
In High School Chem Labs, Every Cameraphone Can Be a Spectrometer  - olefoo
http://www.wired.com/gadgetlab/2010/10/in-high-school-chem-labs-every-camera-phone-can-be-a-spectrometer/
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dnautics
crud... I came up with (and executed) that idea four years ago, but it worked
using a series of perl scripts piped together, no way I could deploy that to
high school chem labs. By the time I learned how to program android, there
were other, more capitalizable ideas...

The way it worked was to instead to use a 96-well plate (indexed, by blotting
out certain wells) that would allow the software to key the matrix of wells
and determine 'circles' to sample optical density based on the rgb values of
the resulting jpg image - averaging across the entire circle. The experimenter
would set up a 'calibration curve' in certain pre-indiced wells.

Typically you would have to have a color filter - i.e. if the color being
evolved was yellow then you would take the photograph in blue light.

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jorleif
Would you care to enlighten a bit on the accuracy of the device? I think that
a chemical analyser in everyone's phone would be very useful for example in
detecting toxic substances in consumer products (e.g. cadmium in cheap
jewelry). Would it be able to do that? A second application that comes to mind
is to improve recycling by allowing people to scan the items they are throwing
away.

Could it also do anything related to measuring contaminants in air or water? I
live by the Baltic sea, which is very badly eutrophied, and have for some time
had the idea of a network of floating sensors that would measure with high
detail the nutrient levels. If one could pinpoint sources down to individual
agricultural fields, I think huge reductions in fertilizer runoff would be
possible.

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dnautics
well you had to have a colorimetric assay, which might not be so easy for a
DIY project. We were testing alkaline phosphatase activity, which generates a
yellow color with paranitrophenol, but only when you put a lot of stubstrate
in - actually outside the michaelis-menten range (enzymologist cringe). There
are other things you can test, like phosphate concentration using malachite
green... But the real limitation is what's a reliable visible colorimetric
assay. It's also not something _just anyone_ can reliably do, you have to be
trained in how to use a pipet, etc, which is possible for a dedicated high
school science lab, but might not be for just anyone to do without specific,
supervised training.

One of the other problems was I couldn't figure out how to do nonlinear
fitting in perl... The RGB density:concentration was a polynomial of order
-3/2 (IIRC) Got too lazy with proprietary mathematica fitting to figure out
how to do it myself.

If you're really looking to do real-time floating sensors (which I suspect is
overkill) you wouldn't want to use what I developed... I bet I know people who
might be able to help though, that sounds like a real project with a real
need.

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petercooper
It's amazing what people are coming up with for extra uses for phones.

Tangentially related.. someone on Twitter just convinced me to buy "Instant
Heart Monitor" which turns at least iPhones and Android phones into heart rate
monitors. In my case it used the flash on the iPhone 4 to light up your finger
and works out your heartbeat from fluctuations in its color. My first test
proved accurate.

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asdfgh
Sorry, physics noob here, need more instructions on how to put this together.

Is there a bill of materials and a schematic on how the setup looks from
above?

