## 2 Methodology and System Specifications
### Adaptation to Soil Instrument Idiosyncracies  
By inspecting the characteristics of the sensor selection presented in Section 2.1, it is inferred that they have quite diverse characteristics like different warm-up times and output types (i.e., analog or digital of more than one protocol). Furthermore, some of them can be marginally powered by a single microcontroller output pin, while others cannot provide accurate measurements this way due to the voltage drop on these pins as the drained current increases. This heterogeneity requires carefully designed data extraction methods.  
The application of the power-cycling method was selected for digital modules through the DDI operation mode, as it is the simplest way to trigger accurate measurements. Among the analog instruments, the output differs according to their model, requiring the application of different conversion formulas and potential voltage level adaptation to match the microcontroller digitizer specifications. The ability of the microcontroller to utilize a more stable voltage than the 3.3 V rated regulated voltage, i.e., a 2.56 V internal analog reference value, was a welcome option. In terms of power autonomy, although the soil instruments selected have comparatively low consumption, reducing the energy footprint of the whole node, the exploitation of the sleep mode capabilities of the hosting microcontroller was crucial for extending the node operation period from intervals of a few days to several months between battery changes. Added to this, as more than one instrument can be connected to the same node, during the node activity period each of them has to be switched on and off in a sequential manner to avoid power consumption peaks.  
The whole monitoring system should run for a long period and without human intervention while including sensing elements able to cover greater areas. The power requirements of each sensing node should be kept minimal in order to utilize conventional batteries; in the meantime, the use of small solar panels could offer welcome assistance wherever applicable. Thankfully, most of the soil measuring instruments of interest generate small amounts of information, while soil conditions do not change very rapidly over short periods of time. This application profile favors comparatively large intervals between consecutive measurements and low power, long range, and low rate-of-communication solutions, thus making protocols like LoRa very suitable against greedier solutions [27]. It is apparent that the abovementioned characteristics pose limitations to the microcontroller board options to be used for implementing the sensing nodes and may require additional components, like separate powering modules and/or signal multiplexers, to guarantee flawless measurement operation. The selection of the wrong microcontroller may lead to suspicious node behavior (i.e., to increased power consumption) and/or require the incorporation of more than necessary electronic accessories, further changing the size and the cost of the final product. The operating temperature and humidity specifications of all the participating components should also match the environmental conditions the IoT platform is expected to operate in.