Introduction: Make a Bikers LED Light. Flip-flopping.

About: I'm a teacher (physics, grades 7 to 10), Maker and product designer. (Check out full of experiments, projects for Maker Education and kits for Bibberbeests!). Besides that, I write childre…
Bikers are vulnerable at night in traffic. Now, being vulnerable is fine, as long as it can be noticed by others. So what does a biker need to get noticed at night? That's right! Blinking starlight!

Have a look at the video:
If you can't see the video, take a look at it here.

But where I live, you can't leave your bike with cool led-lights on it. The lights will mysteriously disappear in a matter of minutes. So I wanted to make a bike light that:
  • ... you can wear and take with you
  • ... makes you get noticed by the traffic
  • ... is more or less water proof
  • ... makes you considered being cool by others (if you can't be cool wearing the gear you make, then what's the point of making it? ^_^)
This bikers light is made of an inner tube, stuffed with led's, a make-it-blink-circuit and a replaceable battery. Making LED's blink serves a bit more than just being blinky cool: Blinking also saves a _lot_ of energy, because the led's are on only 20% of the time. That makes the battery last 5 times longer compared to led's that are continuously switched on. By using a flip-flop-circuit to make the leds blink, only one 3 Volt battery-cell is needed to make the leds blink for over 15 hours.

Stuffing an inner tube with electronics is a bit like putting a ship into a bottle: It can't be done, unless you know the secret. The secret for stuffing an inner tube is to flip it inside out. Then mount the electronics, and then flip the tube back, with electronics and all.

In the six following steps are over 50 pictures of the making of the Flip-flop-inner-tube-bike-light. Comments are added to most of the pictures. Have fun making your own inner tube bike light!

Step 1: Tools and Materials

Although three pictures are needed to display the tools and materials you need, there's nothing complicated about it. Here you go:


For the inner tube led-array:
  • Inner tube (of a bike. It's going to be a Bike Light, you know)
  • Paper sheet (to take the measure of the bike light's circumference)
  • 8 - 10 leds, 5 mm model (I used to cheapest possible leds (€0,05 a piece), just because I had them around. You might want to choose more efficient leds. If you do, take notice of the desired current through the leds: The circuit can deliver a max of 200 mA for ALL the leds!)
  • 2 x 70 cm (45") of stranded wire, in different colors
  • Silicone gel (to seal the leds in the inner tube)
  • A silver marker
  • Duct tape (of course!)

For the flip-flop circuit:
  • 2 electrolytic capacitators (elco's): 1 x 100 uF, 1 x 22 uF
  • 4 Resistors: 2 x 1 kOhm, 2 x 10 kOhm
  • 3 Transistors: 2 x BC547, 1 x BC557
  • Jumper wire (or just some stranded wire you ripped out of a junkyard PC)
  • Circuit board

For the powersupply:
  • 1 CR2450 cell battery
  • 1 battery clip for the CR2450 model (PCB version! I used a SMD-version, which I had to hack into a PCB version :-s)
  • Switch that can be mounted onto a circuit board.
  • 6 small Tie-raps (to fix the leads between the circuit boards and the led-array)

For the electronics:
  • Soldering iron and solder
  • 3.5 mm drill (0.14")
  • Cutting Pliers
  • Needle nose pliers
  • Stripping pliers
  • Multimeter (just for checking and/or debugging)
  • Third hand
  • Small saw or dremel to cut the circuit board
  • Water proof sanding paper (roughness 300 or higher)

For preparing the inner tube:
  • Punch, 3 to 4 mm (0.12 to 0.16") diameter
  • Scissors
  • A _metal_ ruler (to punch holes into _one_ side of the tube, not both)
  • Pvc tube (1" diam) that is longer than the piece of inner tube you use
  • Some cardboard (to mount the led-array when soldering)
  • To flip the inner tube inside out: a long, thin, stiff rod with a loop or hole on one end :-D Find a name for that tool: Flipping aid? Flip-rod? I used a cross-brace that comes with ikea's GORM racks. Worked like a charm.)

Step 2: Flip That Tube, Part I

See also the comments with the pictures...

Start with taking the measure of the bike light. I wanted to wear it around my upper arm, so I took some paper to get the size. The inner tube is elastic, so the part of tube that fits around my arm should be a bit smaller (5 cm / 2" at least) than the actual circumference of my arm! 

