Piezoelectric transducers convert mechanical vibrations and pressure into electrical pulses. These sensors have a variety of commercial and industrial applications. Usually, however, the pulses generated are used as transmission for sensing vibrations and pressure, not as power. This project is an attempt to find a way to harness human energy given off from walking, that is otherwise wasted, using piezoelectric transducers, and to explore the applications of piezoelectricity as a possible source of power. The goal of this device is to be able to produce enough electricity to charge small portable electronics such as cell phones. This is done in the form of a removable shoe insole. The insole consists of two foam layers with piezoelectric transducers in between, and a band extending from the heel end of the insole that runs upward between the back of the wearer’s foot and the back of the shoe. It just about rises above the top of the shoe, visible enough for a cable to be plugged in. The band contains most of the electronics, including the charging circuit, battery, and USB port. The pressure of a person’s foot pushing down on the insole when placed in a shoe is translated into electrical pulses using the transducers. This generated electricity can then be used to charge a device via the USB port. If there is nothing plugged into the port, the electricity is stored in a battery and can be used later.
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Step 1: Parts List
- Foam shoe insoles
- Piezoelectric transducers
- 4 diodes
- USB charging circuit
- USB to micro-USB cable
- panel voltage display
- shoe (for display purposes)
Step 2: Piezo Transducer Series
The piezoelectric transducers were soldered together in a series circuit. The wire extending from the outer ring of the transducer is the negative end, and the other wire is positive. For each transducer, the negative wire was connected to the positive wire of the next transducer in the series, and the positive connected to the negative. They were soldered together to make a line, with two leads at the end.
Step 3: Diode Rectifier
The diode rectifier was constructed by taking 4 diodes and arranging them in the square formation shown. The leads were then wound together tightly and soldered.
Step 4: Connecting Piezos to the Charging Circuit
The two ends of the piezo series were soldered to the leads of the diodes as shown in the labeled diagram. The LED was also connected to the same leads. The purpose of the LED is that it lights up when pressure is applied to the transducers to show that electricity is being produced. The micro-USB cable was cut and stripped so that it was left with the micro-USB end that had four smaller wires coming out. The pink one and the black one were connected to the diode rectifier. The micro-USB was plugged into the port on the charging circuit.
Step 5: Connecting the Charging Circuit to the Battery
Two wires were soldered to the charging circuit as shown in the picture and connected to the battery. A switch was also connected to the point where the battery was connected. The switch was connected to the digital voltage display which had another wire connected to the other battery point on the charging circuit.
Step 6: Assembling the Insole
The piezo series was sandwiched between two foam insoles. Using a template guide provided in the package, the insoles were cut to a smaller size to fit inside the shoe. The rest of the electronics were mounted on the shoe.
Step 7: Supporting Documentation
Supporting documentation for innovation.