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LED Turn signals

Discussion in 'LEDs and Optoelectronics' started by altontoth, Jul 31, 2011.

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  1. altontoth

    altontoth

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    Jul 31, 2011
    I picked up some led strip lighting the other day (2 1.5' amber strips), and I want to add it to a little Yamaha scooter that I have, to increase visibility. What I want to do is have a strip on either side of the seat wired into the tail lights, but also setup so that when I turn on the turn signals, the corresponding side blinks.

    What I figured out would be to use a PNP transistor with the emitter tied to the 12V (tail light) wire, the collector running to the LED strips (and then ground), and the base having two resistors tied to it; a small resistor going to 12V (turn signal), and a larger resistor going to ground. The only problem is that any combo of resistors I can come up with either only dims from 100% to 80% for blinking, or else only illuminates the strips to about 70% brightness.

    Any thoughts? I've contemplating just shelling out for a couple of 12V solid state relays and hooking them up, but I'm sure I can make this work. Before anyone wants to bug me about modifying electrical systems on a vehicle 1) it's a scooter, so hand signals are quite readily available should something die on me, and 2) I'm not cutting any of the wires in the harness, just stripping a little bit of insulation and doing some t-splices with my wires.
     
  2. nepow

    nepow

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    1
    Jul 18, 2011
    You will have to check what regulations apply for controlling the flash duration and timming before putting any type of circuit together. This can be tricky unless you have some electronics experience. Otherwise can be simply achieved with either a timer chip or micro controller.
     
  3. daddles

    daddles

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    Jun 10, 2011
    You might also want to read the lighting regulations for where you live. Many places have rather strict requirements for automotive lighting and you might be setting yourself up for a ticket and having to remove your work.
     
  4. TBennettcc

    TBennettcc

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    Dec 4, 2010
  5. altontoth

    altontoth

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    Jul 31, 2011
    Naw, I know that this would take approximately 6 and a half seconds with a microcontroller. However, I want to use the turn signal blinker as a signal wire. The idea is that they are on regularly, and go off when the turn signal wire goes hi (so they blink, but 'opposite' to the front and rear turn signals...when they're on, the strip is off, vice-versa). As for legalities around here (Vancouver BC), there's another guy using LED lighting strips on his scooter (same scooter, same strips and location, but on all the time), and he hasn't run into any issues with the cops. The position on the scooter where I want these to go they have to be amber, which they are.

    Reasoning for choosing PNP? It seemed to make sense in my head? Despite tinkering with electronics for 15 years (I'm 25), and having done some electronics work in my electrical schooling, transistors have NEVER made much sense to me in terms of calculating values. I screwed them up in school, and unless I'm following a schematic, I usually screw them up in my hobbies too. It's part of why I was considering just getting a couple of 12V relays, and using the NC contacts, with the coil tied on to the signal flasher wire. Same effect, no hassles of building a circuit. Thoughts?
     
  6. TBennettcc

    TBennettcc

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    2
    Dec 4, 2010
    Damn. I'm about to turn 25, and I'm just getting started in electronics. Kudos to you for being able to get started so early.

    If my understanding is correct about PNP transistors, they need the base pulled lower than the emitter in order to conduct, while an NPN needs the base pulled higher than the emitter in order to conduct.

    Does your PNP transistor get hot at all while you're testing this out? Which part number is your PNP transistor?

    For additional ideas, see:

    The inverter at the bottom of the page:

    http://www.kpsec.freeuk.com/trancirc.htm#inverter

    And the PNP in the middle of the same page:

    http://www.kpsec.freeuk.com/trancirc.htm#pnp

    My guess is that you could hook up the base of the inverter to the turn signal wire, and the V+ to your +12V. Then, you hook up the inverted output from the inverter to the base of the PNP. That should give you what you're looking for. At first I was thinking that you might just be able to use the PNP circuit by itself, and tie the base of the PNP to the +12V with a resistor, but I think that the turn signal wire might just be disconnected from +12V, as opposed to switched all the way over to ground. If that's the case, I don't believe it would complete the circuit, and therefore not work.

    Good luck. I'd be interested to know what you find.
     
  7. poor mystic

    poor mystic

    1,068
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    Apr 8, 2011
    So what don't you like about the turn signal flashers they sell for automobile use? They'd do fine, surely?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,490
    2,832
    Jan 21, 2010
    I recall some time ago, someone was asking a cery similar question in regards to lights on a car that they wanted to be normally on, but flash in time with the indicators.

    It might be worth searching for that because (if I recall correctly) we came up with a working solution.

    I'll have a search too and see what I can find.

    edit: Check here.
     
    Last edited: Aug 2, 2011
  9. BobK

    BobK

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    1,688
    Jan 5, 2010
    I you are trying to get it blink from 100% to 50%, you could do it like this.

    Calculate the resistor needed 1/2 the max current.

    Use two of these in parallel, (which gives you full brightness), but in series with one of them, insert a transistor switch such that it is normally on and gos off when the blinker gows low.

    Hope this helps.

    Bob
     
  10. altontoth

    altontoth

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    Jul 31, 2011
    The scooter only contains a single flasher module ahead of the switch. If I were to rig something up, I'd likely have to change out the turn switch (which is a back and forth slider, not an arm like in a car), and who knows what else. Otherwise, I wasn't aware that you could get a signal flasher with a NC contact on it.

    That's correct. However, leaving the transistor base floating doesn't work (it needs to be pulled to ground to conduct properly). I'm using the TIP32C due to availability and current capacity. It'll handle up to 4A (or -4, depending on how you want to look at it), so no problems with me and my 0.45A. The idea is that this will likely be sealed to prevent corrosion, so it's not going to get a lot of cooling.

    Steve: Yup, using the relays was pretty much my fallback option. I'll probably just pick up a couple on my way home from work tomorrow (since I scoot right past two electronics parts suppliers :-D )

    By the way, the inspiration for this project came from here. His side lights are on steady. The only difference for me is to make them blink with the turn signals (I suppose now I'm looking at a NC contact on a relay for each side, with the coil wired into the turn signal line?)
     
    Last edited: Aug 3, 2011
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If the LEDs require a fairly low current then you may be able to do without the relay and drive them directly from the transistor.
     
  12. altontoth

    altontoth

    5
    0
    Jul 31, 2011
    That's what I was trying to do in the first place. I want them on all the time (with the tail lights), and to blink the appropriate side when the turn signal is activated (really, the way it works out, is that when the signal is lit, the LED strip is off). Each strip draws 0.45A. As I mentioned, I can get them to go from about 75% brightness to off, or from 100% to about 80%, but I haven't figured out why I can't get them to go all the way off from full brightness, which is why I'm contemplating just going the relay route.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,490
    2,832
    Jan 21, 2010
    Check out that circuit it may do what you want in the other thread. place the LED strip where the relay coil is and use a transistor that can switch the appropriate amount of current.
     
  14. altontoth

    altontoth

    5
    0
    Jul 31, 2011
    Got it working. Scrapped the solid state components. Couple of 12V automotive relays and some crimps later, got them wired up and working first try. I've uploaded a video and a couple pictures for anyone who's curious. Thanks for the suggestions!

    [​IMG]
    What a rats nest hey?

    [​IMG]
    Close-up of the relays, all wired up and ready to stuff into the scooter.

    [​IMG]
    Perfect amount of space inside the right fender to slip everything in there.

    [​IMG]
    LED strip installed on one side. Self-adhesive backing, so simply peel and stick.

    [​IMG]
    Under seat shot of the LED strip lit up.
     
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