Introduction: Electricity Generating Footwear - Generate Electricity by Walking (Concept)

Did you know that you can produce electricity by just walking? 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.

Google Fair 2014:
This is my entry for Google's 2014 science fair. Please support us by hitting the like and share button on our YouTube video. The contest is YouTube based so getting a fair amount of likes and viewers would help a lot in getting us through the competition.

Thank you guys for the support! The project has qualified for the regional finalist and won a local award in GSF 2014! :D

Development of The Project:
The power generating soles are one of my first concept projects. I started my first prototype last five years ago although it was a very primitive, compared to my current design. My old prototype had two TO-3 plastic spacer sandwiched between two piezo discs. It produces a fair amount of current, enough to charge a Nokia 3310.

5 years later, I came back with the idea of using the sandwiched piezo setup, this time integrated to a charge collector and powerbank. So I thought, why not add 2 more pairs? After all, more is better.

Concept Behind The Project:
Piezoelectricity was present ever since mid-18th century. Piezoelectricity is the electric charge that accumulates in certain solid materials (such as crystals, certain ceramics in response to applied mechanical stress. This sounds familiar! Yes they do, you can actually find those piezo elements in your old/ outdated earphones from the 90's.

Why Not Use Dynamos?
As much as possible, I tried to avoid using dynamos. Yes dynamos produce more electricity but it will feel like you've stuffed a rock in your shoe. Don't forget dynamos will create a lot of noise.

Any Practical Uses?
As funny as it sounds, charging a phone with your shoe isn't really joke. Who knows maybe someday shoe companies like Nike could use these insole generators to power fitness chips (inside shoes) that would sync to your phone wirelessly. This way, you don't have to charge your smart-shoes just to sync them with your phone.

Disclaimer: This is just a little science experiment. It will show you the concept of producing electricity using piezoelectric elements. Don't assume that is close in becoming a product.

GMA News Network/ Channel Coverage:

Step 1: This Project Was/ Will Be Featured In

People told me to post a list of pages/ shows where the project was featured/ aired.


National Television/ TV Shows/ News Channels:

- Jimmy Fallon Tonight Show (Pending)

- ABS-CBN Rated-K Show (June 15)

- GMA News & Unang Hirit

Daily Newspaper (National):

- Manila Bulletin Newpaper (June 18)

Newsletters And Blogs:

- I.F.L. Science Newsletter & FB

- TV5 Interaksyon Newsletter

- Philnews Newsletter

- GMA News Network

- Yahoo Homepage

- Yahoo News PH

- DamnGeeky

- TreeHugger


- Yugatech

- etc...

Step 2: Science Fair Project - Coverage

I'm using Google's science fair format. This is my instructable version. It's written in a less formal manner so that hobbyist could have a better understanding over this topic.

A Question That Bothers Me A Lot:
Why not use traditional renewable energy sources? Yes I know piezoelectricty is not as well develop as of those solar powered devices but as a curious being, I am open to discovering potential energy sources. Yes, footwear generators may sound crazy and ridiculous but there's more than what meets the eye! These thin insole generators have enough power to supply low current devices.
Coal power is the most common energy source used in the Philippines ,also in the world. For the past decade, our country has been tapping to renewable sources of energy although it’s not rendered free and its price continuously changes (Philippine Star, January 2014). Most undeveloped areas, specially provinces, have no access to electricity. For the people who are living in the suburbs, charging a phone or a lamp is a big deal for them

Over the past years, my science experiments were mostly about renewable energy. I started my first science fair experiment when I was in third-grade, it was my first miniature model of a solar car. The receding years of my science fair entries were mostly about wind, solar, hydro and chemical energy.

My goal is to find a new source of renewable energy, something that does not depend on wind, water or sunlight. I did some random research and I came through tons of eco-energy production articles. I told myself, if I'll go with another solar/ wind experiment, there won't be enough innovation by just remaking a project from the internet. Like all scientists, I had to think out of the box.

Questions To Ponder On:
- Does it have enough power to supply electricity for low consumption modules?

- Will it produce enough power to charge USB devices?

- Can it reach the USB standards?

- Can it power a series of LEDs?

Future Practical Applications:
- Supply on-board/ independent power for smarts shoes and clothing.

- Aid outdoorsmen/ hikers, with GPS tracking shoes,in their journey into the vast wilderness.

- Great for areas where electricity is scarce. - Self-powering rescue chips in shoes.

The project is be accomplished by using piezoelectric materials. Piezoelectricity, also called the piezoelectric effect, is the ability of certain materials to generate an alternating current voltage when actuated.Certain ceramics, Rochelle salts, and various other solids exhibit this effect. For example, (Pb[ZrxTi1−x]O3 where,0≤x≤1), also called PZT, will generate measurable electricity when their structure is deformed by about 0.1% of the original dimension(International AAAI Conference on Social Media and Weblogs, 2012). In this project, the generated electricity on a specific time will be recorded and determine if it would be enough to completely charge a Li-ion battery or a high capacity capacitor.

