# Non-Invasive Glucose Measurement Technique Based on Time-of-Flight
## 3 Experimental Setup  
The experimental setup comprises a custom-designed sensor, a sample holder, and a 3D printed adapter. The sensor is built around the Texas Instruments OPT8320 IC (Dallas, TX, USA), which utilizes a phase-based ToF approach to measure distance. This IC drives an external infrared LED (Wurth Elektronik (Waldenburg, Germany), Model 15411085A4570) emitting at 850 nm. This wavelength was chosen due to the sensor's peak transmissivity at 850 nm (see also [13]) and its position within the optical window of tissue, allowing for optimal light penetration (see also Figure 1 in [14]). Additionally, glucose concentration significantly affects scattering at this wavelength range [8].  
The OPT8320 features an 80 \(\times\) 60 pixel sensing array accessible by its sensing engine, enabling individual measurement of each element. By exploiting the sensor's high sensitivity and configurability, it is possible to indirectly measure the degree of light scattering by a sample placed on the sensing element. The experimental setup developed is shown in Figure 2(a).  
Sensor data are output in a custom binary format over a 24 MHz parallel bus, matching the IC's clock frequency. To capture this data, an interconnect circuit based on the Cypress FX3 USB 3.0 platform (Infineon Technologies, Neubiberg, Germany) was developed, which supports direct acquisition of up to 32 bits of parallel data at high clock rates and streams it to a host computer via USB 3.0. The FX3 platform also configures the OPT8320 over an I\({}^{2}\)C interface. This circuit connects the OPT8320 to the FX3 and supplies all of the necessary power rails, derived from the USB power supply. Adequate power supply filtering was  
Figure 3: The experimental setup developed.  
Figure 2: Representation of scattering of light from glucose molecules. Changing concentration affects sample scattering.  
added to mitigate noise from the USB port, following guidelines from relevant application notes (FTDI and Micrel/Microchip [15; 16]). The required voltages are generated using low-noise linear voltage regulators, and the negative bias voltage for the sensor is produced using a switched-capacitor inverter followed by a low-noise regulator. The OTP8320 schematic can be seen in Figure 4. The schematic of the various power supplies used are not included for brevity.  
Software was developed to allow the FX-USB3 to initialize and control both the OPT8320 sensor. Custom software was also created to facilitate data capture from the FX-USB3 to a file on the PC. An example of the data provided, visualized as a grayscale image, is provided in Figure 5. A high-level diagram of the circuit created is shown in Figure 6 and the PCB manufactured and mounted on the FX-USB3 platform is shown in Figure 3b.  
Figure 4: OTP8320 schematic.  
Figure 5: Phase data from sensor, rendered as a grayscale image.  
The sample was contained within a cylindrical cuvette, carefully chosen for its high transparency in the targeted wavelength range (Hellma Analytics 692-091-12, Mullheim, Germany). To ensure it did not influence the measurements, the cuvette's transparency was further validated by conducting tests on both an empty cell and one filled with saline.