On and flashing rear light- Mtbr.com
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  1. #1
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    On and flashing rear light

    tune in for the latest installment in "what I can do with 1in.sq. aluminium tubing"

    my ancient cateye died a while ago and I was inspired by this thread to build an on and flashing rear light. I wanted something cheap and simple (no modes), but that would be on all the time and pulse to a brighter level rather than flashing on and off. In other words having both a steady and a flashing light in the same unit.

    Driver board is:
    http://kaidomain.com/product/details.S008617

    with an extra AMC7135 chip from:
    https://illuminationsupply.com/amc71...kage-p-71.html

    Magic sauce is one of
    these

    Switch is a Judco SPST latching from:
    http://search.digikey.com/scripts/Dk...9PB-ND&x=0&y=0
    with rubber boot (which cost more than the switch)
    http://search.digikey.com/scripts/Dk...2PB-ND&x=0&y=0

    Battery is an Accucell 3000 (2600mAh measured) I scammed off my brother

    Connectors are from a Magicshine Y cable

    Bracket is the usual Cateye spacer and handlebar combo

    LED is a spare XP-G R5 that used to be in my helmet light

    Optic is a mix of Gaggione elliptical courtesy of Of'roadbent (thanks!) and cut up Cateye reflector from the LBS bin.

  2. #2
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    The trickiest bit was getting the on and flashing thing working. After some much needed help from monokaiser, we figured out that the way to get this to work was to cut the Vdd sense trace to one of the banks of 7135 chips (normally protected by a diode) and solder the blinky in its place. The 7135 chips work by sinking current from the LED to ground when they have a suitable voltage (~3-5V) at the Vdd pin. So, by using the blinky, that Vdd voltage will only supplied when the blinky is on which will in turn turn on the 7135 chip. Blinky off = no Vdd = 7135 chip off.

    In pictures

    showing the cut trace (used a dremel tool of some description). Note - the 7135 chips have to be on separate banks unless you can cut the trace between chips on the same bank.


    Wired up with blinky and resistor (can anyone figure out the value?). I tried a bunch of resistors of known values until I stuck this one in and it work. Pretty sure it would be an empirical exercise though depending on the blinky Vf - all I had to do was reduce the brightness of the blinky until it was a tiny point, then it would fire the 7135 chip.




    tidied up and heatshrinked


    optic on and cable being sealed (I tried Oogru this time, not terribly impressed though amazingly cheap)


    Housing with chopped up Cateye reflector and an excess of 5min epoxy. It aint going to win any beauty awards, as befitting my "ugly as sin" design ethic


    Single cell marine taped and plastidipped


    It works!


    Mounted on the Trailer of Doom


    Total cost probably ~$15 including my AMC7135 misadventures. I'm extraordinarily happy with it. It's super bright and has at least 270deg visibility, which was one of my main aims. The pulsing is noticeable but somewhat subtle - I'm slightly tempted to finagle another 7135 chip onto the flashing bank to give 350>1050>350mA, but that might be overkill, even though it won't hurt battery life too much. Speaking of which, that should be ~4h or so, which'll be more than enough for me, plus the battery PCB will stop me overdischarging the cell.

  3. #3
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    oh, and I forgot to add, I have at least 10 more of these blinkies, plus a handful of the resistors that I used, so if anyone wants a couple, PM me your address and I'll pop 'em in the post.

  4. #4
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    Awesome! Looks great! Nice work m8!

  5. #5
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    thanks, you deserve a lot of the credit!

  6. #6
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    Very good!

    Could the reflector piece be heated and bent into a semi-circle? Less cutting and gluing then.

  7. #7
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    I'd imagine so, especially if you have a hot wire to help make the sharp radius bend(s). The reflector was pretty thick (hence the grinding in the middle so I could get everything to fit!) so there was a lot of material to play with.

  8. #8
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    nice job Matt !

    I really like the way to designed the reflector

  9. #9
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    thanks It's given me a great deal of comfort riding the roads at night, especially in the kind of weather (snow, freezing rain) that we're getting at the moment.

    The neat thing about using the reflector is the way it scatters light, so with the side pieces I was able to choose an orientation that directed some of the side scatter back towards the front of the bike. It worked out a lot better than I expected!

  10. #10
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    it looks like you used a white light with red reflector.

    how much current are you running through it ?

  11. #11
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    yep, a white XP-G R5 as it was what I had laying around. Base current is 350mA pulsing to 700mA when the blinky fires the second 7135 chip. I'm tempted to add another 7135 chip to the pulsing bank to make it ~1A, but it's not particularly necessary.

  12. #12
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    I am using 350mA -> 1A flash. It should be OK both ways, you see the trick is the blink to the eye, even a small amount, makes the light a thing screaming attention.

  13. #13
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    Great job matt and mano I have been following this build on the other thread. It's great to see the finished product.

  14. #14
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    Love it! I've been thinking about a DIY rear light for quite a while, even started and canceled a project. This might motivate me to start over again, thanks for sharing!

  15. #15
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    thanks all. I finally caved in and scavenged another 7135 chip to add to the blinking bank. I doesn't make it massively brighter, but it does make the blink/pulse considerably more noticeable, which is the whole point after all. Cars are now giving me a wide berth when overtaking, which is a bit of a novelty in central PA

    nioko, if you need any blinkies to help with the motivation, let me know!

  16. #16
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    I am sure it looks just gorgeous, at night, in the dark

    Having a little bit of trouble following what you have done. If I am following it correctly, then using your image


    • the trace you cut to the right of Q2
    • the resistor is soldered to the 2nd pad below Q2
    • one leg of the blinky is soldered to the resistor, the other leg is soldered to the same pad as the + wire in the middle of the board


    It appears that the 700 mA board has 2 7135 chips on one bank, which I suspect is why you chose to modify the 350mA version.

    To make one with a base current of 350mA and pulsing 1050mA, I am right in thinking the easiest way is to start with 1050mA board and wire the resistor & blinky to the side with 2 chips ?

  17. #17
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    Quote Originally Posted by mattthemuppet View Post
    nioko, if you need any blinkies to help with the motivation, let me know!
    Thanks for the offer, Matt. I'm living in Switzerland, so I don't think that it's worth the postage, considering that they cost $1.46 delivered to my home.

    I've got a lot of other things to do before starting that project, but I guess I'll order the parts soon, so I have em around when I want to start building the light.

    cheers, Nioko

  18. #18
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    Quote Originally Posted by find_bruce View Post
    I am sure it looks just gorgeous, at night, in the dark

    Having a little bit of trouble following what you have done. If I am following it correctly, then using your image


    • the trace you cut to the right of Q2
    • the resistor is soldered to the 2nd pad below Q2
    • one leg of the blinky is soldered to the resistor, the other leg is soldered to the same pad as the + wire in the middle of the board


    It appears that the 700 mA board has 2 7135 chips on one bank, which I suspect is why you chose to modify the 350mA version.

    To make one with a base current of 350mA and pulsing 1050mA, I am right in thinking the easiest way is to start with 1050mA board and wire the resistor & blinky to the side with 2 chips ?
    that's exactly right, although after adding another 7135 chip I had to solder the resistor end of the blinky to the chip leg just above and to the left of Q1. It's on the same trace, I just found it marginally easier to solder to.

    I actually started with the 350mA boards as I though that would be sufficient for a rear light. It was only when I saw your thread and monokaiser's replies that I got to thinking about doing it this way. A 1050mA board such as this one would make life considerably easier . In fact, if that really is what you'll get, then it'll be even easier, as all you'd have to do is remove the diode to the bank with 2 chips on it, then solder the blinky across the gap - no trace cutting required.

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