Piezoelectric-Powered Boots
These Piezoelectric powered shoes were my capstone for my B.S. in Physics at Susquehanna University. Piezoelectric disks are in the heel of the shoe and when the user takes a step, the piezodisk converts their mechanical energy into electrical energy, charging a capacitor. This capacitor can then be wired to a phone charger so you can charge your phone as you walk.
I began testing the piezodisks, wiring them in series and parallel and seeing what kinds of voltage spikes I could produce by stepping on them and putting pressure on them. For this trial, I was able to get a spike of 118 Volts from the 6 disks! The only problem was that this is only a voltage spike and not suitable for charging a capacitor.
This was the initial setup for the first circuit I tried experimenting with. The piezodisk is taped onto a metal ruler and is wired to a switched capacitor. When I hit the ruler, the piezodisk takes those vibrations and puts out an electric current charging the capacitor. When the capacitor is charged, the switch can be flipped, lighting an LED. This is displayed in the video below.
The above video is a test being done using a program called Loggerpro. I am testing the disks voltage production again, but this time Loggerpro allows me to graph and plot the voltage output. This video shows how the voltage spikes go positve and then negative and then back to 0. This means we need something to regulate that voltage to make it all positive.
This is what is called a bridge rectifier. It is four diodes wired together so that the incoming voltage from the piezodisk will become all positive instead of fluctuating between positive and negative. This will help consistently charge the capacitor.
With our bridge rectifier wired into the circuit we now test with Loggerpro again, this time seeing what is the best way of hitting the piezodisk so that it charges the capacitor the most efficiently. This time the Loggerpro leads are hooked directly to the capacitor that is being charged by the disks. The video on the left is fast paced hitting of the disks with a ruler and the video on the right is a slow cpr-like style of pressing the disks.
The above video is of the slow presses and then the fast hits side by side to be able to see their comparative graphs better
Bridge rectifiers wired into the final boot design
Here we have the final boot design being tested with 3 different capacitors. The reason we use different capacitors is because a smaller capacitor will charge quicker while a larger capacitor will take longer. From left to right it is a 10µF capacitor, 475µF capacitor, and then a 1000µF capacitor. These capacitors should charge at 0.0822V/s, 0.012V/s, and 0.0057V/s respectively.