Introduction: Automatic Bicycle Light From a Plastic Bottle

By Bicyclosis!
About: Crazy about bicycles, outdoors and diy projects

Bicy light was a crazy idea I had while ago when I was bike touring in Peloponnese and I was passing by garbage after garbage on the side of the roads. Right then, I was so frustrated with the sight of endless plastic flooding every magical place I've encountered, that I knew I had to think of something useful from this polluting material. After hours of daydreaming I had the basic concept in my head. A bicycle light made out of plastic bottles. I wanted it to be very small, waterproof, bright, tough and as efficient as possible so it wont eat batteries like candies. But even with the idea completely formed in my mind, in reality it seemed like an impossible task. After many frustrating months of thinking, sketching, trying things (and a precious helping hand from my friend 'Gearloose ' FIlippos) and battling with the urge to quit, I've come up with the basic design that seemed to be working. After some more days I had the prototype. I was so happy I can't describe it. And all that for a tiny bike light that I could find on ebay for 1$. But mine is made out of garbage that I found on the streets and it's much better than anything else!

What we are going to need:

  • Reed switch
  • Plastic bottle
  • 20 oz style Plastic bottle caps (2)
  • Rust-proof wire - An old, plastic-coated coat hanger might look nicer
  • 1-watt LED Solid core cable
  • (1) Small piece of wooden branch
  • Inner tube
  • Soda can
  • Small magnet.At least 8x2 mm. You can find these in old, broken headphones (or buy on ebay)
  • Zip ties
  • Coin-cell battery
  • Speaker wire
  • 10 ohm resistor

Video from an older version of the light (less bright):


And how it performs (this version):

Step 1: Prepare the Casing

  • First, scavenge two bottles (ideally from the same brand) from the trash. It doesn't matter if the bottle is dirty, crushed, or destroyed as long as the part near the cap is intact.
  • Use a good razor to cut away most of the bottle and leave the part near the cap. Remember to leave enough so when later are fitting the cap, the part near the top should go inside the cavity of the cap (as it happens when you screw a cap on the bottle).
  • Then put the cap on a piece of paper and draw a circle around it. That's the circumference of the cap. Use that as a reference for your bottle so you know how much you should cut. You'll want the cap to fit snugly, so regularly check to make sure the cap fits on the open part of the bottle you just cut.

Step 2: Fit the Cap on the Bottle

  • If the new cap fits, but it doesn't sit perfectly, use a butter knife to open it. Then, with the razor, carefully remove some more plastic from the bottle and try again. It should make some nice clicking sounds as you press them more and more together.
  • When you have it ready, take the cap that's not screwed on the bottle, and using your razor open a big hole on it. The hole should be as big as the size of the cavity (that means you shouldn't destroy the cavity inside - See the photo).

  • Cut off the plastic ring in the middle. We need this part to be transparent plastic so the light can be seen from 360 degrees.

Step 3: The Transparent Front Cover

  • Using again the body of the bottle, cut out a circular piece of plastic big enough to fit snuggly on the cap you just made a hole on. As you push it with your finger inside the cap, it should make click sounds until it touches the edges of the cavity. For better insulation, put some silicone glue around the cavity where the circular piece is going to sit on.

Step 4: Cut a Plastic Frame to Hold the Electronics

  • I have many designs for this skeleton, but I am going to mention here the easiest.
  • Cut again a circular plastic piece from the bottle body slightly bigger than the front cover (3-5 mm).
  • With a pair of scissors cut a cross without cutting the center. This is where the led is going to sit on. Please have a look at the sketch and the photos to understand the concept.

  • Seat the LED on the base facing the cap (so it's upside down). Use a pair
    of needle nose pliers to straighten and then bend its little metal ears downward. Then, place it on the hole so its lens protrudes from the other side and make the metal ears go through the holes to the other side.

Step 5: Connect the Electronics

Flip the base over so you can see the metal ears. Use needle-nose pliers to connect the resistor to the negative side (you can see a little minus) and a piece of cable to the other one. Take a look at the pics for an example.

Step 6: Prepare and Place the Battery

  • From an aluminum can, cut out two discs the size of the cap. Use sandpaper or a Dremel to scrap off the plastic layer from the side of the disc (just one side).
  • Sketch with a pencil the shape of the plastic skeleton and drill four holes just outside it (see picture). Run a naked piece of cable through, like in the pic, and connect it with the end of the resistor by twisting them together. The twisted parts should be placed in the space outside the plastic skeleton, but inside the cap. The exposed cable on circular aluminum should face the battery that will be placed above.
  • Lay the coin cell on top of the disc. Make an identical aluminum disc that goes above the battery. Cut off a small piece on the edge of the disc for the cable that runs out from the bottom.

