Black Blade

Hello, it has been 20 yrs since I went thru college for electronics...was never able to land a job in the field tho unfortunately, and as time went by I dabbled a bit in a few simple circuits when I needed something around home for thing or another. So to say my electronics knowledge is rusty would be an understatement, but do have a very basic idea still...enough to want to tackle this project now for my bicycle (riding to work since gas prices are nutty!)

I salvaged from a scrap bin at work, a few of the LED brake light units that were incorporated into the spoiler, with the thought to turn them into a back light for my bike. The streets I need to travel on are quite busy, so any extra visibilty is a bonus!

All the unit needs is 12 volts applied to the wires (will be using a 12 V ATV battery) and she works like a charm, but what I would like is to have is a method to have the tail light flash similar to the little bike lights people use on backpacks etc, and also have the option for it to stay on solid.

As soon as I thought "simple flash circuit", I recalled the 555 timer IC in my dust covered memories So went to Radio Shack (Circuit City now) and managed to find one 555...they hardly have any components anymore. I recall being able to go in there when in college and being able to get all kinds of stuff...they don't even carry the solderless breadboards anymore!!

But can order whatever I need thru internet I suppose...I was hoping that given the parameters of my project, some of you fellas would be able to let me know how to lay out a circuit for this (resistor and cap values etc).

I was thinking that the flasher to be on for half a second and off for the same time would be good enough...or I can also put a pot in, to dial in the right frequency of flash.

If anyone could sketch me up a circuit and email it to me, I would really appreciate it.

Extra thought: I was thinking about putting some small contact switches on the brake levers to activate the brake light, but I guess that could be wired separately from this other circuit?

mneary

Google comes up with some nice circuits with 555 led flasher. One of them is at http://wild-bohemian.com/electronics/flasher.html When I see flashing bicycle lights on the road, they are much faster than once per second, more like two or three.

colin mac

Here's another 555 circuit, flashes the led at 3Hz. Should be fine.
http://www.kpsec.freeuk.com/projects/flashl.htm

kchriste

You know, you can buy these little flashers for next to nothing. They run on 2 AAA's and will run for much longer than a power hungry 555. Unless you are doing this for the educational value of it, just go out and buy one for $5.

__________________
--- The days of the digital watch are numbered. ---

Black Blade

I know about the little lights..have two, but since I got this nice wide LED array from an actual car, so it will be much more visible (safer) I would like to use it. I actually have two of these third brake light LED arrays, so I could hook it up the use the alternate flasher type of set up with the 555.

I will also be looking into making up a front light of some sort, with some kind of bright white LED's. Looking long and hard at some flashlights that use LED's and run on 6V...but then would have to reduce the 12 volt from the battery...would rather not waste the energy across a resistor but instead use LED's that can handle the full 12 volts.

I have one of those CCM Evox bicycles, which looks a bit different so I can be more creative with accesories for it...lol. The ATV battery can be recharged each night on my battery charger, but don't imagine that my 15 minute run to work when I will require the back light on will use up the whole battery life (no idea what kind of power drain that LED array would have).

'Sides...there is many things that we can buy instead of making it from scratch...but what fun is that?

kchriste

For the front light you could organize the white LEDs into groups of 3 LEDs in series. Then you'd only waste apx 3V across some resistors.
Measure the current that your "wide LED array" draws. You may need a transistor or FET to drive it from a 555.

__________________
--- The days of the digital watch are numbered. ---

Black Blade

I measured 175 mA for my array with the 12 volts applied. Would I need a transistor to drive that?

kchriste

It is close to the 200ma limit for a bipolar 555. So yes, I would use a transistor to maximize the voltage to the array and reduce the stress on the 555.

__________________
--- The days of the digital watch are numbered. ---

Black Blade

Ok, so how would I go about constructing this type of circuit? I still have to find myself a breadboard to try out the circuits....d**n radio shack!

kchriste

You could build something like this:

http://ourworld.compuserve.com/homep...Bowden/555.htm
And just leave the 2N2905, diodes and 100hm: resistor out. You should change the 220hm: resistor to 560hm: when operating the circuit from 12V. Replace PR3 with your array.

__________________
--- The days of the digital watch are numbered. ---

Black Blade

thanks...soon as I get a breadboard and the components will give it a whirl..appreciate the help