06 : Input & Output Devices

This week, taking advantage of the electronic inputs task, I played around a bit with sensing and began to think more about how to make the theremin work with capacitors.

My general idea is that, by coiling two wires together tightly, I can get a capacitor with each wire functioning as a plate. Then by capacitively sensing my hand's proximity, I can map the signal to a pitch on my arduino.

Once Again; How do Theremins Work?

My hope initially was to figure out how theremins sense, because it doesn't seem to just be a normal capacitor. I saw that you can generate oscillations by placing an inductor and a capacitor in parallel, forming an LC circuit:

My first soldering job.

I did so, and I tried to map the oscillation using the oscilloscope. I supplied a brief voltage to the LC circuit at intervals with my arduino, and I tracked the resulting voltage shifts:

My first soldering job.

It was pretty difficult for me to figure out where I could see the signal, but after some fiddling I think I got something similar to what I was looking for. We see that, after the voltage is supplied, a periodic wave follows. Furthermore, if a lower voltage is supplied, this wave decays more rapidly.

Though I was glad I found something that looked like it could be related to something I'd learned about, I still had no idea how to translate that oscillation into meaningful information. Instead, I shifted focus to the coiled wires.

Once Again; How do Theremins Work?

I set up the wire antenna exactly the same as when we made capacitors in class, using the same code to measure a signal:

My first soldering job.

The resulting sound wasn't super clear---for whatever reason, it was really choppy. I also noticed that all of the wires were simultaneously serving as capacitors---bumping the table completely changed the readings.

I also experimented with different lengths of wire:

My first soldering job.

It felt like the short, straight wires actually produced the clearest sound, with the long, tightly-wound wires varying much more wildly. It might be beneficial to not have a high capacitance, as a really high capacitance starts involving a lot of the world around you, instead of just the hand you care about.

Finally, I graphed the signal recieved by the theremin as a function of my distance from the theremin, taking an average to make the signal a little more stable. Luckily, this looked sort of logarithmic with distance, which is what I was expecting!

My first soldering job.

In all, I think I learned a lot! Though the antenna was ultimately subpar, I think I'm slowly getting a feel for how electronics work.