FM Radio

Hi! My name is Mia and I am a rising sophomore at SAR High School. For my starter project, I built a MintyBoost, which is a battery powered portable charger for your cell phone or any other device that connects through a USB cable. Then, for my main project, I constructed a monophonic Frequency Modulation (FM) receiver that accepts FM signals in the frequency range 88-108 MHz. I chose both of these projects because they would give me a hands on introduction to engineering and increase my knowledge of the electronic parts on a circuit board, such as resistors, capacitors, transistors, semiconductors, and more. 

Engineer

Mia G

Area of Interest

Electrical and Mechanical Engineering

 

School

SAR High School

Grade

Rising Sophmore

Reflections

I enrolled in the Blue Stamp Engineering Program to gain a deeper understanding of engineering and project building and, over the course of my two weeks at this program, not only did I build two projects independently, but I was also able to explore different engineering tools, parts, and practices. Before even walking into the first day of class, I learned the importance of project planning and research by creating my Bill of Materials and my Build Plan. This skill was important when I came across design problems in the project building stage because it allowed me to look back on my work and see how I could change my approach to avoid mistakes. I strengthened my critical thinking and troubleshooting skills and I was able to invent creative solutions to the technical issues I faced. The Blue Stamp Engineering Program offered me an environment that allowed me to thrive and flourish. Instructors were welcoming and available to assist, but they also encouraged me to think of unique solutions on my own. I felt confident knowing that I had a team supporting me and I was learning the skills to overcome obstacles. This has given me the confidence and the motivation I need to start building more sophisticated and complex projects and to begin designing new modifications to personalize my projects. It was really helpful to document my work along the way by writing in my project notebook, recording videos, and creating my own website because it improved my communication and writing skills. I want to be able to share my ideas with other students and hopefully influence students to involve themselves in engineering, just like I did. This experience and my exposure to the different fields in engineering has really been very beneficial and memorable. I have never participated in a program like this and in doing so, I acquired many skills that will serve an important purpose in my life and hopefully for years to come. The program was also very fun! Each problem I faced was a challenge, but the complications allowed me to grow and use my problem solving skills to find a solution. Engineers are constantly changing the world with new ideas and innovations and I am happy to be a part of that! I am very proud of what I achieved so far and I am looking forward to gaining more experience and expanding on my skills in mechanical, technological, mathematical, and scientific fields. Engineering is something I am very passionate about and I can’t wait to continue learning!

Final Milestone

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For my third and final milestone, I incorporated all of the modifications into my FM radio and acrylic plexiglass showcase housing including my 3D printed personalized knob and my copper tape paper speaker. I made careful measurements when designing my 3D knob to ensure that it would easily fit over the knob on the potentiometer and stay secure. After my knob was printed, I slid it over the top of the knob on the potentiometer and it fit perfectly! Now, my knob is conveniently placed to make it accessible and allow for comfortable volume and power control.  To make my speaker, I cut a piece of printer paper into a square and I used copper tape to form thin circular coils on the front side of the sheet of paper. A continuous spiral coil shape provides the loudest and clearest audio. Each time a segment of copper tape ripped or pieces of tape overlapped, I would solder the gap to create a connection and restore the continuity throughout the circuit. After I checked that all the components were properly soldered together, I attached two alligator clips to the ends of the copper tape. I attached the other end of the alligator clip to a 60 watt amplifier. After placing 4 thin neodymium magnets on top of the speaker, the music started to play out of my diy speaker!! The speaker can also be attached to play audio signals from an FM radio, like the one I built, or other electrical devices, such as a cell phone or computer, using an aux cord. The way the speaker works is that the copper tape that is mounted on the thin paper surface carries audio frequency currents. When current is passed through the coils, an electromagnetic field is created. Since there is a permanent magnet placed near the electromagnetic field, the magnets either repel or attract each other when they come into contact, depending on which signal and pole is present. Due to this interaction, the two magnets vibrate to create sound and act as a speaker. The larger and stronger the magnet, the more sound will be produced. Before creating this speaker, I constructed a different speaker using a plastic cup, copper wire, packing tape, and neodymium magnets, but unfortunately, it didn’t amplify sound like I had hoped. It took many trials and errors to decide on this working design with copper tape. Although the speaker isn’t very powerful, it was interesting to experiment with speaker modeling techniques and different circuit designs.

