# FUXYA2020: A Low-Cost Homemade Portable EDXRF Spectrometer for Cultural Heritage Applications
## 2 FUXYA2020 Design and Characteristics
### Assembling  
Once the geometric configuration of the tube-detector was established, the final integration between these two components was designed using a 3D design software (Figure 3). The enclosure includes a base with four support feet at the bottom, and three holes to secure a Manfrotto 200 PL rapid plate so that it can be attached to a tripod. In addition, the X-ray source and the detector unit have been positioned so that the intersection point between the X-ray beam from the X-ray tube and the detector axis, i.e., the \"focus\" of the instrument, is about 10 mm away from the base of the instrument; the distance between the X-ray tube and the sample is thus about 14 mm, while that between the sample and the detector is about 34 mm. The current distance between the instrument and the sample can be reduced simply by shifting the components on their axis; nevertheless, choosing a 45\({}^{\circ}\)-45\({}^{\circ}\) geometry, the size of the detector head must be considered. If a significantly lower distance is preferred, the geometry should be changed, either by reducing the scattering angle and keeping the irradiation angle equal to the detection angle, or by maintaining a 90\({}^{\circ}\) scattering angle with a different geometry (such as a 60\({}^{\circ}\)-30\({}^{\circ}\) geometry).  
Thanks to the 3D design software [46], the measurement spot is easily calculated on a flat sample: when using the 1 mm collimator for the X-ray tube, the area irradiated on the sample is about 8 mm\({}^{2}\) and has an obviously elliptical shape (Figure 4). To complete the FUXA2020 system, a cover was created, which includes a co  
Figure 3: Positioning of the components for FUXYA2020 spectrometer. Dimensions are given in mm.  
Figure 2: Geometrical configuration of FUXYA2020 spectrometer.  
two USB fans (5 V), one positioned at the top, in correspondence with the detector, and the other laterally, close to the X-ray tube (Figure 5).  
Furthermore, inside the case we placed a positioning system run through an Arduino UNO board and composed of the following electronic components (Figure 3): a laser sensor module (KY-008) with a spot size of 5 mm (outer diameter of 6 mm) to verify the investigated area, and a VL6180X time of flight (ToF) distance sensor to position the sample in correspondence with the focus of the instrument, maximizing the spectra intensity and allowing repeatable and comparable measurements. The VL6180X is an optical module that includes a proximity sensor, an ambient light sensor, and a VCSEL (vertical cavity surface emitting laser) light source which emits in the near-IR at a wavelength of 850 nm. The distance sensor has a spatial resolution of 1 mm and an accuracy of about 1% at 50 mm distance. We did not choose an ultrasonic sensor as it is not suitable for non-flat surfaces; moreover, differently from an IR sensor (whose range of distance is also out of the scope of the present project), ToF measure should be independent from the sample reflectance. We also integrated an I2C 1602 LCD display to show the distance measured by the sensor, a button to easily turn on and off the laser module and two LED diodes that light up according to the distance from the sample. All these components can be bought at a low price, according to the financial availability of the research group.  
To make a low-cost instrument, all the structural components of the FUXYA system were 3D printed in PLA (polylactic acid) except for the base, which was cut out from a PVC sheet for greater structural strength (Figure 6). The maximum footprint of the FUXYA system is 295 \(\times\) 210 \(\times\) 76 mm, similar to the size of an A4 sheet of paper.  
Figure 4: Sample irradiated area when using the 1 mm collimator for the X-ray tube (a \(\cong\) 1.91 mm, b \(\cong\) 1.35 mm).  
Figure 5: FUXYA2020 external case. Dimensions are given in mm.