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Thread: Designing good daytime rear commuter lights

  1. #211

    Default Re: Designing good daytime rear commuter lights

    I saw this and I thought it would be clear when I revisited. Is the word 'multivibe' and is the 'other output' the 'LED driver circuit' where you duplicate the dotted outline circuit?

    The 0.35 Watt 5.8 lumen LEDs are interesting.

    BrianMc

  2. #212
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    Default Re: Designing good daytime rear commuter lights

    Hi Brian.
    The answers are "Yes" and "Yes".
    The multivibe (multivibrator) produces the timed signal that turns the 2 LED drivers on and off (ie one turns on when the other turns off).
    The LED drivers switch the current (on and off) that goes to the LEDs.
    The current flowing through each LED is determined by the resistor in series with it (the 1.5 ohm R in this case).
    Since the supply voltage is 3.3V and there is about 0.3V drop across the switching transistor when its turned on and about 2V across the LEDs that leaves a 1V drop across the series resistor which gives a drive current of 1/1.5 (I=E/R) or somewhere slightly north of 666mA.
    Purists and young circuit designers please note that I know this is a rough estimate only but thats how many fine things were prototyped back in the Dark Ages when something called a slide rule was the Lab computer!

  3. #213

    Default Re: Designing good daytime rear commuter lights

    I built electronic kits including Dynaco's AM-5 tuner, or much more recently built up Martin's Circuit 12 dyno board. I have not bread boarded any novel circuits. Familiarity with the concepts is not the same as hands-on experience. Like sex education versus being sexually active. My Hughes-Owens SR is waiting to be framed for display. A thing of beauty is a joy forever. It was an award for winning the high school Math contest. I am chelating Heavy Metals to regain my health and that drops the IQ a tad. So I appreciate the clarification.

    Looks like using DX's 5 volt and modifying values would allow 2 series CREE XP-E Red-orange LED's and twice the number of .35 watt ambers or a or maybe 4 2S2P XP-E ambers (0.5 A max) should work.

    BrianMc

  4. #214
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    Default Re: Designing good daytime rear commuter lights

    Should work "a treat" and emit an awful lot of light.
    The transistors I used are universally available and dirt cheap (great pun for something made out of silicon!)

  5. #215
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    Default Re: Designing good daytime rear commuter lights

    The light in post 208 might be on its way to the History Museum!
    I was in my car a week ago and noticed one of those led emergency traffic noticeboards (in full daylight)...thought "those leds show up ok in daylight!"
    A little research and I discovered CREE Screenmaster 4mm x 5mm leds. Made especially for outdoor displays.
    Cutter were kind enough to sell me a few and mixing them with the yellow leds from 208 gave me:
    http://img268.imageshack.us/img268/6353/k4ub.mp4
    As you can see I weakened and used a microprocessor this time.
    Now all I have to do is shift the prototype to the bike!

  6. #216

    Default Re: Designing good daytime rear commuter lights

    Interesting. I have my order on its way with three XP-E Red oranges for a dyno tail iight as 1S3P serial with the head light. That should be about 100 lumens, or the power of three Turbos, using a flare lens on each for a 15 x 70 degree FWHM beam on each, with the outside ones aimed at an angle (30-45 degrees) to the bike axis. Martin's circuit I am using was for about 10 Vf of Luxeons, and i will have about 10 Vf of XP-E and XP-Gs. If I change out the doubler board I can up the rear array to 3s1p and 300 lumens.

    No fancy flashing though.

    BrianMc

  7. #217
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    Default Re: Designing good daytime rear commuter lights

    Follow up re post 215.
    While I thought it looked great close up (both the colour change and the clever flash pattern) it was a failure.
    Even at 30 meters it was disappointing and would not attract a lot of attention since the detail of the pattern was lost due to the small size of the LEDs. Plus the busy colour change pattern was too fast and ended up “a twinkle”.
    “Twinkle twinkle little light, I don’t want you upon my bike”
    So….Back to the light in post 208.
    I reprogrammed the microprocessor to give a more sedate and traditional flash/colour change pattern and I can assure you that is much more visible.
    http://www.youtube.com/watch?v=nBVcdcifsWk

    Lesson learned: The apparent size of the light source is important and complicated high speed flashing is not very effective.

  8. #218

    Default Re: Designing good daytime rear commuter lights

    Quote Originally Posted by 1 what View Post
    I reprogrammed the microprocessor to give a more sedate and traditional flash/colour change pattern...
    Hi 1what,
    Great light!!! But can you elaborate on your 'reprogrammed the microprocessor' statement please. Maybe I'm missing a 'humorous aside' but I thought you said 'microprocessors were for twinkies' or something similar! The idea of slowing down the rapid flashing makes a lot of sense to me...
    ta,
    Savvas.

