~Tal Pezzuco ~ Senior Capstone Project~
My name is Tal Pezzuco and I am a senior studying electrical engineering at Union College. This webpage is to document my work throughout my capstone project. I would like to thank my advisor Professor James Hedrick for all the help along the way!
~About My Project~
The objective of this project was to design a system that improves a tennis player’s consistency by counting and recording how many balls they hit over the net in a rally. The goal was to have the system powered entirely on harvested radio frequency (RF) energy since tennis courts are usually outdoors not near power sources. The system needed to harvest enough RF energy to be converted to 5-volts DC voltage and 3 milliamperes, which would power a low-powered infrared (PIR) motion sensor. The design also was required to harvest enough energy at a minimum distance of 10 feet. The system design consisted of two half-dipole antennas that served as a transmitter and receiver. The transmitting antenna was connected to a 5-watt handheld VHF radio. The receiving antenna consisted of a matching circuit, a receiving circuit, a storage component, and a PIR sensor load. The matching circuit used an LC lowpass T-circuit to match a 50 input impedance to a 1000 output impedance. The receiving circuit used a quadrupler with a lowpass filter to convert RF to DC. The storage component charged a supercapacitor that was connected to the PIR sensor. Since harvesting RF energy is a fairly new topic, the design required a lot of testing and debugging of the receiver in order to finish with a system that was successfully able to power the motion sensor. Due to the time spent on the receiver, there wasn’t enough time to program microcontrollers to record the number of times the motion sensor counted a ball go over the net and display the results. The finished project was able to harvest more than enough energy to power the motion sensor, so hopefully in the future with more research on RF harvesting systems, the world will be able to use RF to power bigger things, reducing the need for fossil fuels and greenhouse gases.
~My Design Idea~
An overview of my design idea is shown in the diagram below. A transmitter should be able to reflect enough power to a receiver located on the net post in order to power a PIR motion sensor. The receiving circuit should then be able to wirelessly send the information to a cellular device and display it to the user.
The biggest challenge with the design had to do with the receiving circuit. The receiving circuit had to take the transmitted RF signal and turn it into a constant voltage without losing too much power. In order to do this, I used the circuit schematic below.
The RF source is connected to a matching circuit which consists of an LC lowpass filter. The matching circuit is then connected to a quadrupled, which used four 1N21C diodes in parallel with four 1nF capacitors. The signal then goes through a lowpass filter which filters out any unneeded frequencies. The lowpass filter is connected to a storage component, which is a 1F supercapacitor. When a switch is turned on, the energy from the supercapacitor goes to a voltage regulator which then powers the PIR motion sensor. The user can tell when the PIR sensor detects motion because a green LED will light up.