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Building Affordable Photodiode Spectrometer

Submitted By: 

Shalini Verma

With a goal to develop an inexpensive spectrometer, bhickman on his website has designed and explained the process of making an affordable spectrometer. The resolution of the same is comparable to lower end commercially available spectrometers. Further, approximately 0.6 nm wavelength resolution is being provided by the current design and around 12-bit intensity resolution.

Generally, spectrometer should operate in the 400-900 nm wavelength range but to get the exact wavelengths, some changes are needed because of the discrepancies between the theoretical and actual design. Hence, a halogen bulb has been used as the light source and the design is accordingly modified to handle the heat generated. Further, some thoughts are required to find the way to eliminate higher order light interference.

Building affordable photodiode spectrometer

As far as design is concerned, the spectrometer is developed using a Texas Instruments called StellarisLaunchPad microcontroller. It is programmed with Energia which is identical to the Arduino IDE. The device also includes a photodiode array, a light source, LED holder, a collimating lens, a diffraction grating, two project boxes, a wooden cuvette holder, and a wooden base as the optical platform.

A spectrometer becomes quite expensive when it is used to read the UV range of light while the target wavelength ranges between 400 nm to 900 nm. Therefore a better option is needed to accommodate this particular geometry to achieve this desired wavelength range and hence the diffraction grating equation is used.

According to the equation, the intensity of light decreases with distance and hence the distance of each photodiode must be close to the diffraction grating as much as possible. In such case, the geometry gets further restricted in the system and one edge of the photodiode becomes 23.58°, which is the grating’s normal distance from the grating.

The complete information is available at the following link along with the mathematical equation and video for assistance.