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Astable 555 for Turn Signal Flasher?

Discussion in 'General Electronics Discussion' started by sall, Jan 12, 2011.

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  1. sall

    sall

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    Jan 29, 2010
    As I am in the process of finishing up LED exterior lighting on my vehicle I realize I need replace the factory turn signal flasher with a no load adjustable electronic flasher. These are available to the tune of $30 on up. Needing to order some parts anyways and it is more fun to do it yourself, so now is the right time to think about.

    Can I use a 555 timer in astable mode for this replacing R1 and R2 with pots?

    [​IMG]

    Then take the output to trigger a relay with a diode across the coil.
     
    Last edited: Jan 13, 2011
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,389
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    Jan 21, 2010
    If you want a duty cycle close to 50% then r2 will need to be significantly greater than R1. Note that there is a minimum value that R1 can be

    Also the first flash will be somewhat longer than the rest.
     
  3. sall

    sall

    51
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    Jan 29, 2010
    Yes, I just breadboarded and decided on ~53 duty cycle after reading some datasheets for auto flashers. I started out with R1 as 1k ohm and R2 as 10k ohm with a 100uF cap. Then realized needed to bypass R2 with a diode to get the duty cycle below 55%.

    I seem to be pretty happy with result. I was concerned about the first flash being delayed. I don't have an accurate way to time it but the delayed flash seems to mimic the on cycle so it looks fairly natural. I may throw in a pot but I think I have decided once I complete the sequential stuff, I may move on to using a PICAXE for controller. I would like to add an update to the vehicle and have the 3/4 flashes for lane changing when just movving the turn signal stalk to respective permission. That's a whole other learning experience there I suppose.

    Out of curiosity how could I find out or does anyone know the delay time of the first flash using this circuit?


    Also, my next question concerning this is what kind of relay should I use to have the 555 output trigger?
     
    Last edited: Jan 26, 2011
  4. janagyjr

    janagyjr

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    Dec 17, 2010
  5. sall

    sall

    51
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    Jan 29, 2010
    Yes, I came across your thread a few days ago and gave it a look over. Similar to what I am doing in a sense.

    I suppose I could also use the 555 output to trigger a transistor such as as a TIP3055?

    [​IMG]

    I would for this to be efficient as possible I also dislike the noisy factory turn signal flashers. So, the quieter the better. The TIP3055 would probably need heat sinking though, eh?

    Would there be any advantages of using a transistor over a mechanical relay. If anyone could recommend a relay with a socket I can solder to my PCB that would be great. This would make the relay on the flasher circuit replaceable which would be a huge advantage. I however am having a difficult time locating suitable.

    The factory turn signal circuit with filaments is 15A, I won't be pushing close to that. I won't never for certain however until I completely finished.
     
    Last edited: Jan 27, 2011
  6. janagyjr

    janagyjr

    67
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    Dec 17, 2010
    Yeah, I think using a heatsink on the TIP3055 would be good, but I think that's overkill.

    I wouldn't use the 555 to drive the TIP3055. The output on a 555 can source or sink ONLY 200mA max. I don't see why you'd need such a big puppy, though. I'm just using a 3904 to drive the flashing circuit. You don't need a lot of current for LEDs. My turn signal for the bicycle is going to be plenty bright enough with just six LEDs for each bank, I can't imagine needing more than 12 at most (keep the LEDs in their rows as is, the 3904 can handle 80mA) for a car (and even then you might be blinding someone with these things).

    Just some things to think about.
     
  7. sall

    sall

    51
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    Jan 29, 2010
    The point in using the TIP3055 or another lower Amperage transistor would be to increase the output of the 555 itself. Its either use transistor to do this or use the 555 output to trigger a relay.

    I won't be blinding anyone. I'm running about 300 LEDs in series of 3 or 4 at 58mA on the turn signal circuit. Max is 70mA for these LEDs. Tail lamps are PWM'd to desired brightness for running lights and brake lights.

    Thinking I'll go with something along the lines of 5A using a BD679 or similar. I do like the idea of having the relay triggered by the 555 output. If I could find a micro relay suitable that has a PCB socket would be great. This way the relay is replaceable without desoldering.

    So, what is more efficient using a transistor or using a relay? This circuit needs to be reliable and have longevity. Here is how the circuit is working as of now with TIP3055 which could be reduced.

    [​IMG]

    Any suggestion on flash rate adjustment or anything as well as the relay versus transistor for increasing the 555 output?
     
    Last edited: Jan 27, 2011
  8. janagyjr

    janagyjr

    67
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    Dec 17, 2010
    If you're max current is only 58mA for each LED, you'll only need a 2N3904 for sure.

    300?! Why so many?