Second Milestone

For my second milestone,  I completed my first modification, which was designing an acrylic plexiglass showcase for the housing of my radio. One of the challenges I encountered was developing a design that would allow the radio to be secure in a protective framework while also allowing the switches and knobs of the radio to be viewable and accessible from the outside. I also had to create a way for the sound to travel out of the radio. After marking the plexiglass with a thin sharpie and lining up my ruler along the plexiglass using alligator clips, I worked with many tools, such as a plastic cutter tool with a sharp steel blade and a dremel, to cut the two pieces of plexiglass I needed for the front and back of my showcase. Using the dremel allowed me to quickly and efficiently cut clean straight lines in the plexiglass, while the cutter was much more time consuming and required a greater amount of force. I would recommend using a dremel when recreating this project. I sanded down the edges of the plexiglass using sandpaper and files to make them smooth and sleek. I took a drill and, lining up my front and back sheets, I created four holes to insert standoffs so that there would be room for me to place the radio in between the two pieces of plexiglass. I drilled three additional holes in my radio, making sure not to interrupt the circuit, and then I made those same holes on the back sheet of plexiglass. I used more standoffs to mount my radio in between the two sheets of plexiglass so it would not fall down through the bottom. After, I drilled a circular hole for the knob and a rectangular hole for the two push button switches so that they would be accessible from the front of the radio. I filed the holes to get rid of the jagged edges and make the insertions polished. Then, I stepped back and admired the smooth finish and clear viewing of my radio in the showcase. I came across a few complications during this process, such as creating some scratches in my plexiglass, damaging a few pieces of plexiglass, and making uneven holes with the drill, but I was able to overcome all of these obstacles. Another difficulty I faced was that the knob on the potentiometer, which turns on the radio and adjusts the volume, was too short and small to be reached from the outside. I am in the process of modeling a 3D printed knob to act as a replacement for the knob on the potentiometer to expose the dial and make it usable. I am adding my name on the dial as a personal touch to make my radio unique. Overall, I am happy with my final project and the new skills I acquired.

First Milestone

For my first milestone, I finished building my radio by installing all of the electronic parts to the PC board and testing my radio to make sure it functions correctly. This monophonic Frequency Modulation (FM) receiver accepts FM signals in the frequency range 88-108 MHz. This FM radio uses an electronic auto- scan to search for FM stations and it is operated by two push button switches. The two switches are scan “S” and reset “R.” The circuit contains two ICs (one for the audio section and one for the radio frequency), a 9V battery as the power source, an antenna to radiate and pull signals, an 8Ω speaker to give off audio, a potentiometer to control volume, and a few other components. I started by soldering various resistors, capacitors, semiconductors, and coils to the PC board. Resistors, such as the 50kΩ (Ohms) Potentiometer, are electronic components that resist the flow of electricity. Capacitors, both discaps and electrolytic radials, are electronic components that store current and block the direct current, which only flows in one direction. Diodes are electrolytic components that change alternating current and direct current. A varactor is a diode that changes its internal capacitance depending on the applied voltage. Coils, such as 4-turn coils and 6-turn coils, have inductive reactance, which is what an inductors electrical resistance is called when used in an alternating current circuit. They receive and transmit radio frequency signals. Next, I mounted my red LED to the PC board, which is a diode that gives off light when voltage and current are passed through it. I attached my IC socket and inserted my IC chip into the socket. This IC is an LM386 amplifier, a low voltage audio power amplifier. In order to make the amplifier more versatile, two pins are provided for gain control and adjustments. 1.35kΩ resistors set the gain at 20 when pins 1 and 8 are open, but the gain can go up to 200 if a capacitor bypasses the 1.35kΩ internal resistors when it is placed in between pins 1 and 8 . The amount of gain control, or signal multiplication, changes based on the potentiometer which varies audio level and volume. I installed my battery holder and speaker and soldered the speaker wire to the pads +SP and -SP. To test my radio, I installed a new 9V battery in the battery holder, extended my antenna, turned the power switch on the potentiometer to on, and turned the knob fully clockwise. The LED lit! Next, I pressed the reset button and the scan button a couple of times until I heard a station. Pressing the scan button allows you to search for other broadcasting stations. The tuning on the radio is done using a varactor diode and the varactor capacitance is changed by altering the DC voltage supplied to its anode over resistor 3. Station signals are led from the telescopic antenna to the input circuit and inside the IC, signals are led into a mixer. There they are given a new carrier intermediate frequency. The IF amplifier only amplifies one of these signals: the one whose frequency is equal to the IC. Then follows the limiter, demodulator, mute control circuit, and pre audio amplifier, which all affect the sound and the frequency of signals. Some problems I faced were that when I first turned on my radio, I didn’t hear any sound. After checking the position of the parts, the solder joints, the voltage, and the continuity, I discovered that the problem was that the IC chip for the audio section of my radio was dead. I needed to order a new LM386 and desolder my old IC socket in order to fix this problem. Another problem I faced was that I had trouble soldering one of my parts and I lost the connection on the PC board when I burnt off the solder joint and socket. I had to attach an extra wire along the top of two solder joints in order to restore the continuity. The sound wasn’t clear when I turned on my radio, so I installed capacitor C* onto the copper side of the PC board on top of the radio frequency IC to improve the sound. I added an extra capacitor because a capacitor blocks all direct current and passes only alternating current, a type of electrical current that continuously changes direction, including audio. Capacitors can take up, store, and release electrical energy fairly quickly so they are used to filter any abrupt changes in circuit voltage and filter out high frequency noises, which smooths the signals.There are many differences between AM, Amplitude Modulation, and FM, Frequency Modulation, radios. AM signals vary their amplitude to adapt to the sound information that is transmitted through the wavelengths, and these changes are very noticeable because they result in audible static. In an FM radio, sound is transmitted through changes in frequency and changes in amplitude are much less noticeable. When you switch between broadcasts on an FM radio, the antenna is switching between different frequencies and amplitudes which produces better sound and less static in transitions. I was so happy that, despite a few complications, I successfully completed my radio!

