The FoliArduino system will record both air and soil temperature and humidity as well as the incoming shortwave radiation (visible and near infrared) at the tree level. The device will measure meteorological variables at a high temporal resolution of 15 minutes, but will also take pictures of the canopy every 30 minutes during the day.
Data are acquired using an Aduino Mega 2560 Rev3 board powered by a 6v 10Ah lead-acid battery. (I will check later for a solution to transfer the system to other Arduino board.)
The system is composed as follow (click on the title to be redirected to the dedicated page of each sensor):
- Power supply:
The system is alimented by a 12v 7Ah lead-acid battery which is charged by a solar panel. I describe in this section how to regulate tension for the FoliArduino system. The problem identified here concerns the solar panel. To save power, the system is controlled by an RTC clock that shutdown and wake-up the system to take measures every 15 minutes.
Data are acquired by an Arduino Mega 2560 Rev3 controller and stored on an microSD card. In this section I describe how to store data in an efficient way.
Air relative humidity, temperature and atmospheric pressure are measured with the BME280 module. The BME280 sensor also has the advantage to work in relatively extreme conditions and can be used to compute vapour-pressure deficit. In this section I describe how to install and code the sensor. For precise and low cost temperature measurement I also explain how to create a Type T thermocouple (constantan/copper) that has excellent repeatability and good accuracy.
Here I compared two types of soil humidity sensors, a modified resisitive sensor and a home made capacitive sensor. In this section I describe how to create and calibrate the two sensors. The soil moisture sensor is coupled to a waterproof temperature sensor (DS18B20). Humidity and temperature are measured at two depths, 10 cm and 50 cm.
I tested 3 amplified photodiodes with different spectrum sensitivity, both alone or in combination in order the have the best estimates of light intensity and quality. Those three diodes have already been used to create pyranometers in past studies and are the BPW-21 (Osram opto), BPW-20RF (Vishay) and the S-1223-01 (Hamamatsu). I describe in this section the different responses of each photodiode, and how to create and calibrate a low-cost and robust pyranometer for radiation measurement. The major problem identified here is the calibration of the sensor.
I tested two different camera sensors, the OV7670 CMOS image sensor (0.3MP resolution) and the OV2640 (2MP) camera module for Arduino. I describe in this section how to mount the two sensors and to store data on the SD card.
Not included yet:
- Precipitation sensor: For the moment only soil moisture will be measured with FoliArduino. Precipitation is not yet included because I identified a major problem with existing rain gauges, that is the need for continuous power supply for a robust measurement. It is not compatible with half-hour records and the Arduino sleep mode. I am working on an alternative low-cost rain gauge that can be used for robust discontinuous measurement.
- GSM communication: Data are currently stored on a microSD card. I am planning to add a GSM module to communicate data and to remotely check system integrity.