U-TENG Based Shoe Lights for Night Running

As a student, I typically find myself working till pretty late, so by the time I have a chance to go out and run, it's already dark outside. For safety, a lot of people use shoe lights --- which is this sort of U-shaped light clip that you hook onto the back of your shoe --- so that cars and other traffic can see you running in the dark. Skipping to a few months ago, I read this article about this paper on an ultra simple fabrication of a triboelectric nanogenerator (U-TENG), and figured that trying to make an U-TENG based shoe light would work pretty well. The faster you walk/run, the more the LED will flash! (It basically automatically flashes when you take a step, which is extra good for visibility!)

*Note* This is very much a WIP, and I'm half throwing this out there to see if anyone has any thoughts for improvements. You have been warned! Now without further ado...

You will need:

1. ITO-PET film (You can get a decent sized sheet for <$20 on Amazon! Didn't know you could buy this...)
2. Kapton tape
3. Wire (I'm using 24 Gauge, but there might be something more optimal)
4. A rectifier (I'm using a KBP307, but you could also build your own diode bridge)
5. An LED (or LEDs. You could theoretically use the LEDs as your diode bridge so that they would alternate flashing when you stepped down and released your foot)
6. Solder & soldering iron
7. Multimeter
8. PCB breadboard
9. A shoe mat (or your foot)
10. More tape for keeping everything together (I used painters' tape here)
11. An insulator to use as a spacer for the U-TENG (The original paper used pieces of glass cut from a microscope slide. I used some pieces of plastic wrapped in painters' tape.)
12. (sort of optional) oscilloscope
13. General tools: Scissors, markers, gloves

Use the multimeter to identify which side of the film is conductive. (Remember to probe under any protective film or else neither side will be conductive. The first photo shows the non-conductive side, and the second photo shows the conductive side.)

Using a shoe mat (or your foot) to trace your heel on the film with the conductive side up, then cut it out. (Tip: keep the protective film on when you do this.) This will be the bottom piece.

Take this piece and cut another piece mirroring it (such that if they were stacked on top of each other, the ITO/conducting sides would be facing the opposite direction). This will be the top piece.

Cut and strip two wires (a few centimeters should do since it only needs to go from the base of you heel to around your ankle).

Apply Kapton tape to the conductive side of the bottom piece. (The protective film should be removed at this point.) Put the end of one of your wires under the tape on the side where your heel would be. (Tip: try to smooth out any air bubbles; I used a card for this, but I've read about using soapy water then letting it dry too?)

Stick one end of the other wire to the conductive side of the heel of the top piece. (I'm using the Kapton tape here, but other methods should work too.)

*Skip this step if you don't have an oscilloscope*

Hook this up to your oscilloscope! When you smack it, you should see a spike in the voltage. (If not, check to see if you have conducting side flipped somewhere.)

Check the attached video for a demo!

Add the spacers to the sides of the U-TENG. Here I wrapped these thin pieces/sticks of plastic in tape as my "spacers", then taped the bottom and top pieces together so that they sandwich the "spacers".

I tested this first on a normal breadboard to see if the circuit worked, then soldered the equivalent on this PCB breadboard. Everything is centered to one side, since you want the top of the PCB to be sticking out of the shoe.

The second photo shows the basic wiring/circuit for the PCB and U-TENG.

Here's an attached video of the LED flickering when the U-TENG is stomped on! If you hit it harder/faster, it will be somewhat brighter.

(Unfortunately, although it technically works, the LED is rather dim and can only be seen clearly in the dark. Since the paper reported making a relatively small U-TENG (3.5 cm×2.75 cm) and stated that the U-TENG could generate sufficient power to power red and green LEDs, I'm not sure why my LED is struggling to light up as brightly. It should be noted that when testing with the oscilloscope, my U-TENG never reached their reported max voltage of over 400V.)

Anyways, that's it! It can be a bit uncomfortable to have the PCB digging into your heel, so I'd recommend using a piece of cloth/a sock to pad the back of your shoe. The U-TENG itself is barely noticeable since it is very thin. Alternatively, you can attach the PCB to the outside of your shoe instead of sticking it inside like this.

I'll probably come back with an update if I can improve the brightness of the LED and make the setup more comfortable. Any feedback/suggestions for this would be appreciated :) Thank you!