In 2014, Angelo Casimiro, a 15-year-old student from the Philippines, drew international attention for a shoe insole that produces electricity as you walk. His device uses piezoelectric discs, small components that release a burst of electric charge each time they are squeezed, tucked under the sole so that every step presses them. He entered the project in the Google Science Fair, where it was reported to have reached the regional finalist stage, and he published his build openly so anyone could copy and improve it.
The idea is genuinely clever, and it is also a good lesson in how much energy a footstep can realistically deliver. Here is how the insole works, what it can and cannot power, and where this kind of technology has gone since.
Who is Angelo Casimiro?
Casimiro was a teenager with a long-running interest in electronics. According to reports at the time, he had been tinkering with the idea of capturing energy from walking for around four years, since he was about 11. Rather than keeping the design to himself, he documented it on Instructables, a community website where makers share step-by-step projects, under the title "Electricity Generating Footwear". He described it as a concept: a slip-on insole meant to collect enough energy to charge small USB devices.
The Google Science Fair, which ran from 2011 to 2018, was an online competition for students aged 13 to 18 around the world. Projects were judged in stages, with regional finalists chosen before the global finalists who travelled to Google's headquarters. Casimiro did not win the 2014 top prize, which went to three Irish students for work on bacteria that help cereal crops grow, but his project became one of the most widely shared entries of that year.
In the video above, Casimiro explains his project in his own words and demonstrates the insole.
How a piezoelectric insole works
Piezoelectric materials turn mechanical stress into electricity. When certain crystals and ceramics are bent or compressed, the arrangement of charges inside them shifts and a small voltage appears across the material. Release the pressure and the voltage reverses. Common examples include quartz, Rochelle salt and the ceramic lead zirconate titanate, often called PZT, which is used in the cheap buzzer discs found in many gadgets.
In a walking insole, the basic chain looks like this:
- Pressure: your heel strikes the ground and squeezes the piezo discs beneath it.
- Alternating voltage: each press and release produces a quick pulse that swings positive and negative.
- Rectifier: a bridge rectifier converts those swings into current flowing one way.
- Storage: the energy is collected in a capacitor or a small rechargeable battery.
- Output: once enough energy has built up, it can feed a low-power device through a USB connection or similar.
Casimiro's write-up walked readers through building exactly this kind of circuit, which is a large part of why it was popular with hobbyists and teachers.
The whole system is meant to fit inside an ordinary shoe, so the wearer does nothing different: walking alone does the work.
A quick correction on the history of piezoelectricity
In his project notes, Casimiro wrote that piezoelectricity had been known since the mid-18th century. That is a small but common mix-up. The direct piezoelectric effect was first demonstrated in 1880 by the French brothers Pierre and Jacques Curie. What scientists such as Carl Linnaeus and Franz Aepinus studied in the mid-1700s was a related effect, pyroelectricity, in which some crystals produce a voltage when they are heated or cooled. The two are cousins, and it is easy to see how they get blended together.
Can walking really charge your phone?
This is where early headlines ran ahead of the physics. Stories at the time suggested the insole could end phone-charging worries on holidays or hikes. In practice, piezoelectric harvesters produce very little power. Reviews of energy harvesting put typical output from human-motion devices in the range of microwatts to a few milliwatts. A modern smartphone battery stores several watt-hours, so topping it up from footsteps alone would take an enormous amount of walking.
The challenge is not just Casimiro's. The US defence research agency DARPA once funded work on boots that would harvest one to two watts from soldiers' footsteps to power field equipment. The effort was eventually dropped because getting that much energy out of a shoe made it impractical and uncomfortable to wear. Pressing harder on a generator means the walker is doing extra work, and that is felt with every step.
Casimiro himself was careful on this point: he described his insole as working but not yet ready for mass production. Seen that way, the project is a success. It proves the principle, shows a full working circuit and gives others a starting point.
A useful habit when reading about any student invention, or any energy gadget, is to ask for the energy figure rather than just a voltage reading. A brief spike of several volts sounds impressive, but what matters for charging is how much energy is delivered over time. We looked at the same question in another young inventor's project, Hannah Herbst's ocean-energy prototype.
Where footstep energy is actually useful
Although phone charging from shoes remains impractical, harvesting energy from movement has found real niches:
- Low-power sensors. A few milliwatts is plenty for a step counter, a temperature sensor or a small wireless transmitter. Researchers have explored shoes that power their own tracking electronics.
- Busy floors. Piezoelectric tiles have been tested in train stations and on dance floors, where thousands of footsteps add up to enough energy for lighting or displays.
- Battery-free switches. The same principle lights some gas stoves and powers certain wireless light switches, where a single press supplies enough energy for one signal.
The common thread is that piezoelectric harvesting shines where devices need tiny amounts of power and changing batteries is a nuisance.
Why the project still matters
Casimiro's insole is a good reminder that teenage science is valuable even when it does not change the world overnight. He picked a real problem, learned the physics, built a working prototype, tested it, and then shared everything openly. That last step, publishing the design for anyone to use, is what turns a single science-fair entry into something that can keep teaching people years later.
If you want to try it yourself, piezo discs, a bridge rectifier and a small capacitor are inexpensive and widely available. It makes an excellent school or weekend project, as long as you expect to light an LED or charge a capacitor rather than fill a phone battery.
(The video originally embedded here is no longer available on YouTube.)
Sources: Angelo Casimiro: Electricity Generating Footwear (Instructables); Wikipedia: Piezoelectricity; Wikipedia: Energy harvesting; Wikipedia: Google Science Fair. Story first circulated via True Activist and The Mind Unleashed.
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