Divide the length of the tube that fits around your arm in two parts:
3/4 will be occupied by the led-array
1/4 will be occupied by the flip-flop-circuit and the battery

Add some extra length for overlap, and some extra length just to be sure. Oversized inner tubes can be cut to the right size easily. Undersized inner tubes can't be rescued!

Stick some ducttape to both sides of the tip, and punch a hole through it.
Stick the cross-brace ("flipping tool") through the inner tube, and fix it with a tie-rap through the holes you just punched.

Now you can flip the tube: By holding the inner tube and pulling back the cross brace, you can pull the inner tube inside out.

When the tube is inside out, wash it clean with water and a little soap.

Step 3: LED Assembly

Now the inner tube is inside-out, you can start stuffing it with the LED-array. This step consists of a number of sub-steps:
  1. - Lay-out the inner tube and punch holes in the inner tube.
  2. - Preparing the leds.
  3. - Soldering the leds.
  4. - Mounting the leds in the inner tube.
1. Lay out and punch holes.
On the strip of paper, distribute the led's over the available space (about 3/4 of the circumference). Mark the spots where the led's will go, and copy these marks onto the inner tube. Drawing on a inner tube is tricky. I used a soft pencil (6B).

Punching holes in the inner tube requires some tact. The holes need to go through _one side_ of the inner tube only. My punch-tool (a sort of "punch-pliers) is not ideal for the job. A separate punch works much better, probably.
Shove a steel ruler into the inner tube, and punch holes of appr. 3.5 mm (0.14"). The leds are a bit bigger, but the inner tube rubber is elastic enough to fit nicely around the leds.

2. Preparing the leds.
The leds need to be connected into a parallel circuit. This means that all the leds' kathodes must be connected with each other, and all the anodes. The kathode is easily recognizable by the flattened side on the rim of the led.
Because the bike light must be flexible and stretchable, the wires connecting the leds' leads must be a bit longer than the space in between the leds.

  • Bend the leds' leads into a split.
  • Using a small needle nose plier, bend little loops in the leads, as close to the bulb as you can get.
  • Cut away the extruding leads.
  • Mount the leds upside down on a cardboard "placeholder". The holes in the placeholder should have the same spacing as the holes in the inner tube appr.

3. Soldering the leds into a parallel circuit
  • Cut 7 pieces of red coated stranded wire of 6 cm long (2.4"). Strip the ends.
    See pic no. 8.
  • Cut 1 piece of red wire of 30 cm (12") ore more. Strip the ends.
  • Connect the wires "pigtail" (Look here for more about soldering and pigtailing).
    See pic no. 9.
  • Solder the pigtail joints.
You should have a loopy, curved wire with 8 tips close to each other, like picture no. 10.
  • Do the same thing with the black wire.
  • Now solder the black wire to the led's cathodes (the side with the flattened rim). Work from left to right if you're right-handed. See pic 11.
  • Then, solder the red wire to the led's anodes. This completes the parallel circuit led-array. See pic 12.
Time to test! Connect the black ending to a battery's - pole, and the red wire to the + side. The leds should light up.

4. Mounting the leds in the inner tube
Stick a piece of 1" pvc tube into the inner tube, so that it stands wide a little (see pic 15)
Push the leds gently into the holes, with the long wires in the direction of the part of inner tube where the circuit board will go.

Now seal the leds on to the inner tube with silicone gel (see pic 16). I used a match stick to push the gel around and under the leds' rim. Take care of this job. Spots you miss can become leaks, when you're biking in the rain!

Let the silicone gel dry for 24 hours before flipping the tube outside-in again (step 4)!

Step 4: Flip It Back: the Ship in the Bottle

Before you start: Did the silicone dry for 24 hours? If not, skip this step and proceed with the next. Return here when you're absolutely positive that the silicone is hardened.

This step is massively similar to step 2: You need to flip back the inner tube, so the leds become visible. The procedure is exactly the same:
  • Stick some ducttape to both sides of the tip, and punch a hole through it.
  • Stick the cross-brace ("flipping tool") through the inner tube, and fix it with a tie-rap through the holes you just punched.
  • Now you can flip the tube: By holding the inner tube and pulling back the cross brace, you can pull the inner tube inside out.
The difference now is that the tube is packed with leds, wire and silicone. So act carefully. Flipping the tube won't be as easy as in step two, but it can be done!

Step 5: Flip-flop the LED's!

Circuit time!

To start with: There are about a hundred billion different ways to blink a led-array. The first proto I made contains a flashing circuit based on a 555 timer chip. It works fine, but needs 6 volts (two battery-cells) to operate properly. I chose this flip-flop eventually to get rid of the second battery. I could have done that using a low-power version of the 555, but I liked the flip-flop too much (The flip-flop circuit is a real classic, kits are often sold as "Led-flasher").

