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There are many applications that require compact spectrometers that yield results quickly. For example, farmers need to check the soil quality regularly by monitoring its nutrients (Nitrogen, Phosphorus, and Potassium, etc) . Also, it is necessary to test the quality of products like fruits, vegetables, and meat. Conventional laboratory analysis techniques are tedious and time-consuming. Near-infrared reflectance spectroscopy can analyze solid and powder samples without sample preparation by fingerprint molecular absorption. Diffuse Reflection (DR) contains information about the internal and external characteristics of the sample. Commercial NIR Spectrometers are expensive due to the use of linear array detectors that work in the IR region. The lack of domestic suppliers for such components also increases prices. In this work, we look at designing an inexpensive and compact optical system that can be used for diffuse reflectance near-infrared spectroscopy. The samples will be in powder form, requiring simple preparation, enabling ease of use. A Digital Micromirror Device (DMD) along with a single photodetector will be used in the spectrometer rather than a linear array detector. DMDs consist of an array of micromirrors. With suitable optics, they can be used to divert the diffracted spectrum to a single InGaAs photodiode. The NIR spectrometer design is based on the commercial detector active area with a 2 mm diameter and DMD dimensions of 5 mm in length. We describe how to choose the specifications of the grating and other optics in accordance with the detector's active area and DMD dimensions. The NIR spectrometer was designed to work in the spectral range of 1100 nm to 2400 nm with a spectral resolution of 2 nm.
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