## 3 Communication in IoT
### Commonly Used Sensors for Smart Farming and Heavy Metal Identification
This approach is used to detect the amounts of nitrate and sulphates by correlating the impedance of the sensor array with their concentration. The key approaches to soil macronutrients include electrochemical, VIS-NIRS, and ATR spectroscopy [149; 152; 156]. These approaches to soil macronutrients are limited to sensing a single desired ion because the membrane used in these methods only reacts to one ion [157]. To achieve a simultaneous multi-ion sensing, it is necessary to build a detector array for the sensing of soil macro nutrients [158]. There are several opportunities to advance the state of precision farming through the utilization of the above discussed sensors. The following Table 2 summarizes the list of sensors along with their functionalities which can be widely utilized in the field of precision agriculture. \begin{table}
\begin{tabular}{c c c} \hline
**No. \#** & **Sensor Name** & **Functionalities** \\ \hline
1 & ECHO 10 HS soil moisture sensor & Soil temperature, soil moisture, conductivity \\
2 & ECHO EA10 & medium-textured soil types with low EC conditions \\
3 & ECHO EC5 & Soil moisture probe \\
4 & GreenTag (RFID) & Soil moisture, soil temperature, heavy metal detection \\
5 & 5 TE Sensor & Water content, conductivity, temperature \\
6 & Hydra probe 2 & Soil moisture, electrical conductivity, dielectric constant \\
7 & MP406 Soil moisture sensor & Soil temperature, soil moisture \\
8 & MIKROE-1630 & Gases detection, air quality check \\
9 & Pogo II VWC sensor & Soil moisture and temperature sensor \\
10 & PXRF Sensor with VNIR & Supports on-site heavy metal detection along with soil moisture and temperature measurement \\
11 & NixPro Sensor & Soil color analysis which is coupled with dedicated soil scanner App \\
12 & Portable Electrochemical System (PES) & Supports on-site heavy metal detection \\ \hline \end{tabular}
\end{table} 
Table 2: Sensors used in the agriculture domain. WSNs typically consist of a large number of nodes that run in a particular configuration. Usually, autonomous and spatially dispersed sensor nodes collaborate to track and collect environmental conditions. Data can be processed in central/decentralized mode by sending data to a sink that transfers them to other networks (e.g., through a gateway). A broad variety of application-specific limitations is included in the project, design, prototype, and use of a WSN. The BTnode is a Bluetooth-based radio module and microcontroller for autonomous wireless communication [159]. BTnode is equipped with general purpose interfaces which can be configured on the basis of application specific requirement. BTnode can be utilized with several peripherals, i.e., sensors, actuators, RFID, and GPS receivers. A promising factor of BTnode is its compact size of 6 \(\times\) 4 cm with standard wireless interface. A pictorial description of BTnode is shown in Figure 6. The device comprises an Atmel ATmega128L microcontroller with on-chip memory and peripherals [160]. The microcontroller demonstrates an 8-bit RISC core delivering up to 8 MIPS at a maximum of 8 MHz. The on-chip memory comprises a programmable in-built 128 KB of flash memory along with 4 KB of static RAM. Other integrated peripherals consist of JTAG for debugging, timers, counters, pulse-width modulation, and 10-bit analog-to-digital converter.