Are you inspired with
Angelo Casimiro? Wanna make your own Electricity Generating Sneaker.
Instuctables user ASCAS created
this project as a submission to the Google 2014 Science Fair.
ASCAS says, "Here's a little science experiment that will show you a
little secret on making insoles that can charge USB devices! The
challenge is to make a slip-on insole that can produce enough
electricity to charge batteries/USB devices.
Credits :
ASCAS
Parts and Materials:
- Cheap/ Generic USB Powerbank
- Piezoelectric Transducers (6x)
- 1N4007 Rectifier Diodes (4x)
- Hookup Wire (at least 12")
- Old Pair Of Shoes
- Contact Adhesive
Tools & Equipment:
- Digital Multimeter
- Multitool (w/ pliers)
- Rotary Tool
Optional:
- 100nF Mylar Capacitor (for testing)
- Hoop & Loop Fastener (Velcro)
- LED Indicators (for testing)
- Superglue (for fixing wires)
- Smartphone Sport Strap
- 5v Switching Regulator (w/ supercap)
Alternatives: (since not all can afford them)
- PowerBank > Old phone batteries + Recycled 5v Inverter
- Peizo Transducers > A pair of old & outdated earpiece
- Rotary tool > Hot Nail (for melting plastic)
- Multitool > A pair of pliers will do
Step by Step Guide:
1. Measuring Your Sole
Get the size and shape of your shoe's insole then get a
pair of heavy-duty shears/snips and carefully cut the PVC material. The
plate will act as the primary mount of the piezoelectric discs/elements.
Remember: Thickness matters, you need at least 2-5mm. If your
material is too thick, the piezo elements will break due to too much
flexing. If your material is too thin, the piezo element won't bend at
all thus converting less power.
2. Find And Cut An Ideal Material (Sheet/ Plate)
Now surround the PVC plate with three piezo discs. How do
I know where the center is? The "center" that I'm referring to is area
where all the pressure is withdrawn by your foot, your sole.
After getting a fix preview of the setup, get a pencil and trace the
piezo discs. Finally use your compass to draw smaller circles, about 2mm
smaller in radius. The 2mm spacing will act as your margin.
What material should I use?
Based on my design, I needed a plate
that is 2-5mm thick, lightweight, stiff and can endure a lot of flexing.
Metals are too stiff while carbon fiber is too thin. After playing
around with a bunch of materials, I've found out that PVC fits best in
my application.
Were did you get the PVC material?
PVC materials are all around
us. You can find them in your local hardware store but in the form of
pipes. I got mine from our excess supply of PVC pipes when our house was
built. Recycling means free $$$ for me! :)
3.Grinding Holes On PVC Pads
In this step, grinding is required to bore/drill round
holes. Since I don't have large drill bits (as large as the marked
area), I've thought of way to cleanly cut the holes and that's by using
my handy rotary tool.
If you don't have a rotary tool, you can still cleanly cut the
plastic by doing it "the old fashioned way," by heating an iron nail and
melting the plastic.
4.Gluing The Piezoelectric Elements
These piezo discs must endure a lot of flexing since you'll be stepping
on them repeatedly! Never use superglue, if you do, the moment you step
on your insole the piezo discs will snap off the PVC pad. Instead, use
those quick setting "contact adhesives." Their rubbery characteristic
makes them ideal for this project since they stretch whenever they are
bent.
5. Soldering The Piezos Together
Solder all piezo elements together in parallel. Don't
solder them in series because you'll need more current than voltage and
those piezoelectric discs will cancel each other's power output when not
actuated at the same time.
Piezo elements produce AC currents. Unlike DC currents, you can't
just tap in the line. since AC currents are always alternating
polarities. Just like power generators, whether it may be solar or
petrol, you can't just tap directly to the powerlines without aligning
the AC wave's phase otherwise the generator will cancel each other. (Ex.
Negative meets Positive - Positive meets Negative). This infers that
parallel works best for our project.
Improvements:
Through this process of experimentation, I've
realized that even if they are hooked in parallel the piezoelectric
elements can still cancel each other's output off (when not actuated
simultaneously). This leads to conclusion that you'll need to add one
bridge diode per piezo element/ disc.
6. Building A Bridge Diode
Piezoelectric elements produce AC when subjected to
mechanical stress. Unfortunately, USB devices need DC and not-AC. A
bridge diode is required to filter and convert AC to DC.
Schematic:
Just follow the schematic diagram above. Solder the
piezo discs to your bridge diode. Remember AC has no polarity, you can
invert the wires either way. The load (shown as a resistor) represents
your appliance.
Recycling:
CFL bulbs contain electronic ballasts, each ballast
contains at least six to eight rectifier diodes. Those diodes are
compatible with our project. Please be careful in disassembling CFL
bulbs, I'm not liable if any of you get injured.
7. Adding Foams Pushers
Now glue small a small piece of foam on the very center of each piezo
disc. These foams will act as pushers. These foams will squeeze the
piezo discs inwards (like sandwiches) while walking.
8.Observation And Testing
Finally, we are going to test the validity of or theory.
Start by getting a digital-tester and switch it to the 2 digit DC range.
Remember, piezo elements produce a short burst of current the moment
you push them so adding a 100nF capacitor should make the readings much
more readable.
My volt meter displayed:
Pressing By Hand = 15.03 volts (2mA)
Walking By Foot = 18.53 volts (5mA)
Running By Foot = 27.89 volts (11mA)
9. Installing the Insole
Slip the insole generator between the shoe and the insole.
10. Adding a Powerbank + Soldering
The insole generator peaks a voltage of 28 volts, the
current may be small but the voltage is enough to damage the powerbank's
5v charger (circuitry). I won't be using the 7805 since it's quite old
and inefficient. Right now, my insole generator is soldered directly to
my powerbank's lithium battery. It works but it's not completely not
safe. This is just a prototype so expect another Instructable tutorial/
write-up next week.
UPDATE: Say goodbye to the huge bulging powerbanks! I have a newer
version of the project, the powerbank is now integrated with the insole.
I also added a charge collector circuit.
Credits :
ASCAS