  9. #219

    Default Re: Designing good daytime rear commuter lights

    That is an interesting light. If I calculate output to lumens and lumens per watt, the small LEDs are about 20 lumens per watt, while amber XP-Es are about 100 lumens per watt, so I wonder about using an acrylic tube as a fiber optic fed by an amber XP-E on each side as being bright top or bottom isn't as important. The vertical flashlight on the back so it is up over at least some SUV's using a similar setup may be much better than a turbo on the back of the helmet. I an old thread they said that the PBSF was the ultimate answer. Apparently not.

    BrianMc

  10. #220
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    Default Re: Designing good daytime rear commuter lights

    In order of posting:
    Savvas - Yes microprocessors are for yuppies but when I was flirting with a more complex flash sequence they were the only way to go since you have infinite and rapid control over the sequence of loght flash as well as colour change and I was in the mood to play!
    Since I already had the LED driver built it was easy to reprogramme it for the new slower sequence.
    As an aside it was the first time I've used them in a light and it was very interesting to see how different sequences looked. I now have no doubt that some sequences attract attention much better than others. The rule of threes seems to apply with 3 flash ptns being especially potent. Longer complicated ones just dont "grab".
    Also when using 2 colours it was more attention getting if one of them looked brighter than the other. When the Y & R were equal it was nowhere near as efffective (it's easy to adjust by altering the current setting resistor in the driver). I chose to set red brightest since it is a tail light.

    Brian - Care to upload a rough drawing of what you suggested?

  11. #221

    Default Re: Designing good daytime rear commuter lights

    I am a newbie on the bicycle, newbie on the commuting, newbie on the nightriding, and a newbie on lights. With that said, I started with a cheapo rear light out of wally mart. I have moved up to a Planet Bike Turbo Super Flash. Way ahead of the cheapo, but from what I have been reading in these thread, I am barely minimum!!

    I am running a PB Blaze 2w up front, and a PB beamer on my helmet. Still, from reading this thread, I am barely minimum. That is good, because I am finding out, although fun, that riding in the night with traffic one has to be on that ball. It is fun, but it is no joke out there, and I see that I need to be seen.

    Just joined this forum, and I joined to LEARN..

  12. #222

    Default Re: Designing good daytime rear commuter lights

    Quote Originally Posted by 1 what View Post
    In order of posting:
    Savvas - Yes microprocessors are for yuppies but when I was flirting with a more complex flash sequence they were the only way to go since you have infinite and rapid control over the sequence of loght flash as well as colour change and I was in the mood to play!
    Since I already had the LED driver built it was easy to reprogramme it for the new slower sequence.
    Thanks for the explanation. I'm keen on having a go at replicating your cigar light. Trouble is, I can't see the microprocessor on the circuit you showed us in post 208 (or thereabouts)! What am I missing...?
    Savvas (on leave and in avoidance mode with a long list of house maintenance tasks!)

  13. #223
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    Default Re: Designing good daytime rear commuter lights

    Hi Sam,
    Always happy to help a chap avoid household tasks!
    It's a different circuit altogether.
    I'll try to draw it (and post) later tonight.
    Tom.

  14. #224
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    Default Re: Designing good daytime rear commuter lights

    Savvas,
    Here is the cct using a picaxe 08M2 driving mosfets to turn the LEDs on and off.

    Both the R&Y LEDs had the same on/off sequence:
    ON 0.1 sec - OFF 0.1 sec - ON 0.2 sec - OFF 0.1 sec - ON 0.4 sec - OFF 0.1 sec
    The 2x 2.2 ohm resistors (by pure good luck) gave me a current of 740ma in the red CREE and 860ma in the 9 yellow LEDs.
    I chose to run it all at 3.3V to minimize the voltage drop across these series resistors and max the efficiency.
    PM me if you want further details.

  15. #225

    Default Re: Designing good daytime rear commuter lights

    i what,
    OK - I can see now how I got confused! After abandoning your 'twinkle' light you've gone back to the 'cigar' model but elected to use the afore-said light's yuppie driver instead of the multivibrator! I've been refusing to learn about these 'picaxe' thingumys for years - I can see I'm going to have to spend some time with wikipedia!
    While I thought the Enterprise was v/elegant (and I've been trying to copy it) the cigar model seems more practical in some ways. Is that a fragment of ping-pong ball at the end that you have the Fenix diffuser mounted on?
    Savvas.

