DIY Spectro II

Posted: March 15th, 2011 | Author: csoeder | Filed under: DIY Spectrophotometry | 3 Comments »

There is a companion article focussing on the technical details of this project over at TopologicOceans

At long last, second generation DIY spectro has arrived!

The spectrophotometer. Yes, that is an invisibility cloak. You can't see the stuff that's under it can you? Then that stuff is invisible!

If you recall, when last we left our humble spectrophotometer, it was a shambling mess of stone-age technology. Now, its a shambling mess of information-age technology!

The principle is the same: A light source is split into its component frequencies, which are passed through a sample, and a detector measures its intensity. The intensity at each frequency is compared between a blank sample and an analyte to calculate the absorption spectrum.

Much of the heavy lifting (motor control and sensor reading) is now done by an Arduino microcontroller with Python on the other end of the USB cable:

The great commuicator.

The microcontroller controls the motor assembly and sends sensor data to the computer for analysis. The guts of the machine look a bit different, too:

The moving parts of the machine. You can see the motor peeking out from below the flashlight, and the sensor in the background.

And best of all, it appears to work!

A subplot in William Gibson’s book Count Zero involves a collection of abstract art pieces, consisting of seemingly random scraps of material assembled into unsettling but delicately beautiful arrangements. Though it didn’t occur to me during development, the aesthetic stuck. But did I take the route I did simply because I enjoy gluing pieces of trash to other pieces of trash? (and oh how I enjoy it!) One commentor remarked:

‘the project seems like a spoof on all the meticulously documented, high-production-value projects out there. I mean, masking tape, not gaffer’s tape? A TP tube, not a hunk of PVC?’

I could have sat down and planned the whole device from start to finish, designing blueprints in AutoCAD and precisely manufacturing the parts out of high-quality materials. But I didn’t do that- because I planned from the beginning to fail.

When I was a kid, I tried to build a drum machine using sticks and rope and powered by a rock which would fall from my treehouse. I planned it out with pencil and paper, every part in its right place, the connections between parts simple and obvious. And I put it together.

And it didn’t work. Some considerations were minor, but together they built up; other considerations weren’t obvious until the whole thing had already failed. Reality refuses to follow our plans for it.

Instead of starting with a schematic derived from theory, my process was of building and then unbuilding scaffolding, combining already functional modules and tweaking their arrangement until their assembly was a new module. I encountered unforseen difficulties sequentially, and in the context of a previously functional machine, rather than all at once, without context. In a sense, I helped the machine evolve by adding just the right bit of aluminum here or rerouting a wire there, contingency by contingency. As engineer Henry Petroski once wrote, technologies ‘do not spring fully formed from the mind of some maker but, rather, become shaped and reshaped through the (principally negative) experience of their users’.

Though the ultimate goal is to have a standardized open source instrument without the evolutionary contingencies and analog fiddling, I suspect that DIY Spectro hasn’t seen the last of the functional kludges. Part of the appeal of open source instrumentation is that it democratizes science. Besides hobby and educational applications, low cost instruments have potential for third world communities. There are all kinds of environmentally and medically relevant colorimetric tests (eg, for oxygen demand, nitrate concentration, pH, glucose…) which low cost spectrophotometry could support. However, these communities may well lack access to the specific parts of a given hardware project, due to lack of funds for manufacture and transport, and inconsistent supply lines. And as time progresses the environmental, social, and economic costs of a manufacturing and transportation system dependant upon fossil fuels may well rise making current resources less sustainable and possibly inaccessible. However, all the while we have been digging up the world’s mineral wealth, we have been reburying parts of it, stored in the material and organization of discarded technology. The gear system in this model was pulled out of an old floppy drive- how many floppy drives are wasting away in dumpsters across the world? Already, the first world exports its technologic waste to the third world, where it is destroyed for its precious, though toxic, mineral wealth. It’s a sick example of structural ecological inequality. But careful reuse of prebuilt technology might actually sequester those toxins- if you don’t break open a module containing lead, you don’t put that lead into the environment. This approach could help developing and alternative communities.

Also its really fun to glue pieces of trash together.