## 2 Materials and Methods
### External Ports  
With regards to the Ethernet port, the WE-MJ Femi Shielded 8P8C Ethernet connector [45] was chosen for this design. The eight signals associated with this connector are routed to the JB\({}_{1}\) high-speed connector [46], enabling them to be managed by the Marwell Alaska 88E1512 Ethernet transceiver [47], which is integrated into the TE0720 board [22; 42].  
For the USB type-A port, the four signals from the universal serial bus (USB) Type-A port are routed to the pins of the high-speed connector JB\({}_{3}\)[48], where they interface with  
Figure 21: Internal interface PCB: (**a**) top view; (**b**) bottom view.  
the USB3320 integrated circuit (IC) [49]. This IC is housed on the TE0720 board [22; 42], facilitating USB communication and functionality.  
As for the JTAG, the DIGILENT 410-299 JTAG-HS3 Xilinx Tool programmer cable [50] is utilized for programming the joint test action group (JTAG) of Xilinx FPGAs. To facilitate this, a JTAG port compatible with the DIGILENT JTAG-HS3 was integrated into the external interface board, providing a connection point for the programmer cable.  
For the UART, the TTL-232 RG cable [51] was used to handle the universal asynchronous receiver/transmitter (UART), serving as a TTL-to-USB serial converter. To facilitate this connection, a three-pin header port [52] was integrated into the carrier board. This header offers a connection for the TTL-232 RG cable, enabling communication with the FPGA through a serial port.  
With regards to the microSD socket card, the implementation of a socket for reading micro secure digital (SD) cards is vital because the system's programmable hardware, managed by the FPGA, is stored on a microSD card. Additionally, the software that runs the system application is also stored on this microSD card. If the microSD card is not inserted, the FPGA must be programmed using the JTAG programming cable.  
Concerning the high-speed connectors, the board is equipped with three Razor Beam High-Speed Hermaphroffic Terminal/Socket Strip connectors: one 60-pin connector, labelled JB\({}_{3}\), and two 100-pin connectors, labelled JB\({}_{1}\) and JB\({}_{2}\). These connectors are located on the top side of the printed circuit board (PCB). In this manner, the signals from the Ethernet, USB Type-A, UART Tx and Rx, and JTAG ports are connected to the TE0720 board via the high-speed connectors JB\({}_{1}\), JB\({}_{2}\), and JB\({}_{3}\).  
On the other hand, the LiFi router external interface board requires a 12 V voltage supply. This voltage can be provided in two ways: (i) via an AC/DC adapter equipped with a jack power connector, or (ii) through a 12 V battery. The battery cables are connected to the external interface board using a clamp. The input voltage of the power module connects to the isolated DC/DC converter PDQE20-Q24-S12-D [53], which supports input voltages ranging from 9 V to 36 V and outputs 12 V with a current capacity of up to 1.66 A.  
Similarly, the USB dongle external interface board is powered by a 5 V supply. This voltage can be provided in two ways: (i) via an AC/DC adapter with a jack power connector, or (ii) through a USB Type-C cable connected to the user's laptop or other device.  
Figure 22 depicts the actual physical appearance of the LiFi router external interface PCB and the USB dongle external interface PCB following the manufacturing and soldering process. The LiFi router external interface PCB measures 8.6 \(\times\) 9 cm\({}^{2}\), while the USB dongle external interface PCB measures 6.85 \(\times\) 9 cm\({}^{2}\).