1. Signal Detection and How to Build an Audio Amplifier
Rebecca Laughon1, Derek Sprinz2
Homeschool1, University of Tennessee2
Introduction
Signal detection is a phenomenon witnessed, but not always recognized, in nearly all aspects of everyday life. It’s seen in televisions, radios, video games, and touchscreens, to name a few. However, it’s not all as simple as it may first seem. Oftentimes, signals initially detected are far to small to precisely analyze and observe. A device called an amplifier can remedy this, increasing the size of a signal without altering its other characteristics, like putting an object under a magnifying glass.
Signal amplification as used in signal quantizing and digitizing
Methods
After learning and extensively practicing the fundamentals of circuits and their construction, we put together a draft design of our amplifier In LTspice, ran a simulation on it, and measured the voltages at three different stages to determine if it would function as we wanted it to.
Circuit design draft in LTspice
Voltage measurement results from LTspice simulation
Ultimately, we wanted the amplifier to have an adjustable gain, such that the volume of the sound coming through the speaker could be raised and lowered. This was achieved by replacing the first resistor in the circuit design, labeled R1, with a device called a potentiometer.
Results
After ensuring the functionality of the circuit in LTspice, we then built the actual circuit on a breadboard, as seen in the left photo, and hooked it up to our speaker and signal generator. Strictly speaking, it worked fairly well, but the power op amp we were using to drive current though the speaker was generating a large amount of excess noise. Removing the component and rewiring the others, as seen in the right photo, restored the sound quality. We were able to increase and decrease the volume by adjusting the potentiometer to raise and lower the gain, respectively.
This work was supported primarily by the ERC Program
of the National Science Foundation and DOE under NSF Award number EEC