On 6/23/06, Robert A LaBudde wrote: > At 01:22 PM 6/23/2006, you wrote: > >Basics: > >http://www.chm.davidson.edu/ChemistryApplets/spectrophotometry/Spectrophotometry.html > >http://pharmlabs.unc.edu/spectrophotometry/text.htm > >http://www.ruf.rice.edu/~bioslabs/methods/protein/spectrophotometer.html > > I recently made a spectophotometer out of a photodiode, a high-power green > LED and a digital voltmeter. I simply cut a piece of 2x4" wood, bored a > hole for the test tube / cuvette vertically, went crosswise with a hole for > LED and detector, push them in, sealed the holes with black RTV, and was > ready to go. > > Seems to work about as well as my Sequoia-Turner spectrophotometer. You've built a photo colorimeter with one fixed vawe lenght around 550nm which is usefull only for a few applications, (unfortunately the chemists will tell you all applications they need are far away from 550nm...) and not a spectrophotometer. In old days russians were built such colorimeters with up to 12 wavelenghts using some filters and a simple bulb as light source. Heavy but precise. If you really want to see what you've built try to measure transmissions between 3% an 10% and 90% to 100%. If you're able to keep you error below 0.5% than your photocolorimeter is good. greetings, Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist