Finally, at the end of the semester, I have completed my AM radio not only by constructing it with the necessary components that allow it to function as intended but also by implementing my own ideas to enhance its quality. As evident by the title of this post, I wanted to adapt my radio into a user-friendly device, adding components that give the user easy control over. The main components I added were a 9V rechargeable battery, a power button, a volume control knob, and a OLED display for frequency information.
Shown in Figure 1 to the left, I followed this circuit schematic to construct the fundamental infrastructure of the radio. This design was provided as a recommendation in Lab Manual 5, and it was almost identical to the design I had at the time. So I took this circuit as my starting point and began to integrate the components mentioned above.
First, I decided to use a lithium ion battery (Figure 2) for two main reason: long battery life and portability. When I use the word portability, I do not mean that I would take this radio on vacation with me because that would be very impractical. I just mean that the battery allows me to easily transport the radio from my kitchen table (where I keep it when I want to listen to it) to the desk in my room (where I tinkered on it). Also, because of the circuit's very low current draw, the battery lasts for hours (that means hours of ESPN radio!).
In addition, I added an LED-illuminated power button (Figure 3) for easy on/off functionality. This was very useful when tweaking the radio because it saved me time from disconnecting and reconnected the battery terminals. Although the button has multiple wires, Figure 4 shows a simplified version of the wiring diagram, specifically highlighting the basic function of acting as a switch for the power to the radio.
Likewise, I integrated a volume control knob using a linear 10 kilo-Ohm potentiometer for convenience. This was extremely useful when adjusting the antenna because the awful noise coming from the speaker was so loud. On the downside, the potentiometer's resistance is so large that the full knob cannot be utilized.
Finally, I integrated an OLED display utilizing an Arduino Uno Rev3 microcontroller (Figure 5). This idea originated from a failed attempt to read use the Arduino to read the input frequency into the radio and display its recordings. However, because I do not intend on ever changing the station (forever listening to ESPN Radio), I simply wrote code on the Arduino, which is also powered by the same button, to display the frequency at which I have tuned my radio: 1.23 MHz. Consequently, however, the Arduino also introduced more noise to the radio. Interestingly enough, I found that if I disconnected the antenna and held the OLED display near the antenna input, I could hear the I2C clock from the Arduino to the OLED in the speaker. This was undesirable but very unnoticeable when the antenna is connected.
Despite these additions, the radio still has some problems -- functionality issues because of the antenna and grounding issues. First, the radio will indeed pick up the intended station, but there is much noise. This is solely due to the antenna and I have verified this by propagating a sine wave from a function generator through the radio and listening to the crystal clear hum (video below). As I tinkered with my device, I discovered that my pizza box square loop antenna is acutely sensitive to the slightest changes in orientation. This made it almost impossible to consistently listen to the radio as it was difficult to maintain the necessary orientation. It is also very sensitive to position. At my home in Auburn, sometimes I could pickup the station and listen to very faint broadcasts. In the electronics lab at Auburn University, I could listen to ESPN radio crystal clear (video below). Furthermore, because of the low quality of the electrical components I am using, some components were not well grounded, which introduced more noise into the system. As can be seen in one of the videos below, to function properly, the circuit required that someone push down on the top of a capacitor. Nevertheless, in spite of these issues, I still enjoy turning on the radio and listening to the glorious sounds of ESPN radio.
Arriving at the end of a semester long project, I can now look back to the step-by-step process of constructing this device and make some conclusions. First, as much as I am in awe of such an engineering feat for a college student, this is not a reliable device at all. Its volatility at times was very frustrating when all of a sudden it stopped working completely. Most of the time, these sudden failures were unexplainable and could not be resolved. However, even if I did not make any changes, it always eventually functioned properly. Second, I have concluded that I thoroughly enjoy seeing the works of my hands behave as intended. It was a great delight to turn on the radio that I had built and listen to a few innings of the World Series at home. Last, the information and experience that I have gained in this course has provided me with ideas and inspiration for more electronics projects which I look forward to. With an understanding of the basic behavior of RF devices, I have a new field in which I can work and explore. At the end of this project, I am grateful for the opportunity to learn and build an AM radio and thrilled to achieve such an accomplishment.
Enjoy these videos and pictures of the final product:
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