2. Sensors Selection in Respect of Measurement Accuracy of Physical Parameters
We have developed our prototype with the aim to use it in a traditional naturally ventilated single-sloped greenhouse, considering the environmental conditions data collected by Hua et. al  in a measurement campaign in order to validate their deterministic and stochastic model for estimation of greenhouse microclimate. In particular, in this kind of greenhouse there is a daily variation temperature in the range between 10 °C to 40 °C and a daily relative humidity (RH) from 10% to about 90%. As a matter of facts, our electronic platform has been designed to guarantee best performances in these environmental conditions. The board permits to collect a set of measurements of the main greenhouse environment parameters, with an accuracy reported in Table 1, according to data collected by Hua et. al. On the basis of these specifications, for each physical parameter can be chosen a sensor for performing measurements, from the analysis of the state of art.
|Physical Parameter||Measurement Accuracy|
|Air temperature||0.1 °C|
|Air humidity||1% UR|
|Solar radiation||5 W/m2|
|Air velocity||0.1 m/s|
3. Methods: Design and Development of the Electronic Board
A 3D view of the board with its modules integrated in the Main Board, is shown in Figure 2. Each module has been descripted in the following sub-sections.
In order to allow on-site use, a dedicated box has been designed, using an appropriate CAD, to protect the board from environmental agents, such as weather conditions, fertilizer emission, intrusion, dust, accidental contact and water. For these reasons, the development of the box has respected the IEC standard 60529-IP56 . The box has six holes (one for power supply, one for Ethernet port and four for external sensors) in order to permits connections between board and sensors, power supply and internet gateway. For assembling the board on the box, four 5-mm diameter rounded turrets have been designed and positioned on each box angle. The box size is 172 × 192 × 110 millimeters.
Figure 3 shows a 3D view of the box.
3.1. Green House Core (GHC)
The Green House Core module contains the core of the board and consequently it permits to manage all modules intended to data acquisition and communication. In particular, 8-bit Atmel ATmega2560-16AU microcontroller (Table 2) has been chosen . We have selected an 8-bit platform, instead of a more recent 32-bit platform, as well as for the economic aspect, for the following main reasons [34,35,36]:
|Maximum clock frequency||16 MHz|
|Flash capability||256 kB|
|CPU speed||16 MIPS|
|Timers/Counters||2 × 8-bit, 4 × 16-bit|
|Temperature range||−40–85 °C|
|Voltage supply||4.5–5.5 V|
|Max Current supply||14 mA|
- The majority of 8-bit devices are proposed in DIP packaging. This aspect makes them easy to plug into a breadboard and get starting with the prototype experiments, guaranteeing a fast and easy solution.
- Most 8-bit devices run on 5 volts, as well as the ATmega2560-16AU microcontroller. 5-volt systems provide better noise immunity and the majority of industry standard modules use 5-volt logic levels, as you can see from most of selected chips of our board.
- 8-bit devices are robust and it results harder to damage an 8-bit device than a 32-bit device .
- The use of an 8-bit device guarantees a low and fast learning curve as concerns the firmware development .
- Many modern microcontrollers incorporate some hardware functions that serve to help the CPU operate as efficiently as possible, such as the Peripheral Event System, which allows peripherals to interact without intervention from the CPU. In the case of detecting a hardware event, it is important to first detect the event and then switch control to the desired interrupt service routine (ISR). In these situations, CPU speed isn’t the single determining factor. It is a question of how long, in terms of cycles, does it take to respond to the interrupt, run the ISR, and return. As shown in Table 2 of , 8-bit devices can be more efficient in handling hardware near actions. In fact, the average clock cycles employed in an 8-bit MCU are lower than 32-bit MCU (i.e., for detect interrupt, jump to interrupt vector, return from interrupt, etc.).
