# My first build - 3W Red tail light



## Rekkie (May 26, 2011)

Being my first "from scratch" build I decided to do something small. I do a lot of day time riding on the road (on my road bike), and I had a couple of close calls before with motorists not "seeing me". Although I think that's B.S. I know it does happen sometimes. I started using the average 5 LED red taillight, but it's not that visible in day time from a distance of say 30m. So rather than not being seen I decided I'd slightly "blind" them and BE seen.

The idea was to make a very tiny light unit with a separate battery unit that pops into the saddle bag (or can be strapped to the frame if necessary)

The parts:

-Using a 3W Red LED and 20mm 60 deg lens bought from a local company.
-My self-built 555 chip based "flasher" circuit with voltage regulator and transistor to deal with the high current...25% ON - 75%OFF duty cycle @ about 1.5Hz rate. Also found that if I use 2*CR123 batteries in series the light is twice as bright
-Ultrafire 18650 battery case
-Clicky switch
-custom made body and mount.

Holding the _newb-name_ high, I unfortunately don't have any pics of the led...I glued the LED to the body and popped in the lens which was a tight fit and can't pull it out again the rest is of the completed light. Camera set for normal daytime shooting...pics taken aprox. 4 PM

The "flasher" unit plus battery case ect.









The light on my bike



























And daylight shot (had to use fast pace shooting to catch the flash so excuse the blurry pics, will use tripod next time)









[email protected] 80m distance









If anyone wants to build something similar I'd be happy to help/share the flasher circuit's parts info ect.


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## BKruahnndon (Jul 17, 2009)

Very cool.
I'd be very interested to see more info on it.


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## emu26 (Jun 23, 2008)

Nice work Rekkie. a couple of small holes drilled into the side near the optic will give side illumination as well.

Yes, please post circuit drawing for the flasher


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## rschultz101 (Oct 5, 2009)

cool beans! 
send some info, maybe I'll make an neat layout out of it.

cheers, again !
think, it's time for some , bike daytime lights.
this one should fit the bill, for the tail light.
cheers, Rob


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## mfj197 (Jan 28, 2011)

Good stuff Rekkie. I like the driver work. There is a dearth of good blinky drivers as the frequency of the drivers we normally come across is rather too high and is more liable to give other road users epilepsy rather than make the roads safer for us cyclists!


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## Rekkie (May 26, 2011)

mfj197 said:


> There is a dearth of good blinky drivers as the frequency of the drivers we normally come across is rather too high and is more liable to give other road users epilepsy rather than make the roads safer for us cyclists!


Agree!!

I'm still searching for the circuit diagram I drew, I built the circuit a couple of months ago. But here is a basic diagram I found on the net quickly. Only difference is I'm using a power transistor which is triggered by pin3 to switch on/off the LED as the 555 timer chip (IC) can only handle 100mah output if I remember correctly. And an adj. voltage regulator to regulate the voltage/current to the LED. The duty cycle is determined by R2 (think I used 16 ohm) and R3 (think I used 80 ohm) and the cycle rate (in Hz) is determined by the Cap C2 (I used 4.7uf) across pin1 and pin2. I left pin5 open. and I left R1 out. Nice thing is, the input voltage is very flexible, up to the max of what the 555 can handle. I tested it up to 15V and it got brighter from 3.7V to 9V, but after that it remained the same, but the voltage regulator got really hot then, as I don't have space for a heat sink inside battery case for it. 8.4V is about the max input to ensure it doesn't get too hot.










In short, it works by charging/discharging the cap (C2 on drawing) through resistors R2 and R3, each time the the cycle changes from _charge - discharge - charge_...it triggers pin3 ON/OFF. So the bigger the cap, the longer the cycle takes if you keep you resistor values the same...the slower the "strobe" and the smaller the cap the....think you get the idea

If I don't find the drawing by the end of the week, I'll redraw it for you guys


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## Rekkie (May 26, 2011)

Almost forgot. 2 good links too help out:

555 and 556 Timer Circuits

The 555 Astable Circuit - Electronics in Meccano


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## vroom9 (Feb 24, 2009)

The 555 is rated at 200ma max output. 

It is a bit stronger at sinking current than sourcing though. To do that connect the LED to the positive voltage and then the resistor to the 555 output on pin 3.


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## Rekkie (May 26, 2011)

vroom9 said:


> The 555 is rated at 200ma max output.


Yes that's right! I didn't have the datasheet with me when I posted so had to do from memory.

The LED I'm using draws ~230mah (measured) when using 1*18650 and ~660mah when using 2*16340 so the 555 won't hold up on its own.


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## Toaster79 (Apr 5, 2010)

Nice Build!

Made one myself some time ago


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## Rekkie (May 26, 2011)

Toaster79 said:


> Nice Build!
> 
> Made one myself some time ago


Good build!

I used this type of lens to give me an even 60deg beam. will try and get a proper beam pic up. And I used this 3W red LED. Both lens and LED bought from local supplier. The LED seems to be putting out close to 100 lumen when at 8.4V input, using 3.7~4.2V input seems to produce around 60 lumens...compared it with a Ledlenser H7.

Here is the circuit drawing, hope it makes sense:









Values I used (relative to my drawing)

R1= 16 ohm__0.25W
R2= 80 ohm__0.25W
R3= 100 ohm__0.25W
R4= 100 ohm__0.25W
R5= 90 ohm__0.25W
C1= 4.7 uf


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## campag550 (Sep 19, 2011)

*3w tail light*

Sweet Build Rekkie!

Im going to take you up on your offer and have a go myself.
Im not an electrical guru like yourself and need a hand up! What value diode did you use near R2 and what type /value transistor ( well, thats what I think it is) did you use near R3?

ATB

Pete


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## Rekkie (May 26, 2011)

campag550 said:


> ...Im not an electrical guru like yourself and need a hand up!...


Thanks but I'm more of the "hobby-electrical-figure-it-out-along-the-the-way" kind. So it usually takes some trail-n-error before I get it right.

As for the transistor I used an ECG 157 NPN power transistor. you can basically use any NPN transistor that can handle the current you want to source to the LED. I used a TO-220 package for the transistor...same for the voltage regulator, as that (TO-220) package is easily available.

As for the diode,I think you can use any diode (NOT Zener-diode), as it's primary function is to stop "feedback" into circuit...*but I'm not sure*...I had some funny flickering of the LED happening at first and my old man (who is the actual elec-guru) suggested I put the diode in. He explained why, but I lost him half way through the conversation, and this is as much as I can remember 

Hope it helps!

ATB with the build and give a shout if you need help...will do what I can / know 

Oh, almost forgot: since I had the light on my bike and using 2*16340's input for some extra brightness, I could see a real change of behavior from motorists passing me. Haven't had any tight passes or mirror bumps...*touch wood* so that's mission accomplished for me


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## campag550 (Sep 19, 2011)

Thanks Rekkie!

Still leaps and bounds ahead of me then. I usuall have two extremes. It either doesnt work:madman: or it works sooo well it melts. I take it the aluminium housing acts as the heat sink for the 3w led. Does it get warm/toasty?

P


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## Rekkie (May 26, 2011)

The LED does not build up much heat that I can tell. It kinda remains at body temp. +/- 35 deg C. I had it (LED & circuit) running for +/- 2hours off a bench supply with no heat sinking, just the LED + Star. The voltage regulator however does get hot when the input voltage is above 9V so I would not recommend more that 2*Li-ions for input if the voltage regulator has no heat sink.


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