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When we looked for a spectrometer for our localized plasmon resonance sensing device, we either had the choice of using an expensive commercial 5000$ spectrometer or building one on on our own. We found many diy photometers but not alot of diy spectrometers. Photometers are far easier to built then a spectrometer, since only one specific wavelength is measured. This specificity though, does make them not as versatiale as spectrometers. For alot of applications like LSPR only spectrometers are applicable. So we decided to built one on our own. We designed our spectrometer in a way that it can be used for other applications, not just LSPR sensing.

At first, we reviewed already available spectrometers. We started with looking into publications on cheap spectrometers^[1]. The biggest problem with these is that they do not give actual construction data and are only result orientated. So we concentrated on open source diy designs. The ramanPi spectrometer caught our eye^[2] and we based our design on it. The greatest upside is, that it was developed open source with a detailed construction documentation.
On the other hand, the ramanPi spectrometer project was never finished and validated. Also the design lacks adjustability for the optics that need focussing. This is the most important part of a spectrometer, because every small deviation of the optical components from their optimal position results in a drastic reduction in the spectral resolution.
To solve this problems, we changed and optimized the original design in the following ways:
- changed the position of the diffraction grating to put focus on the 600 nm wavelength
- added adjustable mounts for the slit and CCD Array for focussing
- changed the setup from a commercial 100$ slit to a 5$ razor blade magnet slit
- added holder to mount other probes like cuvettes

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The spectrometer is based on the Czerny-Turner configuration (see figure 2). It features a slit, a collimating mirror, a diffraction grating, a focusing mirror and a charge-coupled device (CCD) sensor. The CCD sensor sits on top of a small printed circuit board (PCB), that reduces noise levels and is connected to a Nucleo microcontroller. The Nucleo can then either be connected to a computer or a Rasberry Pi with a small touchscreen for a graphical output. The firmware and the graphical user interface is developed in the open source project TCD1304 by Esben Rossel^[3].
The Czerny-Turner setup is also used in commercial products, like the Ocean Optics HR4000. These devices start at around 4000$^[4] and house basically the same components as this diy version^[5]. Companies offer their devices at such a high price, because they have mastered the alignment of these optics. The material cost of these is only a fraction of the price.