# Communication System Based on Magnetic Coils for Underwater Vehicles
## 4 Experimental Tests  
To verify the proposed communication system, the printed circuit boards of the transmitter and receiver circuit described in the previous section were built as shown in Figure 10.  
To evaluate the underwater communication system, a submersible transmitter module was built, which uses a 14.8 V battery, a regulator, n embedded Raspberry Pi computer, a USB\(\leftrightarrow\)serial converter, a transmitter circuit, and a transmitter coil.  
The receiver system was placed in the prototype of an underwater vehicle based on the BUIEROV2 robot, which has been used in different applications such as evaluation of control laws [28] and marine research [29]. The mechanical structure of the vehicle is made of polyethylene and acrylic tubes where the electronic components are located.  
Figure 9: Comparison of emitted and received signals.  
The underwater vehicle has an embedded Raspberry pi computer to implement the algorithms for control, navigation and signal processing. The system works using the Ubuntu operating system under the Robot Operating System (ROS) programming environment, an open-source code environment developed especially for robots. Under this architecture, programs were designed to access data from the pressure sensor, inertial center, transmission of control signals for the thrusters, teleoperation signals, etc.  
Regarding the interface with the proposed communication system, a Python program was developed that connects to the universal asynchronous receiver-transmitter (UART) serial port of the USB\(\leftrightarrow\)serial converter. In this way, it is possible to access the data read by the receiver magnetic coil.  
A program was also designed that stores the received data in a text file, which allows for its subsequent analysis.  
The receiver coil was mounted on the front of the mechanical structure of the underwater robot, the receiver circuit was placed inside the capsule in which the robot's computer is located and the connection is made using a hermetic connector, the coil is connected to a separate battery that is used by the underwater vehicle's control system.  
Figure 11 shows the description of the experimental tests which are defined as follows:  
1. Start the transmitter system, which must be programmed to periodically send a message containing a password and a string of test characters.
2. Submerge the emitter module to a depth of at least 1.5 m.
3. Activate the underwater robot and launch the teleoperation and data reading programs. The latter must be connected to the port where the receiver system is located.
4. Submerge, through teleoperation, the underwater vehicle in such a way that the coils are at a distance of approximately 20 cm, horizontally.
5. Activate an information storage program which should save the string of test characters received from the transmitter module in a file for further analysis.  
The use of a password is recommended during the transmission tests to avoid storing erroneous data produced by noise. It is recommended to submerge the emitter module at least 1.5 m to ensure that the magnetic field lines generated propagate only in water. Finally, it is also recommended to place the receiver coil at a maximum distance of 20 cm from the transmitter coil to ensure that it is placed within the coverage area of the transmitter system (this distance may change depending on the characteristics of the magnetic coils used for transmission).  
Figure 10: Construction of the transmitter and receiver circuits.