Step 7: Run the Wires and Test It

  • Cut out a circular piece of inner tube that will fit snug above the aluminum disc.
  • Connect those two cables (green) with the two ends of another piece of wire (white) that will go through the cap. Just twist the ends together and add some tape. To test if your circuit works, touch the two ends of the cable together — the LED should light up.

Step 8: Complete the Casing

  • Make a hole in the middle of the back cap. If possible, make it as big as the cable and similarly shaped. Run the cable through it.
  • Screw the cap tightly. Then, open it and see where the cable has marks from bending. Now, cut a small piece of inner tube (shape shown in the pic), stretch its smaller edge, and wrap it very tightly (clockwise, so when you screw in the cap it will tighten it more) around the cable 1 cm away from the bending mark and hold it there with your finger. Then take the cap and slide it over the inner tube part. This shape of the tube makes it slide more easily through the hole, and as you pull the cable the back part sticks in the hole, giving a waterproof seal.
  • Before you screw in the cap, you want to turn it counterclockwise one and a half rotations so the cables inside won’t twist so much!

Step 9: Build the Sensor

  • Leave the light aside for a moment to start making the sensor.
  • First, cut a piece of a stick. Its width depends on the distance between your sensor and your magnet. If you want to put it on the fork, the distance is small so you need a thinner stick. If you want to place it on the back triangle the distance is greater, so you need a thicker stick.
  • When you find one, cut it a few centimeters longer than your reed switch. Then, drill a hole (big enough so the twisted cable can go through) all the way through the stick, lengthwise, somewhat near the edge.
  • Now, we will use a big piece of the cable (from the same stock we used to go through the cap) . This will connect the light with the sensor. Use needle nose pliers to hold the reed switch so you can twist its end together with one end of the cables (without pliers you will break it instantly). Slide it through the hole in the stick until it comes out the other end. When it does, twist it together with the other end of your cable. For extra security, you can use some tape to stick the two cable inside the holes.P
  • lace the magnet close to the wood. When the wires are connected, the LED should light up.

Step 10: Light Mounting Mechanism, Part 1

  • Take the wire and make a set of loops. Again, needle nose pliers are an essential tool for shaping the wire, especially if it's a rustproof one. Notice the two pieces of wire that hold together the loops. Also an additional bended piece of wire is there for the hook (check the last photos).
  • This step is a bit tricky if the wire is rustproof. But it't not that hard. You can experiment and come up with a better inner tube holder.
  • NOTE: The wire loops shouldn’t extend beyond the height of the cap as I did in the pics. Also, when you complete this step, try the light on the seatpost and bend the loops slightly if the light doesn’t sit nicely. Cut a strip from an inner tube and run it through the loops like a belt. We do it this way so we can adjust it later if we want to strap it on bigger or thinner tubes.

Step 11: Light Mounting Mechanism, Part 2

Make a hook with the wire and strap it on the end of the inner tube

strip. Bend a piece of wire on the folded end and press very hard until the hook is secure

Step 12: Connect the Light to the Sensor

Connect the wire ends with Tamiya connectors (or any other connectors
you like — there are smaller and better-looking connectors on the market than the ones I used) . This connector is your on/off switch for when you don't need the light (i.e. during the day).

Step 13: Install

  • For the sensor to close the circuit every time the wheel spins, we have to put a magnet close to it. I chose a simple, discreet, and effective installation, but if you find a better one, let me know in the comments.
  • Cut a small piece of inner tube and roll the magnet up. Find the point where two spokes meet and wrap the tube and magnet around. Take a small piece of wire and bend it around the tube and two spokes. Turn it around until it's comfortable for you to work on and clamp it down with pliers (as we did for the strap hook). Use scissors to cut off the remaining inner tube. Finally, turn it around until the magnet faces the sensor, and push it down until it is secure.
  • Now, cut a piece of the inner tube and put your sensor inside it. Then fold the excess rubber and put it on the fork or triangle. Use some zip ties (ideally reusable) to hold it in place. Use some more zip ties (don’t use many, just a few on places where the cable changes direction) to route the cable all the way to the seat post. Make sure the cable is discreet: under and behind the frame.
  • Now, strap the light on the seatpost. It’s very easy to hook and unhook it with your nail/finger.