Lab Report 6

Experiment

Our experiment for this week was to build a voltage controlled square wave oscillator using a schematic given to us in class. Most of us didn't have much experience working with schematics, so the main challenge for us was figuring out how the circuit should actually look on our breadboards. I finally figured it out after a very frustrating half-hour, and here is the final result. The variable resistor controls the frequency of the oscillator.

The next step was to add a switch in between the output of the 555 timer and the audio output. This made it so the signal only went to the output when the button was pressed.

We also made circuits where the button bypassed the signal to ground. This made it so the signal was cut when the button was pressed. I forgot to take a picture of this, but it was basically the same circuit as above, just with a wire running from the button to ground.

Lastly, we added another potentiometer, but this time it was affecting the pan of the signal. The signal was routed into the middle connection on the potentiometer, and the left and right outputs were routed to their corresponding sides. This created a pretty solid panning effect.

Questions

1. For me at least, the most difficult aspect of working with the schematic was keep track of the wire paths. There were a few connections that were also connected to power, but since the power source symbol was in the corner of the diagram, it was easy to miss. It's just a matter of visualizing what the connections actually have to look like, since we are basically told what the wires need to be connecting, but not how to concretely achieve those connections.

2. You would use a peak follower, which we made in the last lab, then output that voltage to the 4th input on the timer (I think), and you would get rid of the variable resistor and use a set resistance. I'm not entirely sure, but you would have to use the output voltage of a peak follower to change the oscillator frequency, and it seems like the 4th and 5th inputs on the timer dictate the frequency.

3. I think you would have the incoming signals wired to the left and right terminals of the potentiometer, then have the center terminal connected to the audio output. This would be affecting the resistance for each audio input.

Final Project

1. Drum controller. Uses multiple piezo disks and pressure sensors to detect pressure and location of finger on control surface and then outputs voltage to an oscillator and filter.

2. Piezo and pressure sensors, speaker, voltage controlled oscillator (maybe 2 or 3 depending on how many control surfaces I want to have), voltage controlled filter (possible multiple), control surface (I was thinking a wooden bowl).

3. I will probably have to buy materials to make multiple oscillators and filters, the control surface (which I haven't fully figured out yet), and some sort of speaker set-up.

Lab Report 5

Experiment

Basically, the purpose of this experiment was to show how diodes affect AC signals. This was achieved by placing a diode within our audio circuit in a few different arrangements, and using oscilloscopes to visualize the signals. 

Here is the first circuit we made, which was simply running our audio signal through the diode, and the diode was input with it's bias facing the output jack. The oscilloscope was connected both before and after the signal went through the diode.

Here's a picture of the oscilloscope results. The diode basically truncated the negative portion of the signal, and reduced the peak voltage a little bit. This was the test at 200 Hz, and at 1000 Hz and 10 kHz, the slope of the truncation was different. At 1000 Hz, the diode signal didn't follow the shape of the unaffected signal, and at 10 kHz, the voltage level the signal was cut off at seemed to be higher.

200 Hz

10 kHz

The next circuit we used was essentially the same circuit, but the diode's bias was reversed. The effects were very similar to the forward biased diode, the main difference being that the positive portion of the signal was truncated, instead of the negative side.

200 Hz

10 kHz

The next circuit we built connected the diode to ground, instead of having it run directly to the audio output. Here is a picture of this circuit. A resistor was also added to the circuit. 

The oscilloscope showed that the signal was cutoff at a certain positive voltage, and the voltage it cut off at depended on the volume of the signal. There also seemed to be a threshold volume where the signal began to be cutoff, and any volume below this threshold showed no change in signal. The effect was basically the same at all frequencies I tested at. When I reversed the bias of the diode, it had the same effect, but the signal was cutoff at a negative voltage. Unfortunately, I forgot to take a picture of the reverse biased diode, but I think you can get a pretty accurate idea of what it looked like from the forward biased diode. 

Forward Biased Diode to Ground

The last circuit we constructed was called a peak follower, which is a forward biased diode connected to a capacitor. The capacitor is then bypassed to ground.

The peak follower did its job and output a signal that was relatively flat at the peak voltage of the input signal. As frequency increased, the peak follower line became straighter and more uniform. Also, when I took out the capacitance, the base line of the output voltage went back to 0, and was basically the same output as the forward biased diode circuit from earlier in the lab. I also tried a few different values of capacitance, and found that higher values of capacitance will make a straighter output line.

Capacitance: .1 microFarad

Capacitance: 1 microFarad

Questions

1. The peak follower could essentially act like a vocoder, because it will output the peak voltage of an input signal. The output signal could then be used to control the frequency, cutoff frequency, or amplitude of a VCO or VCF etc. There are a ton of musical applications for this sort of set up.

2. To isolate the bassiest frequencies of an input signal, you would need to run it through lowpass filter first, then connect the filter to the peak follower circuit. 

The values of the capacitors would probably be changed, and a variable resistor would work better because you would be able to pinpoint the corner frequency that isolates the bass drum.

Final Project

To be completely honest, I haven't been giving my final project a whole lot of thought recently. However, I'm fairly committed to this ResoDrum idea. I think a peak follower would be very useful actually, because I need to somehow convert the pressure on the bowl into some sort of control voltage. If I can use piezo disks to convert the amount of pressure on the bowl, I think this will be not too difficult to pull of. I'm mostly worried about figuring out the oscillator/filter set up I would need to make the drums actually interesting to use.

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.