## 5 Platform Preparation for the Field Test
### Preparation of the Sensor Node for the Field Test  
The sensor node prototype described in Section 4.2 was designed for laboratory tests. It lacked several features for field tests, such as a temperature transducer, its interface circuit and a microcontroller input to read the transducer. Thus, the node schematic (shown in Figure 7a) was manually changed directly on the PCB, as shown in Figure 7b. R3 (an NTC) and R2 were connected as a voltage divider that was supplied only during the readings (to reduce node energy consumption) by reusing the SPI output pin  
Figure 5: The network is made of independent cells with a star topology inside (the distances assume a 200 m sensor communication range). The sensors in each cell are covered by two gateways, which can independently contact the server to ensure redundant field message aggregation and upload. Larger areas can be covered by joining elementary cells. Figure 6: The test field is about is about 195 \(\times\) 45 m (main body). Trees appear as darker spots on the light-colored soil. There are two gateways and 50 sensor nodes (round dots; some are placed outside the field due to GPS positioning errors). PB1 as a software-controlled voltage source. At the same time, PB4 was reconfigured as an ADC input to read the transducer, cutting its connection to the radio module (which was needed only for tests). These hardware and software changes allowed the sensor node to perform its main functions, monitoring the ambient temperature and notifying about abnormal high levels or too steep increases. The sensor nodes were programmed to measure the temperature once per second and to send specific alert messages when levels highly correlated with wildfires are detected. The sensor node has to support also a fast and error-proof field deployment procedure, as discussed in Section 3.1.3. Even if the field test was using just a few dozen sensors, it was worth defining and testing from the beginning an effective field deployment procedure suitable for large applications, with hundreds or thousands of nodes that are deployed by personnel with no special WSN training. These three items are especially important during the deployment of homogeneous sensors:  
1. the ID of the sensor node;
2. the quality of the reception of the sensor node messages by the gateways;
3. the field coordinates of the sensor node deployment spot. The node deployment procedure should minimize human input, because the operators may only have limited training and time. Thus, the automation of the procedure can significantly reduce deployment errors and cost. For an efficient field deployment, it is very important to be able to selectively address the node to be installed while other nodes are within comparable short distance (e.g., in the operator's backpack). Relying on the operator to input the node ID can be very time consuming and error prone, so an inexpensive (component cost and energy) near field communication with the node to install is necessary. For this purpose, we added a reedswitch in parallel with the NTC (see Figure 7b), which can be activated using a magnet from a distance up to about 2 cm. When activated, the ADC will read 0 V as the transducer output, which can be easily recognized, and temporarily switch the node to installation  
Figure 7: Schematic of the sensor node prototype for laboratory testing (**a**); issues fixed (**b**): (1) add a temperature transducer with an interface circuit and (2) add a means to switch the sensor to deployment mode. mode. In this mode, the node sends a few messages prompting the gateways in range to generate special acknowledgments that include the quality of the signal received from the node and the node ID. These data can be displayed on a handheld device to provide immediate feedback to the operator on the quality of the node installation position under evaluation. The handheld device can also determine the position of the node using an on-board GPS receiver and send all of the data to the server once validated by the operator.