The project is be accomplished by using piezoelectric materials. Piezoelectricity, also called the piezoelectric effect, is the ability of certain materials to generate an alternating current voltage when actuated.Certain ceramics, Rochelle salts, and various other solids exhibit this effect. For example, (Pb[ZrxTi1−x]O3 where,0≤x≤1), also called PZT, will generate measurable electricity when their structure is deformed by about 0.1% of the original dimension(International AAAI Conference on Social Media and Weblogs, 2012). In this project, the generated electricity on a specific time will be recorded and determine if it would be enough to completely charge a Li-ion battery or a high capacity capacitor.

The piezoelectric effect, by which a material generates an electric potential in response to a temperature change, was studied by Carl Linnaeus and Franz Aepinus in the mid-18th century. Drawing on this knowledge, both René Just Haüy and Antoine César Becquerel posited a relationship between mechanical stress and electric charge; however, experiments by both proved inconclusive. The first demonstration of the direct piezoelectric effect was in 1880 by the brothers Pierre Curie and Jacques Curie. They combined their knowledge of pyroelectricity with their understanding of the underlying crystal structures that gave rise to pyroelectricity to predict crystal behavior, and demonstrated the effect using crystals of tourmaline, quartz,topaz, cane sugar, and Rochelle salt (sodium potassium tartrate tetrahydrate). Quartz and Rochelle salt exhibited the most piezoelectricity.

A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated) The Curies, however, did not predict the converse piezoelectric effect. The converse effect was mathematically deduced from fundamental thermodynamic principles by Gabriel Lippmann in 1881. The Curies immediately confirmed the existence of the converse effect, and went on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals. For the next few decades, piezoelectricity remained something of a laboratory curiosity. More work was done to explore and define the crystal structures that exhibited piezoelectricity. This culminated in 1910 with the publication of Woldemar Voigt's Lehrbuch der Kristallphysik (Textbook on Crystal Physics), which described the 20 natural crystal classes capable of piezoelectricity, and rigorously defined the piezoelectric constants using tensor analysis.

Method/ Testing And Redesign:

Please refer to section #3 to section #14


An Arduino development board was used to establish a simple oscillocope setup. It was plugged to the computer, the built-in TTL was used to establish serial communication between the Arduino and PC. A sketch was uploaded, using the Arduino IDE, to monitor the Analog pin where the insole generator was connected. A separate program, called "processing 2.0", was used to monitor the ripple given off by the converted AC►DC output of the generator.

Conclusion/ Report:

The current results showed that the product has potential to charge lithium batteries. Though there are room for improvements, it showed positive signs for it to be further developed. Based from the results, the insole generator has enough power to supply voltage for low powered circuits such as MCUs (Micro Controller Units - ex. ATtiny) and TTL Bluetooth transmitters. I can now say that the product is ready for production and is highly usable for smart clothing/ shoes. Charging USB devices won't suffice just yet, the charging time just isn't ideal.


If a whole insole was to be made with a thin flexible sheet of metal and glazed with double-sided piezoelectric elements then it would probably produce enough power to charge a phone. A standardized opensource 3D printed design will certainly introduce a new energy-production concept to the DIY community. When everyone has access to an opensource project great ideas flourish!

Glossary/ Terms That You Will Encounter:

  • Piezo Electricity - is the ability of certain materials to generate an AC (alternating current) voltage when subjected to mechanical stress or vibration, or to vibrate when subjected to an AC voltage, or both. The most common piezoelectric material is quartz. Certain ceramics, Rochelle salts, and various other solids also exhibit this effect.
  • Actuated - cause a machine to operate/ work/ generate.
  • Piezo - shorthand for piezoelectric
  • AC Current - the flow of electric charge periodically reverses direction. Piezo elements produce these currents.
  • DC Current - the flow of electric charge is only in one direction. Batteries produce these currents
  • Bridge Diode - usually is composed of four rectifier diodes that filter AC currents and turn them into DC currents.
  • Piezo Disc/ Element/ Transducer - they are all the same, it refers to the discrete component that produces current when actuated. They are also known as ceramic transducers and are usually found in outdated pairs of earpiece.

Step 3: The Concept Behind (Understanding the Key Principles)

Step 4: Parts and Materials

Parts/ 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
- 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 5: 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 matter, 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.

Step 6: 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! :)

Step 7: 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.

Step 8: 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.

Step 9: 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.

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.

Step 10: Building a Bridge Diode

Peizoelectric 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.

Just follow the schematic diagram above. Solder the peizo 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.

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.

Step 11: 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 sandwitches) while walking.

Step 12: 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)

Step 13: Installing the Insole

Slip the insole generator between the shoe and the insole.

Step 14: 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 powebank'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.

Step 15: Conclusion/ Results

Step 16: Future Prototypes - Developing Better Ones

Green Design Contest

Third Prize in the
Green Design Contest

Scientific Method Contest

First Prize in the
Scientific Method Contest

Green Electronics Challenge

Runner Up in the
Green Electronics Challenge

Gadget Hacking and Accessories Contest

Participated in the
Gadget Hacking and Accessories Contest

Full Spectrum Laser Contest

Participated in the
Full Spectrum Laser Contest