3.2. Wi-Fi Module
|Transmitting/Receiving frequency band||ISM, 2.4 GHz|
|Transmitting/Receiving rate||20 MHz|
|Output power||20.6 dBm|
|CPU speed||16 MIPS|
|Communication protocols||SPI, UART, I2C|
|Flash memory||4 Mb|
|Voltage supply||1.8 V, 2.5 V, 3.3 V|
|Max Current supply||269 mA|
|Temperature range||−40–85 °C|
Since the maximum voltage supply of this chip and also its communication signals have a voltage equal to 3.3 V, a voltage stabilizer and a level shifter have been used for adapting 5 V to desired voltage of 3.3 V. As well as the GHC module, three LEDs (i.e., red, yellow and green) have also been inserted in the Wi-Fi module, for noticing the state of the module during firmware testing and developing phase. Figure 5 shows front side and back side of the 3D Wi-Fi module.
3.3. RS485 Module
|Communication protocols||RS422, RS485|
|Data rate||40 Mb/s|
|Number of receivers||1|
|Receiver delay||20 ns|
|Number of transmitters||1|
|Transmitter delay||15 ns|
|Maximum number of transceivers on the bus||128|
|Voltage supply||4.75–5.25 V|
|Max Current supply||2.5 mA|
|Temperature range||0–70 °C|
3.4. ADC Module
|Sampling frequency||3.3 ksps|
|Input channels differential (single-ended)||2 (4)|
|Number of transmitters||1|
|Voltage supply||2.0–5.5 V|
|Max Current supply||150 uA|
|Temperature range||−40–125 °C|
3.5. USB Module
|Data rate||12 Mb/s|
|Voltage supply||−0.5–6.0 V|
|Max Current supply||24 mA|
|Temperature range||−40–85 °C|
3.6. Main Board
The Main Board hosts the other modules (the GHC module, the Wi-Fi Module, the RS485 Module, the ADC Module and the USB Module) and guarantees power supply, filtering and protection to each of them thanks to Power Supply Unit (PSU) module (see Figure 1). Since one of the aims of the board concerns prototyping firmware and software in order to make the most of device performances, the Main Board has been designed without any strict electrical connection between various modules hosted (see Figure 9). In this way, it is possible to connect various modules as needed of the firmware and software developer (input/output ports selected, timer, pin optimization, etc.), which should program the board using an In Circuit Serial Programming (ICSP) interface. The board is 12–32 V powered and it provides, thanks to on-board DC converter , two different voltages, 12 V and 5 V, according to needs. In fact, the other modules are developed to operate with a 5 V power supply, whereas all sensors could be fed to 5 V, 12 V and 24 V power supply [24,25,26] and [28,29]. A power consumption calculation has been done in order to evaluate the maximum power supply for each module and consequently the maximum power consumption of our electronic board. In the calculation, the power consumption of outline electronics, such as resistors, capacitors, etc., is considered negligible compared to main modules consumption. The calculation is obtained considering maximum current (Imax) and voltage (Vmax) supply, in the worst case, of every chips involved in the board, using the following formula:
where m is the number of modules involved in the prototype. In Table 7, the maximum Voltage supply (Vmax), the maximum current supply (Imax) and the maximum power supply (Pmax) for each module are reported. Using the previous formula, the maximum power consumption of our prototype is equal to about 1619 mW. Since the board is 12 V–32 V powered, we have also calculated the energy consumption for each voltage, with the following formula:
Table 7. Power consumption calculation.
|Module||Chip||Maximum Voltage Supply|
|Maximum Current Supply|
|Maximum Power Consumption|
Consequently, the energy consumption decreases when the Voltage powered increases.
4. Results: Prototype Realization and Dedicated Firmware and Software Development
4.1. Development of the Dedicated Firmware
In order to investigate the stability of the acquired data and the results of the data elaboration using the UKF, we have tested the board during a time acquisition window of 30 s. The experiment has been studied with the goal of simulating a typical use scenario of the board. A resistive potentiometer has been powered by the board with a voltage of 5 V, and its voltage reading has been stored and elaborated using the UKF by the board. We have decided to test the board for voltages reading between 500 mV and 2000 mV, that are typical values of commercial sensors. In Figure 13 are shown the graphical results of the experiment.
4.2. Development of the Dedicated Software and Web Application
5. Discussion and Conclusions
Conflicts of Interest
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