a low cost led based spectrometer
a low cost led based spectrometer is described. this led based spectrometer could be operated as a standalone instrument or under pc control via serial link. a total of seven wavelength selections are available by the plug-and-measure led light module. with the seven wavelength selections, the led based spectrometer could provide qualitative visible absorption spectra that predict the absorption maximum. based upon the qualitative visible spectra, quantitative photometric information could be obtained.
there is a need in many resource limited countries and laboratories for a low cost analytical instrument that could provide both qualitative and quantitative chemical information. there are also great needs for low cost autonomous instruments that could help monitor the fragile environment around the world on a global scale.1,2with the advances in modern electronics, microcontrollers could provide great capabilities to acquire and process sensor signals. the development of compound semiconductor manufacturing technology could also produce many leds with wavelengths from ir down to the 365 nm uv range. with its compact size, a wide range of selections of available wavelengths and low power consumption, leds are used extensively in analytical instruments as light sources.3-15 dasgupta et. al. gave a very detailed review for led application in flow injection analyses.3,4 led light sources for sensor applications were also extensively reviewed by kostov et al.5-7 hauser et al.8-10 built a multi-wavelength spectrometer to analyze aluminum, copper, ammonia, calcium, phosphate, chromium, and nitrile. in his work, leds with seven wavelengths and a 2*7 fiber optic coupler were used to construct a multi-wavelength spectrometer. the 2 *7 fiber optic coupler would greatly increase the cost of the spectrometer and would not be suitable for large scale employment. hamilton et al.11 built a four color led photometer with a material cost of about us$ 200. the led photometer was designed with analog circuits and thus was not very flexible or user configurable. knagge et al.12 built a spectrometer with a mini light bulb, diffraction grating and lego block. the material cost was also about us$ 200. this spectrometer was not robust or inexpensive enough for large scale deployment in the field. cantrell et al.13 designed a slim spectrometer with red, yellow, and blue leds. the total cost to construct the slim spectrometer is about us$ 25. a tsl230 programmable light-to-frequency converter from texas advanced optoelectronic solutions (taos) was used as photo-detector for the slim spectrometer. the slim spectrometer is low cost, low power consumption and robust, thus it is very suitable for autonomous instruments employed in the field. the only limitation is the available wavelength in the slim spectrometer.
