Guitar pedal based science project ideas?

[ParkAvenger]

So, I'm required to find or come up with an idea for a science project for my Chemistry class (although I'm not limited to chemistry-based experiments). I'd like to do something I'm actually interested in for the project, and when thinking about what that might be, I thought of my desire to get into DIY pedal stuff - which time has not allowed me to really do yet (rewiring my guitar being the exception). So what better way to build something than under the pretext of a science project? 

Of course, I can only do this if I can actually find a good idea. So I was wondering if any of you more experienced pedal-builders could give me some ideas. They don't need to be particularly complicated, but should probably involve something that can be measured in some not-entirely-abstract way (because who doesn't love graphs?  ) Hell, anything that modifies sound in an interesting and preferably measurable way is good, whether or not it would be ultimately practical for playing guitar.

I'm not sure if anything usable will come of this or not (here's hoping!), but it's worth trying, and I'd be interested to hear what sort of stuff you guys can come up with. Thanks 

[km-r]

a theremin? 

[Arfman]

I'd start out going to geo and looking over the "Technology of the " papers...A FuzzFace is a great starter pedal and there is a good article over there that disects how it works...

[sshrugg]

A FuzzFace is a great starter

+1.  That was my first build.

[col]

Someone posted a link here a while ago to their dissertation on the effects of different diodes on distortion sounds. I have the details on my work computer but not here at home. It was downloadable as a PDF and if the link's still live it might be worthwhile doing a search and seeing how he did it for an example. If not I have a copy of the file on CD somewhere. I'd much rather you got it direct off him just in case he doesn't want it in the public domain anymore.

Col

[Mark Hammer]

Although the instructor has widened the aperture for you, I still it would be useful for you to squeeze as much learning about Chemistry as you can out of the project.

So, here's a suggestion.  LED spectral content and photocells.  Nobody here seems to have ever done a parametric study of LED colour, luminance, and photocell behaviour.  Take any 2 or 3 typical photocells in the resistance range of what would be useful for stompboxes, and examine what changing the colour of the LED and brightness does for fall/rise times in resistance.  Extract some general rules from what you observe, and I imagine that would be of inestimable help to the folks here when it comes to DIY optoisolators.

So, given that yellow and orange isn't all THAT far away from red, cany ou produce the same response curve from a photocell with an orange LED that you would with a red, just by tweaking brightness?

[sshrugg]

Although the instructor has widened the aperture for you, I still it would be useful for you to squeeze as much learning about Chemistry as you can out of the project.

Agreed.

So, here's a suggestion.  LED spectral content and photocells.  Nobody here seems to have ever done a parametric study of LED colour, luminance, and photocell behaviour.  Take any 2 or 3 typical photocells in the resistance range of what would be useful for stompboxes, and examine what changing the colour of the LED and brightness does for fall/rise times in resistance.  Extract some general rules from what you observe, and I imagine that would be of inestimable help to the folks here when it comes to DIY optoisolators.

So, given that yellow and orange isn't all THAT far away from red, cany ou produce the same response curve from a photocell with an orange LED that you would with a red, just by tweaking brightness?

Better than anything I would have come up with!

[ParkAvenger]

That is an excellent idea. This project will actually culminate not in a science-fair sort of exhibition, but rather in a research paper, so that idea works out quite nicely - how the photocell responds differently for different brightnesses of different colors.

However, how would I go about measuring the response curve? I have to have quantizable, graphable data for this thing.

[m-theory]

If you wish to use a pedal project as a basis for your chemistry project, you'd probably be best off discussing the various component compositions, why a particular element is chosen for a given transistor, why copper is chosen for conductive bridging, what happens to copper when exposed to oxygen, why silver is sometimes used, etc.  There are lots of very deep, worthy discussions of the specific materials used in the building of pedals that live squarely in the world of chemistry.  The battery that powers the device works because of a chemical reaction as well.  Some folks etch their finished products with acid.  That's obviously a chemical reaction.

There are no doubt many worthy discussions involving the science of physics, with regard to pedals, including the above-mentioned electromagnetic frequency analysis, but if you wish to aim your project towards chemistry, I believe you're going to want to examine the core elements used in the construction of the devices, not the physics behind them.

[Solidhex]

Oddly enough my first build was a theremin. Etherwave kit.

--Brad

[MarcoMike]

what about making components from chemicals? Transistor may represent a problem though... mh
and / or you can make a coloured VUmeter which changes color with electrochemical reactions.... it may be not so fast, but quite challenging in my opinion!

by the way...I'm a chemist, if you need suggestion feel fee to ask

[deathbringer07]

light is in the field of physics...

[Mark Hammer]

And photochemistry is in the field of chemistry...happily...and by definition.

Measurement would require a means of measuring resistance, or indices of it, over short periods.  That invariably turns to a scope, whether hardware or software-based.

At least part of what you'd be measuring, as I see it, is the photochemical change in response to brief periods of illumination.  That is sort of the fundamental aspect of LDRs that makes our lives so perplexing here.  LEDs can illuminate for ridiculously brief periods, but the photochemical changes they induce in an LDR take longer to occur and generally even longer to reverse.  Essentially, what you're dealing with is a transient punctate event causing a graded sllow event.  The mystery for us here is understanding what sorts of time-related changes occur and what makes them occur faster and slower.  Generally, when you're dealing with things like envelope followers (which photocells are often harnessed to), the operating curves of the circuit can be tweaked in predictable ways.  The trouble is, it is hard to tweak them in advance based on a priori knowledge of the photocell, especially if the photocell is a DIY unit.  You end up having to season the driving circuit to taste based on in in situ operating characteristics of the photocell.  It would be far better if one could know what the photocell is going to do before you build the circuit. 

Case in point.  We drive ourselves bonkers about wah pot taper.  Why?  Because the rate at which one moves through different zones in the centre-frequency of the filtering that a wah provides determines its expressiveness.  Spend too little time (as a function of the proportion of time allocated in a typical back-to-front-to-back foot-movement of the treadle) in one frequency range, and too much time in another, and the wah just doesn't cut it.  Part of that is marrying up the taper of the pot with that rage of foot/ankle movement over which we have the greatest control and articulation, but since we can't really change the design of the human foot it still depends fundamentally on being able to peg down a desirable pot taper that extracts the very best control from the human foot, in service of pleasing sounds.

When it comes to things like envelope-controlled effects, whether wahs, gates, compression/limiting, or other side-chain controlled devices, the photocell takes on the role of foot.  It is that thing with certain operating characteristics we can't change, but which is merged with a circuit that we CAN change.  So, the trick in knowing how to tailor the circuit is to know how the photocell behaves, and the trick to knowing how the photocell behaves is to have parametric data about what percentage of resistance is restored (or reduced) within what period of time, at what illumination.  The illumination can be supplied by LEDs of comparable brightness (in mcd ratings) with various known current-limiting resistors in series.

If that wasn't complex enough, there are "memory effects" to consider.  To cite the PerkinElmer Guide to Optoisolators ( http://optoelectronics.perkinelmer.com/content/RelatedLinks/Brochures/BRO_PhotoconductiveCellsAndAnalogOptoiso.pdf ):
"The speed of response depends on a number of factors including light
level, light history, and ambient temperature. All material types show
faster speed at higher light levels and slower speed at lower light
levels. Storage in the dark will cause slower response than if the cells
are kept in the light. The longer the photocells are kept in the dark the
more pronounced this effect will be. In addition, photocells tend to
respond slower in colder temperatures.
Light History
All photoconductive cells exhibit a phenomenon known as hysteresis,
light memory, or light history effect. Simply stated, a photocell tends to
remember its most recent storage condition (light or dark) and its
instantaneous conductance is a function of its previous condition. The
magnitude of the light history effect depends upon the new light level,
and upon the time spent at each of these light levels. this effect is
reversible.
To understand the light history effect, it is often convenient to make an
analogy between the response of a photocell and that of a human eye.
Like the cell, the human eye's sensitivity to light depends on what level
of light it was recently exposed to. Most people have had the
experience of coming in from the outdoors on a bright summer's day
and being temporarily unable to see under normal room levels of
illumination. your eyes will adjust but a certain amount of time must
elapse first. how quickly one's eyes adjust depends on how bright it
was outside and how long you remained outdoors.
The following guide shows the general relationship between light
history and light resistance at various light levels. The values shown
were determined by dividing the resistance of a given cell, following
infinite light history (RLH), by the resistance of the same cell following
"infinite" dark history (RDH). For practical purposes, 24 hours in the
dark will achieve RDH or 24 hours at approximately 30 fc will achieve
RLH."

So, does that sound interesting?  I know it's useful, but it'll be useless as tits on a bull if you don't find it interesting enough to follow through.

[theonlyrobkeyser]

It seems to me like any given pedal could be a science project.  Most people I know don't even know the exist, so showing them one and explaining the inner circuitry could be a pretty good project.  If you have to perform an experiment there are lots of options too.  Many of the fuzz circuits have transistors with gain curves that are linear for a while, then flatten out (where they start to distort and sound cool).  You could get the graphs from the data sheets, or measure them for your self and then investigate different biasing points.  But the cool part is explaining how the physical phenomena creates a sound we like. 

[geertjacobs]

The first thing I thought of when I read "Chemistry" was etching enclosures.

[Mark Hammer]

There's projects and there's projects.  My sense is that the assignment is to do something more on the order of a study, rather than a science-fair "the Solar System" kind of description (which is essentially what explaining the workings of a pedal would be).  If I've understood it right, the goal is to demonstrate use of concepts in chemistry in an applied context by using them to measure something.  In this case, assuming that what I suggested is still of interest to PA, it is the speed of the chemical reaction as a function of the photo-catalyst properties.  The practical byproduct of that for our purposes is predicting what sort of resistance changes to expect, but the underlying chemical aspect is the photo-chemical reaction itself.

[deathbringer07]

^yeah how bout pcb etching.. but instead of a circuit, why not etch ur name?