  16. #226
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    Default Re: Designing good daytime rear commuter lights

    Hi Savvas,
    Yes – the “cigar” light with the “twinkle” driver.
    The picaxe microprocessor is very inexpensive and very easy to use in this type of basic way (that’s a pun since it uses “basic” prog language) if you’ve had any electronics education. Well worth the day or so you might spend getting familiar with it (again - PM me if you want any help).
    See:
    http://www.picaxe.com/
    plus Wikipedia.
    I agree that the “Enterprize” is v elegant and it was hard to move on from it but the addition of a second colour plus the size increase worked better especially from the side. BTW I think you’re being polite calling the new light “cigar” shaped. I think it looks more like a flying p****** (Greek word rhymes with challis). I looked at modifying the earlier light to get some yellow LEDs into it but it would have wrecked it….pity.
    The half pingpong ball is actually half the ball from a roll on deodorant. They are much more solid than pingpong balls and cost zip. They also make excellent diffusers.

  17. #227
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    Default Re: Designing good daytime rear commuter lights

    They also make excellent diffusers.
    This was going to be my observation. The obsession with ultimate million-lumen LEDs seems to over-reach itself. Commuting, driving and just watching what's going on, I've come to the conclusion that bright enough can be easily reached. What is less well done (it seems) is making the illumination big enough. An eye-gouging pin-prick of light is hard to place and easier to ignore, whereas a dimmer but wider source of light is much more quickly recognised. Look at the back of any motorcycle or scooter. They could easily reduce the size of these lights and make them brighter but don't.

    My B&M standlight on the rear face of my pannier rack is degrading in standlight duration, its replacement might be the reflector and diffuser off a scooter with something a little more home-brew inside.

  18. #228

    Default Re: Designing good daytime rear commuter lights

    Quote Originally Posted by jdp298 View Post
    This was going to be my observation. The obsession with ultimate million-lumen LEDs seems to over-reach itself. Commuting, driving and just watching what's going on, I've come to the conclusion that bright enough can be easily reached. What is less well done (it seems) is making the illumination big enough. An eye-gouging pin-prick of light is hard to place and easier to ignore, whereas a dimmer but wider source of light is much more quickly recognised. Look at the back of any motorcycle or scooter. They could easily reduce the size of these lights and make them brighter but don't.

    My B&M standlight on the rear face of my pannier rack is degrading in standlight duration, its replacement might be the reflector and diffuser off a scooter with something a little more home-brew inside.
    Multiple side-by-side lights look bigger, too. The Red Zone 4's showed that if you have the power, you can spread the beam and increase coverage while not losing visibility at a distance. So I removed the reflector from my DIYs and placed a narrow beam thrower (HotSpot) between. Distance and coverage. When the LEDs arrive I have a dyno tailight to build that will use a 15 x 90 degree FWHM lens on three LEDs, one aimed straight back, one to each rear quarter. The light/reflector will be the width of my rack. Under driven as a 1S3P in series with the headlight, it should be about 100 lumens into a 30 x 270 degree beam. We will see if that works well or not. BTW, some (not most) of the scooter lights here are pathetic, others are quite good. So size isn't everything. We also have to stand out from other light noise and be picked up by the subconscious of inattentive drivers. A bigger task than it was before cell phones.

    BrianMc

  19. #229
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    Default Re: Designing good daytime rear commuter lights

    Got there. the Lucas 525 motor-bike light. The fitting bolts are a thread-width wider than the standard holes at the rear of a rack, but we can get round that...

    Got a half-watt red LED and my normal standlight circuit in there. Pictures here:

    http://www.flickr.com/photos/jdp298/...7626884852454/

    The faceting of the inside of the lens makes anything diffuse. I went with the red LED rather than a white one because all the red plastic is essentially a red filter. All the other wavelengths from the white LED would be wasted. The width of the light is good, as is the depth of the sides; this makes me much more visible from the sides too. It replaces a B&M toplight standlight plus. It's much brighter, visible from a wider angle, lasts longer and still cost less than the B&M all in.

    Tenner for the motorbike light off ebay and 18 quid for everything else from Maplin. Contrast with about 30 pounds from anywhere for the B&M thing, which has degraded to the point it won't stay on for more than 20 seconds now. I don't think I can justify selling it on ebay now, so it might get "investigated". <<smiles>>

  20. #230

    Default Re: Designing good daytime rear commuter lights

    Hi jdp298,

    I recall posting the circuit for the B&M Toplight here at cpf sometime - I cribbed it from Olaf Schultz's site a while ago. It's a very simple circuit - quite similar to a lot of 'doodling' that appears here!

    Savvas.

  21. #231
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    Default Re: Designing good daytime rear commuter lights

    I remember seeing it. It was very simple. The current one has more components, way more components. I'm guessing they have a ZXSC310 and a timer cct in there. The brightness remains constant and used to turn itself off after 4 mins. Nothing conceptually hard, but I use vero-board which takes up more space.

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