The ECO-Box was initially designed with decoupled modules in a rapid prototyping fashion. It consists of several interconnected subsystems that can be implemented as separate modules or as a fully integrated custom device. For early prototyping and testing of different hardware configurations separated modules are favorable as they provide plenty flexibility to swap out various components. A fully integrated solution on the other hand moves many aspects of hardware modularity from assembly to the design step. It therefore enables easier and more reproducible setups resulting in faster assembly and deployment times. The right choice depends on whether you want to focus on experiments with different hardware setups or on the software side of custom sensing applications. Following sections give a brief overview of the most important hardware components.
The rest of this page guides through the individual hardware modules of the ECO-Box.
Sensing and Computation
Obviously the heart of an embedded sensing device is the microcontroller or MCU that runs the software and controls the sensor and communication peripherals. MCU manufacturers commonly sell evaluation boards that simplify connecting all sorts of external circuitry to allow for flexible testing in early development stages. This is exactly the kind of flexibility we want for a versatile sensing device. However, a downside of those boards is that they are often not suited for very low power operation because they are designed for prototyping and evaluation in labs instead of real deployments. Therefore extra care must be taken when selecting an eval board that will work with very low power consumption in real deployments.
We chose an STMicroelectronics Nucleo-L476RG board for that task. It comes with plenty connections for external devices including 76 Pins for the ST-Morpho connector and also the well-known Arduino compatible pinheaders. The part of the board that carries circuitry for flashing and debugging (ST-Link) can be easily removed to avoid any current leakage.
An SPS30 laser dust sensor is used for air pollution measurements of PM10, PM5, and PM2.5 particles. In earlier versions an SDS011 sensor was used which was replaced because of the better measurement accuracy, better longevity, and a smaller form factor of the SPS30.
Ambient temperature, humidity and barometric pressure are measured with the tiny environmental BME280 sensor.
A highly integrated Quectel L96 GPS module is used for low power Geo location via the satellite systems GPS, GLONASS, BeiDou, and Galileo.
There are always special use cases that require dedicated sensors. Additional hardware can therefore be easily connected via available SPI, I2C, and custom interfaces using plain analog and digital signaling.
Data Storage and Connectivity
Micro-SD cards are used as cost effective option for persistent local storage. This allows to perform data collection even in the most remote areas without any infrastructure or in event of network outages or poor coverage.
Long Range Radio Communication
For connectivity the ECO-Box employs a LoRa module based on the SX1276 giving it the ability to transmit live data even from remote locations. In previous deployments the ECO-Box was also used with 802.15.4 radio modules based on the Atmel AT86RF233.
The solar charger is a custom module based on the LTC3105 by Linear Technologies. It provides configuration options for output voltage and a maximum power point (MPP) setting to enable using different types of energy storage and solar cells.
With primary batteries having a finite capacity and cycles of rechargeable batteries being restricted, alternative ways for energy storage are needed for maintenance-free sustained operation. Simply put, a super capacitor overcomes this by storing energy physically instead of relying on a chemical process that is subject to degradation. It can therefore be recharged a lot more often and is very robust against environmental conditions. The downside is a significantly lower energy density that must be considered by the power management.
Self-Measurement of Power Consumption
The ECO-Box employs an integrated bidirectional shunt monitor to perform fine grained measurements of the charging rate and consumption of the system. Those power measurements are used as input for the adaptive power management.