# A Low Power IoT Sensor Node Architecture for Waste Management Within Smart Cities Context
## 4 Node Architecture
### Switching and Powering System for LoRa Module  
The Switching and powering system for LoRa is in charge of properly supplying the LoRa transmission module (see Figure 5: for the sake of clarity, also additional blocks strictly related to the functioning of the one described in this subsection are included in the picture). Indeed, while Block A of Figure 4 provides the node with 5 V, that are needed for running the ATmega328, the LoRa module would be permanently damaged if fed with such a voltage due to the fact that it requires only 3.3 V. This task is fulfilled by the MC33269T voltage regulator produced by ON Semiconductor (Phoenix, AZ, USA). Moreover, this block is provided with an N-type MOSFET controlled by the ATmega328. This means that the latter is capable of switching on and off the voltage regulator, and consequentially the LoRa module, depending on when it is strictly needed (i.e., only during the transmission phase). This expedient allows further energy saving as it will be shown in the energy-saving policy Section 5.1. Likewise as it was in the previous subsection, the MOSFET is exploited as a bare switch controlled via firmware by the microcontroller by means of one of its digital outputs: once the filling level is measured, then the ATmega328 raises the logic level of the digital output connected to the gate of the MOSFET, leading to its saturation, which runs the voltage regulator allowing, in turn, the activation of the LoRa module and the transmission of the sensed data.  
Figure 5: Diagram of the Switching and powering system for LoRa block.  
The MC33269T is a linear 3.3 V voltage regulator which was installed as recommended in its datasheet [72]. Indeed, it requires two capacitors that act as low pass filters: a 330 nF plastic film capacitor (i.e., \(C_{I}\)) and a 10 \(\,\mathrm{\upmu F}\) electrolytic one (i.e., \(C_{O}\)). Still according to the datasheet, it has a dropout voltage of 1 V and since its input voltage is directly provided by Block A, hence the input voltage is 5 V, no supplementary problems arise during the supplying of the LoRa module.  
On account of the list of benefits offered by Pololu-like regulators (or generally by switching regulators) presented within the last subsection, one could wonder why such devices were not exploited as a regulator for the LoRa module too. For sure, a component like those would have been extremely effective from the energy-saving point of view. However, they are quite expensive (the price of the Pololu D24V22F hovers around 8 euros) and since one of the goals of the design of this IoT node is the cheapness of the node itself, then a cheaper voltage regulator (i.e., the MC33269T whose cost hovers around 0.7 euros) has been chosen even though it is not as efficient as the step-down ones: as it was explained in Section 4.4, the MC33269T has a higher consumption than the Pololu D24V22F5. Despite this, the overall energy requirements of the IoT node do not experience significant increase since (as it will be shown in Section 5.2) the MC33269T has a shorter running time than the Pololu D24V22F (thank to the energy-saving policy, see Section 5.1).