science

Generate electricity while walking

Have you ever wondered if you could produce electricity just by walking? This article will help you test out this theory. Let’s figure out if we can charge some lithium batteries while walking.

Materials

USB power bank

Piezoelectric transducers (6x)

1N4007 Rectifier diodes (4x)

Hookup wires

Old pair of shoes

Contact Adhesive

Step 1

To get started with this project, you will first need a pair of shoes, take out the shoe’s insole and trace it on a PVC plate, the PVC should be 2-5mm thick. After tracing with the help of some heavy duty shears you can cut out the part that has been traced out. Place your foot over the PVC cut out and trace your heel size around the PVC. This PVC cut out will act as the main mounting base for other elements that will be added.

While there are other materials that can be used PVC is the best as it has just the right amount of stiffness, is lightweight and is somewhat flexible.

Step 2

For this step, carefully place the three piezo discs around on the PVC cut out. Now you will have to mark out the area that withdraws the most pressure from your foot, this is where you will place your discs. One you’ve done this you can take out a pencil and trace the piezo discs.

Next, you will have to use a compass and draw smaller circles into the traced out piezo discs, make sure the circles that are compassed are 2mm smaller than the traced-out circles, this will act as a margin for your project.

Step 3

Now, you will have to drill the small circle compassed, you can achieve this with the help of a handy rotary tool. Using this toll will give it a clean cutout with smooth edges

Step 4

For this step you will need to glue the Piezoelectric elements, to glue them securely you will need some ‘contact adhesives’, make sure to pick one that sets quickly. Avoid using superglue as it won’t hold your elements for a durable period. The rubbery substance of the contact adhesive will bend with and motion put on it hence lasting longer.

Step 5

Now you can begin soldering the piezo elements. Make sure you solder them parallel and not in series as you will need more current than voltage and placing them in series might stop each other’s power output if not activated at the same time. For a more efficient use you can add a bridge diode for each piezo disc.

Step 6

Now you will need a bridge diode. Since piezoelectric elements generates AC when they are exposed to mechanical stress, and a USB devise that will be used needs DC, therefore, the requirement of a bridge diode is necessary to convert AC to DC.  

Use can refer to the above schematic diagram to understand the soldering placements of the piezo disc to the bridge diode.

Step 7

Next, you will need to take out a foam sheet. You will need to cut 2 small squares on the foam sheet, just enough to fit at the centre of the piezo discs. Once you are done cutting the foam into squares you can start gluing them at the centre of the piezo discs, make sure to carefully place them between each of the piezo discs. This foam squares are used because they will act a makeshift pusher, that will squeeze the discs inwards while you are walking.  

Step 8

A project is futile if it does not deliver what it promises, for this step will test out the validity of the project. For this you can use a digital tester, switch the tester to a 2-digit DC range. As the piezo discs tend to generate a short burst of current when pushed, therefore it is better to add a 100nF capacitor to make more readable. For reference, pushing it by hand can produce 15.03 volts, walking may produce around 18.53 volts and running might produce around 27.84 volts. Once you are satisfied with it you can fit generator into your shoe, and then you can place your insole over it. Make sure the generator is between the shoe and the insole.

Step 9

Make a small hole through your shoe for the wire that is connected to the diode to slip through, connect your wire to your power bank's lithium battery, the generator might produce around 28 volts which is enough to the damage the power bank's charger which is around 5 volts, connecting it directly to the battery of the power bank. It works and it is not completely unsafe,

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