At the risk of walking that line between seriousness and bad puns, an underlit bike and an under-lit bike can be the difference between life and death. Almost all bicycle injuries and fatalities involving cars find a driver saying, "I never saw the cyclist." Don't trust your life to some silly little blinky -- get noticed.

Using a handful of LED's, a dead network cable and a few rechargeable AA's, we're going to get noticed: by drivers, by the more attractive other bicyclists, and possibly by the Trunk Boiz.

All while giving a complete beginner's guide to parallel circuit wiring and low power, energy efficient electronics. Yowza!

Some Background Theory

First, a quick, somewhat inaccurate, good-enough lesson in circuits: (or, skip to the instructions) Current flows through wires like water flows through a series of tubes. The amount of current, usually measured in Amperes, is the rate of movement of charge in a circuit. Think of voltage like a body of water, resistance as the size of a hole in the container of that water, and current like the resultant water pressure flowing out: a firehose of 10 Amps is going to have more kick than a water fountain of .025 Amps, even if the firehose blasts once and the fountain runs for an hour. Consequently, trying to force a firehose worth of current through a drinking fountain is dangerous and hilarious.

We're not using dangerous power here, so the only thing you might do is fizzle out your LED. Check the forward-voltage and preferred current when picking up LED's: these are about 3.6V fwd-volt and prefer less than 25 milliamps (.025 Amps). Putting 4V at .025amps through them will shine bright at the cost of lifespan. 3.6V at .010amps will make them very dim. 9V at 10amp will make them glow extremely bright for a second before burning out (try putting the legs on a 9V battery and see!)

For simple circuits like this, (Voltage in volts) = (Current in Amps)*(Resistance in Ohms), more famously Ohm's Law, V=IR. Do the maths.

When flowing through conductive material, current flows from the (+) to the (-) of your battery, taking the path of least resistance until it can go back home (like so much Liberal Arts student.) In our water analogy, imagine poking small holes in a high pressure water main -- the water will spit out the holes, 90degrees to the flow, but it mostly continues down the tube (it doesn't stop and wait its turn to squeeze out.)

A diode, unlike a normal conductor, has a forward direction -- current will only flow through the diode in the proper direction, and will not flow at all if you stick it in backward. Also, as the current has to *do* something (heat up and emit light) inside our light-emitting diode, it is clearly not the path of least resistance. So, in the picture below, some current trickles through the diode, but the main flow is still down the wire.

Look closely at your LED. You'll see two, tiny flags, one about twice the size of the other. Current flows from the small flag to the large flag. If it helps, think of the flag being so much bigger because it needs to "catch" the current.

Enough Theory, Get to Wiring

With all this in mind, we get to wiring. If you've never soldered before, it's an essential and easy skill, and a great beginner's guide to soldering can be found here. Realizing that current prefers the path of least resistance, the wire on the right will "fill up" with current, and then squeeze through all the LED's equally. This is called wiring in parallel. Had the LED's been single file along the path of flow, instead of in the ladder-formation, it would be a series circuit.

If I were less daring I'd use resistors. They're basically unnecessary for this setup, so I left them out. If my electronics/physics instructors are reading this, I do apologize.

I've soldered the negative sides of the LED's to each other, and the positive sides similarly. Now, you can solder the wires to either side of any LED, and the entire array will light up. Going back to the schematic above, putting the wires on either side of the ladder, anywhere, will put the current down the wire first (least resistance) and through the LED's equally, second.

On my bike, I used 3 LED's facing forward and 3 facing back, all electrical taped to the frame under the bottom bracket. This keeps it effectively invisible, besides the light. You can bend and shape the array to point the light wherever you want it focused -- I usually prefer having them aimed at the street beneath and next to my tires. This reflects off the wheels, reflectors and pavement, and gives the most distant and widest visibility, while making use of motion to draw attention.

Now, slice the network cable open and choose a twisted pair that matches your bike. This bike is blue, so I went for blue/blue-white and designated blue to the anode and b-w to the cathode to keep track of them, and later stuck the green/green-white pair to a pair of white LED's refracted through scratched-up glass on the front (explained and instructed elsewhere on Prodromic.) After a quick look at the wires to make sure there aren't any obvious cuts or breaks, wire one end to your light array, and the other to a terminator, by using a pair of scissors to gently cut, pinch and pull the last 1/4 inch or 1/2 cm of blue covering off the copper wire inside. The terminator in the picture to the left can be picked up at electronics stores for about a quarter, or made from old 9-V batteries, as described elsewhere on the site.

Finally, I've temporarily stuck four 1.2V rechargeable AA's into a battery holder I purchased out of laziness -- I'll make one later.

The finished product for about 10 minutes of work and about $1.50 in parts (not incl. the rechargeable batteries):

(Pictures coming soon -- like, around nightfall.)

Here's one in a pitch-black room -- the lighting set up in this article is the only source of light. Realistically, you'd also have street lights, the moon and stars, and car headlights contributing. (Note: oops, I just realized my reflectors are missing!)

It actually looks much more vivid and cool outside, especially in the rain and on wet roads, when you'd need it most.

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