Lab Report 4

Experiment

Our class was tasked with creating a low pass filter and a high pass filter using a variable resistor and a capacitor. It turns out the solution was fairly simple, and you just needed to have either component bypassing the signal to ground to create the filter effect.

Here are some pictures of the circuits

Low Pass Filter (Resistor - Capacitor to Ground)

I used a 1 microfarad capacitor. The range of the corner frequency when using a 1 microfarad capacitor and a 10 kOhm variable resistor starts at (1/[(2*pi)(1*10^-6)(10000)]), and ends at (1/[(2*pi)(1*10^-6)(1)]). Starts at 15.9 Hz, and ends at 15.9 kHz.

High Pass Filter ( Capacitor - Resistor to Ground)

Since the resistance and capacitance values are the same as the first circuit, the range of corner frequencies is also the same, only the effect of the filter at these frequencies is reversed.
However, I didn't really hear that significant of an effect until the corner frequency was either very high or very low, so these ranges are probably more theoretical than practical.

Questions

1. Since we're using a variable resistor with a set range of resistance, the upper corner frequency depends entirely on the capacitance. So if the upper range of human hearing is 20 kHz, you would need a capacitor with a capacitance of {20000 = 1/[(2pi)*c*1]}, or 7.9 microfarads.

2. Once again, you would have to change the capacitance, but this time you need to find the capacitance that creates a lower limit of 20 Hz. {20 = 1/[(2pi)*c*10000]}, or .79 microfarads.

3. This is a little unfair because I heard the answer in class, but you would create another capacitor/resistor combination in series with the original combo. I'm actually not entirely sure why this would create a sharper cutoff, but I would assume the additional capacitance and reactance creates a higher overall voltage loss.

Final Project 

As my project stands right now, it's still digital because of the use of Max/MSP. I've been planning on substituting some sort of oscillator for the laptop though, and I'm going to have to improvise a way to emulate the EQ/Filter functions in the max patch. So, not really sure how to go about drawing a schematic right now because I haven't figured out what components make an EQ or how to have this information changing based on piezo electric signals.