Starter Project

My starter project is the MintyBoost, a portable backup charger for your cell phone or any other device that uses a USB cable. The power source is two AA batteries, which each provide 1.5V. I began by soldering 5 resistors, 4 capacitors, and a diode onto a circuit board. The resistors are nonpolar and are used to restrict the flow of electrons through the circuit which limits the current and they also identify which device is being charged.  There are two types of capacitors. The ceramic capacitors are non polarized and they stabilize the chip to keep a steady current if the voltage changes and they filter out high frequency noise. The electrolytic capacitors are polarized and are used to store charge because they can hold a lot of charge in their strong electromagnetic fields. The diode is used to make sure energy is transferred one way: from the batteries to the USB port. I also attached an IC socket over the chip to protect it and to allow me to replace the chip if any problems occur. The power inductor L1 is used by the DC/ DC converter chip to store and convert power from low to high voltage. I then inserted a converter chip which accepts an input source voltage between 1.2 V and 14 V and converts it into a regulated output voltage and limits the current. It contains at least two semiconductors, a diode and a transistor, and at least one energy storage element such as a capacitor, inductor, or both. It also has filters made of capacitors on the input and output. The boost converter chip uses a type of switch, such a transistor, to turn a part of the circuit on and off at a really fast speed when power is supplied. When you turn it on, current can flow from the power supply through the inductor through the switch and back to the power supply. As you turn it on and the current flows through the inductor, a magnetic field builds up in the inductor. When you turn the switch off, current can no longer flow from the inductor through to the switch because the magnetic field in this inductor has collapsed. The inductor needs to induce current through the circuit but current can no longer flow through the switch when it is off. Instead, the current quickly flows through the rest of the circuit. The collapsed magnetic field of the inductor creates a high voltage spike and the charge is pushed through the diode and stored in the capacitor. This adds to the voltage of the capacitor and steps up the voltage. The inductors polarity on the right side is usually negative and on the left side is usually positive, but as we supply voltage to the inductor when switch is off, the polarity changes and the right side is positive and the left side is negative. This allows the current to flow to the rest of the circuit because positive is connected to positive. This converter chip converts the 3V from the 2 AA batteries into the 5V necessary for charging a USB device. I used a multimeter to measure the voltage in the pins of the USB connector. I attached a USB type A connecter which nearly all USB charger cables will plug into. Lastly, I inserted my batteries and circuit board into a tin, securing them with a small piece of double sided tape, and tested my portable charger. I was successful! Although it took some time, I was pleased to acquire new skills and complete all the steps correctly to create a working portable charger.

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