power supply.

    Finally I hit on the mosfet. Q1 is a little unconventional with the
    bias - but since there isn't any significant current requirement for
    mosfets it works fine (fact is if you leave out the gate discharge
    resistor (100K) it takes too long to discharge the 10 uf cap)

    All told a very nice day tinkering and drinking good beer - and I
    guess it finally cost me ~15 USD to replace the $9 store bought
    flasher - but mine has no contacts to wear out or relay armature to
    adjust and I got a day's entertainment doing what I love.

    In balance, an excellent day. Vivaldi on the stereo, good beer, quiet
    time. Life isn't about electronics after all.

    The 3.2 V zener can be replaced with a series string of 5 forward
    biased signal or rectifier diodes. or a couple of fwd biased LEDs.

    You might even use a power NPN transistor in place of the mosfet but
    the 10 uf cap might have to be larger and the 100 K would be
    unnecessary. Just a thought - haven't tried it but it should
    oscillate (fast).

    This thing has been in my motorcycle for two years now and works
  15. By the way, here is what the program I have generates from one version
    I drew up in LTSpice:
    That's all automatic. Mosfet looks a little 'flat' I suppose. But
    that's the size it has to have in ascii to fit with the space
    allotments made by LTSpice.

  16. hmm. Wouldn't that be a little difficult going through the diode,
    though? I can see a path through the emitter of the bjt and via the
    220k which may have it's other end pinched down. But wouldn't it help
    to add a parallel diode so that there is a nice path via the 100k?

  17. ....parallel reversed diode, in case it is not clear from context...
  18. Of course, now that I'm thinking about that... why not just remove the
    diode? I forgot that it shows up only along one branch from the
    supply and had imagined earlier that it was there to be a protection
    against reversal. But I think your description is fine, just that the
    diode may not be required. Why did you add it?

  19. default

    default Guest

    The cap is discharging while the mosfet is in the conducting state
    (shorting its power source). Q one's bias is "on," with its base
    close to zero and emitter positive. Resistor is also discharging the
    gate of the mosfet's capacitance.

    The signal diode is there to remove the discharge path through the
    shorted power source - the objective isn't to discharge the cap
    rapidly - that's what is holding the gate of the mosfet up and keeping
    the signal lamp on.
  20. default

    default Guest

    The diode isn't "necessary" but is slows the discharge of the cap and
    decreases the size cap required.
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