# Remote Water Quality Monitoring System for Use in Fairway Applications
## 2 Materials and Methods
### Remote Water Quality Monitoring System Architecture
It has a lifespan of up to 3000 cycles at full discharge (DoD 100%), or up to 5500 cycles at lower discharge (DoD 60%);
* The efficient nanophosphate cells allow for the use of high charging and discharging currents, and the operating temperature ranges from \(-10\)\({}^{\circ}\)C to 55 \({}^{\circ}\)C, allowing it to be used in buoys on the waterway;
* Safety: LiFePO4, unlike its lead-acid counterpart, does not emit dangerous gases, and carries no risk of exposure to corrosive electrolytes;
* Its standard charging current of 10 A and discharge current of 20 A, as well as peak discharge current of 30 A, guarantee fast charging and efficient power supply of devices with high energy consumption. In the context of application in the intelligent buoy, the charging speed plays an important role (the battery can be charged immediately on the serving unit). As shown in Table 1, continuous power supply to the central unit will require frequent battery recharging. The battery replacement period is also related to the frequency of sending data from the central unit to the main server (current consumption max--Table 1). This operation additionally significantly discharges the battery. The power demand can be limited by hardware or software. The hardware method (e.g., using the Leonardo Module integrated with the GSM/GPRS/GPS SIM808 module selected for the system implementation in relation to Arduino with various GSM modules) allows for a maximum reduction in power demand by about 60% (Table 1). This is not sufficient. The possibility of software \"sleep\" of the Leonardo module was tested, while no measurements were taken and no data were sent (this was performed every 30 min). Internal Arduino libraries were used, allowing the controller to \"sleep\" in various ways. The tests performed showed that limiting current by putting the controller into \"sleep\" is effective, reducing consumption to about \(L_{\mathcal{C}}\) = 2 mA. The possibility of using a free analog channel in Arduino to measure the supply voltage and send this information to a remote server was investigated. The voltage value will determine the battery charge status. The battery discharges slowly in the first period of operation (a small voltage decrease--around 0.1-0.3 V), so that when it is close to discharge, the voltage drops significantly by 1-2 V (Figure 3). The use of a new, technologically advanced battery, combined with the development of energy-optimized software for the measurement unit, has extended its lifespan, reducing  
Figure 2: A damaged buoy taken from the waterway: (**a**) made of metal; (**b**) made of composites. the need for recharging to at least once a month. Maintenance work currently carried out by river service staff every 3-4 weeks (to oversee standard buoys) will be fully sufficient for replacing the battery as needed. * Central unit topology  
The entire system of the central unit is shown in Figure 4. Data collection from sensors located in the buoy is carried out automatically using an integrated system of sensor networks connected to the central unit using signal converters. The sensors are powered directly from the Leonardo board. Figure 4: Central unit topology. Figure 3: Time course of the discharge voltage of a LiFePO4 20 Ah battery with a discharge current of 400 mA.