Does the leds really need to flash? No, but you will drain the battery much faster without flashing the leds. The flashing circuit is a real energy-saver, because the leds are on only 20% of the operating time. If you're not comfortable reading circuits or soldering, you may choose to leave the flasher-circuit out, and put a 50 or 100 Ohm resistor in its place. On the other hand:
you don't have to understand the electronics to build it. Just print the pdf-file and do _exactly_ the same as in the pictures. You'll be fine, I'm sure!

Build the flip-flop-circuit:
  • print the pdf with the schematics and example.
  • cut a piece of circuit board of 11 rows by 25 holes. 11 rows is really the max to fit into the tube.
  • Sand the edges of the circuit board. Edges should be really smooth, or they will puncture your tube!
  • Solder the components of the flip-flop onto the circuit board, one by one. I really needed a third hand to get it done properly.
  • When soldering the capacitators, bend the leads so that the caps lie flat on the board.
  • Cut the copper (through and through! read the tip how to check.) on the X-marked spot in the drawing of picture 1. I used a 3.5 mm drill.
  • Mark the spots where the + and - lead from the leds will be connected on the flip-flop-board.
  • Finally, drill the four holes, 3.5 mm drill.
  • Cut two wires, red and black, 15 cm (6") long. Strip the ends and solder the stranded tips.
  • Take both wires together and lead them through the two holes on the side of the board where the BC547 is. Start from the top (green side) of the board -> underneath the board -> through the second hole.
  • Solder the leads. Black wire on the - lead, red wire on the + lead. The + and - lead on the board are the outer two copper strips. Check the circuit-layout to figure out which one is +.
  • TEST THE CIRCUIT! Connect a battery with the + and - leads, and plug the led's leads into the marked holes.
  • Fix the wires through the holes using tie-raps. Pull them as tightly as possible! See picture 6.

Use a camera to check the cutted copper strip. Take a close-up picture of the cutted spot, and zoom in all the way on the camera's display. The cut should be through and through, not leaving a single strand of copper connected to the other side of the hole. See picture 5 in this step.

Build the power-supply board:
  • Cut a piece of circuit board, 11 rows by 12 holes.
  • Mount the batteryclip for the 2450 cell.
  • Mount the switch, either on the + lead of the battery or the - lead.
  • Drill the two holes with the 3.5 mm drill.
  • Mark the spots where the + and - lead from the flip-flop board will be connected to the battery with a black marker.

Connect the two circuit boards:
The + and - lead from the flip-flop board must be connected to the battery-board. It is _critical_ not to confuse the plus and minus-leads! 
  • Take the = and - lead from the flip-flop board and lead them up through the hole on the battery-board.
  • Find the holes on the battery board where the two wires should go.
  • Cut the wires, so that the two circuit board are only 2-3 cm (about 1") away from each other.
  • Strip and solder the leads endings.
  • Solder the + and - wires onto the battery board.
  • Fix the wires on the battery board with a tie-rap through the hole. Pull the tie-rap tight! See pictures 7 and 8.

Connect the flip-flop to the inner tubes' leds:
... the same way as the flip-flop-board and the battery are connected:
  • Flip back the inner tube to the first led of the array, leaving the red and black wire out.
  • Lead the leds' wires down a hole in the flip-flop-board, and up through the other hole.
  • Find the marks on the board where the wires should be connected. Cut the wires just long enough to reach those holes.
  • Solder the wires onto the board.
  • Fix the wires through the holes using tie-raps. Pull tight!
Test it again! All the electronics hardware is build and connected now! You're ALMOST done...

Step 6: Wrap Up! You're Done!

You're almost done, really. All the hard stuff is behind you now. See the pictures in this step for what needs to be done yet:
  • Pull back the inner tube over the circuit boards. Do it gently. Once pulled back, you can wriggle the boards into a comfy spot.
  • Close the bike light by stuffing one end of the tube into the other.
  • Check wether you need to shorten the tube to get the right size. I could loose some rubber only on the "led-side".
  • Close the bike light again and seal the rim with ducttape, all around the tube.
  • Finally, find the switch on the battery-board through the skin. Mark the spot with a silver felttip marker.

That's it, you're done! Congratulations on your very own, self made bike light! If you worked your way all up through here, please make a picture of your light and post it with this Instructable. Cheers!

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