Piezoelectric Disc/ Solar Panel Exploration

Piezoelectric discs are made of a material that generate electricity from pressure. In this Instructable, we'll be going through some experiments with piezoelectric discs to show how it works and its potential applications. These experiments were done over a year from 2019-2020.

View all of the videos here:

• Piezoelectric discs
• Breadboard
• Wires
• Diodes
• LED
• Mat/strong paper
• Shoe pad
• Wood tiles
• Caulk, small erasers, small wood blocks, or other small objects
• Big wood tiles
• Self adhesive bumpers (the spacer, not the car part)
• Voltage measurer
• LiPo fuel gauge (optional)
• LiPo battery (optional)
• LCD display (optional)
• Croissant box
• Hose
• Flexible solar panel (optional)
• Solder

Wire a circuit according to the image.

Make sure the diodes in the back are in the right place. If the wire ends with the diodes are labeled 1, 2, 3, and 4 (from left to right), there should be a diode from 3 to 4, a diode from 2 to 4, a diode from 1 to 2, and a diode from 1 to 3.

This system of diodes is called a diode rectifier. This is necessary because a piezoelectric disc produces AC current. However, the LED requires DC current, so you need to build a diode rectifier.

Experiment with tapping the piezoelectric disc. The LED should briefly light up every time you tap it.

Also experiment with other types of movement. For example, I tried using a flexible ruler to make the piezoelectric disc vibrate.

This proof of concept steps shows that we can generate electricity with piezoelectric discs. I also learned that I need to use rectifier in the circuit as shown above.

Knowing that we can generate electricity, my first thought is that we might be able to generate electricity while walking, running or perform other exercises. This sounds like a sustainable and green energy source!

Tape 10 piezo discs onto a mat roughly to the shape of my foot.

Wind all of the black wires around to the black wire of the voltage measurer, and all the red wires around the red wire of the voltage measurer. Experiment with stepping on the mat. Currently the circuit has no rectifier and power generated seems very unstable.

Transfer or redo the system on a piece of foam cut into a foot shape with the intention of fitting it into the shoe.

Group all of the red wires together and tape them to a single red long wire. Repeat with all the black wires and a long black wire. Connect the red and black wires to the LED circuit in Pt. 1 with rectifier. This creates more stable outflow of electricity that can light up LED.

We found out that the elasticity of the foam shoe pad was not good enough so we are experimenting with different materials. One of the materials we tried works best is combination of flexible plastic (cabinet protector sheet with dots) with real bouncy shoe pad.

The picture shows tracing on flexible plastic around a shoe sole and cut it out.

Add the piezoelectric discs to the flexible plastic as distributed. We tried different distributions and this seems to be the most efficient pattern.

Step on the foam pad to test how it works.

Use medical tape to secure the LED circuit board to the tester's leg. Take it for a test run!

Results: It kind of worked but will not be practical. The LED will light up but the shoe pad broke very easily. Maybe it can work with an improved manufacture system but I personally do not have.

Next thought is that if the system is so vulnerable on shoe, maybe instead we can put the system of a floor which is more stable? So my next attempt is a floor tile system.

(I did not give up improving my shoe idea though. I later came back with a better version with charging system that can charge a lipo battery, which in turn can power a LED string light laced into the shoe. )

I have no idea what is the best material to tap on the piezo discs, so I decide to try different materials. I used a bunch of 3x3 wood coaster for my prototype.

Divide the wood tiles into a 3x3 grid. Drill holes in each corner. Divide all the tiles into 2 groups, tops and bottoms.

Add the pins and springs on the corners. Glue the piezoelectric discs on the tiles, 1 in each grid square. Repeat for all the bottom tiles.

Put some small sample of a material in each of the grid squares for the tops. Experiment with small bumps materials of different hardness: We used caulk, erasers, and wood blocks.

Press the tops onto the bottoms so that the piezo discs and the bumps meet. Secure with a nut on the top.

Connect the wires to the LED circuit in pt. 1. Try pressing gently or hardly on the tile.

Erasers seems to work best so we decide to use something with similar hardness in our next step.

Now that the small tiles have worked, we can move on to bigger ones. Divide the big wood tile into 64 squares, or as many as you can fit. Place a bumper on each square. Bumper is similar to erasers in our previous experiment that produce best results.

Glue the piezoelectric discs to the other tile. Experiment with different configurations.

Drill holes and place the pins and springs in like with the smaller tiles.

Make sure to use diode rectifiers. We later learned that we needed a diode rectifier for each of the individual piezo discs, otherwise the AC of many piezoelectric discs would actually cancel out.

The diode rectifiers made of four diodes make a diamond, with all the diodes pointing right. The black and red wires connect to the sides (where 1 diode points to the wire and the other points away) and the current runs through the other points in the diamond.

We modified sample Lipo Battery meter code to suit our application, and add on the code to use LED displaying the percentage of battery charged.

When the battery is close to "empty, it charges relatively quickly. However, as it crossed 50% ratio, it is getting harder (have to really tap harder and longer) to get it charged.

Results: It's a bit slow, but the piezo discs do charge the LiPo battery! Is it practical? I would say it is hard. Unless it is built stably into something heavy duty like treadmill, it will be tough to be practical.

Hmm, any other way we can use this amazing energy generating feature of piezo discs?

How about rain? Living in Seattle, we have a lot of rains. Maybe we can use the pressure from the rain?

To extend our exploration, we again start with proof of concept experiment with one disc.

Tape a piezo disc to the top of a croissant (Costco!) box. Wire it to a diode rectifier and a voltage measurer.

Arrange the croissant box with the diode rectifier and voltage measurer under the other half of the croissant box (see image). Use a hose to spray the half of the croissant box with the piezo disc. It may help to hold a baking tray or other item between the two halves, so that moisture doesn't fog up the surface and make it hard to see the voltage measurer. Still, it worked!

Experiment with different numbers of piezo discs. Make sure to have a diode rectifier for each piezo disc.

Make sure to test the hose on each number of piezo discs.

Tape the piezo discs to a flexible solar panel next, and experiment with the power generation.

Results: The solar panel generates significantly more power than the piezo discs. However, the piezo discs are still helpful with capturing some energy from rain. And we now have a portable renewable energy pad that works sun or rain.