    Check out what's at superbrightleds.com, you could lower your LED count significantly (the LEDs I'll be using have 120 degree viewing angle with 1200mcd of light output). A buddy of mine made a sign for his mom's boyfriend using 160 of those and it's extremely bright (running off a 12V regulated source).


    edit: This program is what I use for figuring out my timing. It takes a few minutes to get used to but is an eminently useful program (and it's free).
     
    Last edited: Jan 27, 2011
  9. sall

    sall

    51
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    Jan 29, 2010
    These LEDs are specifically catered for auto signal lighting. They are much better than superbrightleds.com products. They needed to be reliable and legal. You should consider them for your project. The 20mA you are using is probably not going to be bright enough during the day. You can read more about them at the links I've posted below.

    Using SuperFlux LEDs in Automotive Signal Lamps

    Electrical Design Considerations for SuperFlux LEDs

    SuperFlux LEDs Technical Datasheet


    I need so many not only to be seen in the daylight but because my tail light are tinted. There 70 in tail assembly, 60 in side marker assembly (amber and white switchbacks), and have yet to make an array for the front turn signal.

    This circuit is replacing the factory turn signal flasher. It needs to be able to handle to the entire load for L or R side of signal circuit. Thus the reason for using a transistor capable of handling this.

    I already have the timing and duty cycle down. It's set to 53% after viewing several OEM flasher datasheets and my liking. See video posted in previous thread. Its all been breadboarded and tested.

    What I am after is the most efficient and reliable to handle the load of the turn signal circuit.
     
    Last edited: Jan 27, 2011
  10. janagyjr

    janagyjr

    67
    0
    Dec 17, 2010
    While I can appreciate them being made specifically for this application, they are, in general, no brighter than what SBL offers. From the datasheet you provided, the best in that series only does 2,000mcd (or 2cd), not much brighter than 1200mcd (or 1.2cd).

    Sorry I couldn't help (I really didn't mean to turn this into an argument). Good luck and God bless.
     
  11. sall

    sall

    51
    0
    Jan 29, 2010
    Haha it's okay my friend. Wasn't just trying to argue just stating why I chose which LEDs that I did. Its more along the lines of being "legal" which these are DOT approved vs superbrightleds.com and other various resellers are not. Most doing auto retrofit are using these for multiple purposes. Having four legs also helps heat dissipation.

    Also keep in mind I am using red-orange mostly. The only amber is up front.

    I also need to have the timer output capable of handling load from two 3157 filamnet bulbs as well until I get the chance to make a custom array for them, but that will come after the HID projector retrofit... so many projects so little time. Fun to learn thoughts for sure!
     
    Last edited: Jan 28, 2011
  12. sall

    sall

    51
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    Jan 29, 2010
    So, I wanted to be for certain how much draw there was from factory versus the draw at this moment.

    I looked on Sylvania's website to get the current draw information. Here is how it coincides with my vehicle:

    Incandescent:

    Front Turn Signal/3157/2.1A
    Front Side Marker/194/0.33A
    Rear Turn Signals/3057/2.1A(2)

    Factory Total Draw: 6.63A



    Current LED Retros:

    Front Turn Signal/3157/2.1A ---- Will be chnaged to LED array before all is said and done.
    Front Side Marker/ 30 LEDs in series of 3 @ 58mA/ 0.58A (LEDs don't prove to be more efficient here over the 194 bulb, but oh well)
    Rear Turn Signal/ 80 LEDs in series of 3 @ 58mA/ 1.1A

    Total LED Draw: 3.78


    So, not too bad I almost cut the draw in half and gained some advantages along the way.

    Now, since I know the draw for certain with the current setup, I can decide what transistor or relay to use. Does anyone have any suggestions other than the BD679?

    I'm still open to relay suggestions as well.
     
    Last edited: Jan 28, 2011
  13. sall

    sall

    51
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    Jan 29, 2010
    Would I have any problems using a relay that is capable of handling a larger load? I have several of these OMRON 12088567 micro relays laying around that could be put to use.

    They are rated at 40A and I won't be pulling near that amount (see above post). The circuit is protected with a 15A fuse that I will be changing to 10A to suit the current draw.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,389
    2,774
    Jan 21, 2010
    I am unsure why you need anything special. Can't you use the same relay or whatever that was used for the incandescent bulbs?

    Sure, there can be an issue if the current falls to a very low figure with respect to the previous level, but that is not the case here. I'd try the relay you have on hand.

    And I would not be surprised if the LED replacements are significantly brighter than the bulbs.
     
  15. sall

    sall

    51
    0
    Jan 29, 2010
    Alright, thanks for the input! I'll use what i have available.

    Yes, the LED array is bright. I compared my factory untinted lenses to the LED array in my tinted lenses on the car and the LEDs even on a tinted lens is brighter. You can see a short video on the first page of this thread when testing the timer.

    Picture Comparison: LED array on left side; Incandescent on the right side.

    [​IMG]

    View of the Arrays mounted in Housing:

    [​IMG]
     
    Last edited: Feb 10, 2011
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