ELEC 3030 Final Project
Music Equalizer
My group members and I decided to enhance our radio by being able to control volume, bass boost and treble boost. In order to achieve this objective we bought two 100k ohms linear potentiometers to control bass and treble boost. To control volume we decided to buy one 500k ohms logarithmic potentiometer. We had the idea that if we could control these three factors that we could reduce/eliminate noise and create a better quality sound. In order to measure volume, bass and treble we used the oscilloscope and RF spectrum feature.
Plan
First Radio Design
When we first started this project our radio was outputting a strange signal and the results were not pretty. After testing each part individually we figured out there was a problem with the CE-CC audio amplifier.
New Radio
Once we figured out that the problem was with the CE-CC amplifier, as a group we decided to go with the LM386 op-amp. After doing more research it turned out that the LM386 op-amp worked better as an audio amplifier in the sense of our project. Shown on the right is the newly updated schematic for our radio.
Budget
This was our projected budget for our project. We actually were under budget because we only spent 8 dollars instead of 15 dollars.
Theory
Potentiometers
The way potentiometers work is that they put more or less resistance into the circuit. A potentiometer has three parts to it, ground, output and Vcc+. In the figure shown to the left, it displays that if you move the knob left you are adding more resistance and if you move the knob right, you are adding less resistance. You can use a potentiometer in two ways, a variable resistor or a voltage divider. When using a potentiomater as a variable resistor you only use output and Vcc+. When using a potentiometer as a voltage divider you use ground, output and Vcc+. As a group decision we decided to use the potentiometer as a variable resistor.
Linear vs. Logarithmic
Our group also had to make another decision regarding the potentiometers. The two different potentiometers are linear and logarithmic. For the bass and treble boost we used a linear potentiometer. For volume control we used a logarithmic potentiometer. The reason we used logarithmic potentiometer instead of linear for volume control is because we wanted a gradually change.
LM386 op-amp Pin Layout
In the figure shown to the left you can see which pins we connected each potentiometer to. The volume potentiometer was placed in between the output of the AM detector and pin 3. The gain potentiometer was placed in between pin 1 and 8. The bass boost potentiometer was placed in between pin 1 and Vout.
Issues
Potentiometer Problem
One issue that our group ran into was connecting the potentiometer to the wrong pins. A diagram of a logarithmic potentiometer is shown to the left. The reason we were connecting the volume control to the wrong pins is because +Vcc and ground are swapped in a linear potentiometer.
Resistor Problem
The second issue that our group ran into was a resistor was burning. At first we could not figure out were the burning smell was coming from but we soon came to realize it was the resistor connected from Vs to the ground. To fix the issue we removed the resistor as a fire hazard.
Equipment Problem
The third issue depended on the day because you never knew if our group was going to get bad or good alligator clips. For example we were getting very good results on the oscilloscope but we forgot to take screenshots which came back to hurt us. The next day that we were back in lab we were able to get relatively good results but they were not comparable.
Results
Volume Control
In the figure shown to the left the output has an amplitude of 832mV. The figure shown to the right, the output has an amplitude of 680mV. What these two figures show is when we added more resistance the amplitude went down. Hence it shows that our volume control is working. Its not shown but when we turned the knob to the highest resistance the amplitude was at 0 volts.
No Bass or Gain Boost
The figure shown on the left shows the RF spectrum when the tuner potentiometers are at 0. This figure is mainly a reference figure for the other results. In order to demonstrate bass and treble boost we connected an aux input to our radio and played music from our phones to get a better range of frequencies.
Bass Boost
In the figure to the left it shows bass boost. The bass boost potentiometer works as a low-pass filter, it passes low frequencies and removes the high frequencies. The low frequencies are on the left of the plot and the high frequencies are on the right of the plot.
Gain Boost (Treble Boost)
Treble boost was our downfall of this project because we did not get it to work. As a group we thought that gain boost would act as a high pass filter and remove the low frequencies while passing the high frequencies. Instead gain boost just increased both.
Reflective Writing
This project was very eye opening. I learned how to project a budget and experiment with designing my own project. I did not realize what was actually happening was I was affecting the bass and volume in my car radio. It has definitely been one of the more interesting things I have done since I have been in college. This lab and final project has me excited for the things to come and the future labs.