How do I make 10mm LED lights Strobe

[hootie26]

I know how to wire LED's into a 12 volt source with a resistor but could use some help on a project. I want to take (5) of the 10 mm LED's and make them strobe when I put my brake light on. I know that I will have to wire them in to the brake light circuit on my bike but could use some help with what I would need to buy and how to tie it in to make them strobe. I'm lost when it comes to the things that it will take to make them work. could i get the stuff i would need at a radio shack. Would appreciate any help, thanks hootie..

 

[MikeMl]

Bad Idea! Strobing brake light could be mistaken for a turn signal. Probably not legal, either...

 

[hootie26]

hey mike, yes they are legal for the motorcycles now, as a matter a fact they have about 5 or 6 different patterns that the LED's flash in but all I want them to do is just strobe. Motorcycles have gotten a few brakes in the laws here in the last year or so because thay need to be seen better and the strobe lights are making for fewer accidents, they just can't run the red or blue that flashes on the front of the cycle. thank you for the reply

 

[panic mode]

so what is the problem?

note that LEDs are nonlinear so you need to use series resistor. say you have LEDs that draw current If and have forward voltage drop Vf.
it is typical for LEDs to be somehting like
If=20mA
Vf=3.2V

note that we need some "room" when it comes to voltage drop across resistor for it to do it's job. ideally we would want to minimize this for better efficiency but that won't always work.
something like 1V should be bare minimum because voltage of vehicle battery fluctuates. the more voltage is across resistor the more linear response you get and less change in LED brightness when battery voltage fluctuates, but as mentioned this reduces efficiency.

for example if your bike uses 12V battery then you can have up to 3 LEDs in series in this example because that would get you to
3*Vf=9.6V and that leaves some 2.4V for resistor.

if you add one more LED, you are out of luck because this would have 4*Vf=12.8V which will not allow LEDs to lit up brightly even without resistor.

if you have more LEDs, you can use them in groups of 3 (connected all three in series and with a series resistor) but you can power each group in parallel.

now to make a strobe, you will need something that will produce several pulses (strobe).
this can be done using different methods. you could use microcontroller (they require programming) or a pure hardware solution with 555 as oscillator and 4017 as counter and decoder, something lsimilar to circuit like this:
**broken link removed**

but some people have already done it too, here one example:
**broken link removed**

 

[MikeMl]

So, by strobing, do you mean just flashing on/off, or is the flash pattern more complicated than that?

 

[hootie26]

i would like for it to strobe for a few times then go steady then soon as you let off the brake and then apply it again it repeats itself. I can more than likey tell that it would be best for me to probably just buy one, i didn't know how hard it was going to be to build it but believe its definetly out of my experience level.