Low-Power E-Paper Weather Station
How to build a low-power weather station with off-the-shelf components? E-paper panels only require power to change the display and keep the display unchanged even powered-off.
The EPDK kit was sampled by Pervasive Displays.
The project is built around the Pervasive Displays E-Paper Display Pico Kit (or EPDK). It includes:
The low-cost CJMCU680 breakout board features the Bosch BME680 sensor. Compared the other members of the environmental sensors family like the BME280 (temperature and relative humidity) or the BMP280 (temperature, relative humidity and barometric pressure), the Bosch BME680 sensor features temperature, relative humidity, barometric pressure and gas, actually volatile organic compounds (or VOC) .
The measure of VOC is performed by a metal-oxide (or MOX) sensor and works like this: the higher the concentration of VOC, the lower the internal resistor; and the lower the concentration of VOC, the higher the internal resistor
I used a breadboard for easier configuration, and a second Raspberry Pi Pico RP2040 as programmer-debugger.
The project uses the Arduino SDK and dedicated libraries.
The Pervasive Displays Library Suite (or PDLS) provides all the graphic, text, configuration and update functions.
There are different libraries for the BME680. I tested the Zanduino BME680 and the Adafruit BME680 libraries. Unfortunately, the measure of gas seems to impact the measure of temperature, as the MOX sensor is heated to measure the level of VOC. As a solution, temperature offset could be calibrated.
Bosch also provides the Bosch Sensortec Environmental Cluster (or BSEC) library, albeit with pre-compiled archives. The version for the Cortex-M0+ works fine against the Arduino Zero but not against the Raspberry Pi Pico RP2040.
Off-the-shelf solutions make this project fast and easy to develop.
The Pervasive Displays E-Paper Display Pico Kit includes all the resources for the controller and the screen. The project reads the measures and updates the screen every 10 minutes, a good compromise between power consumption and up-to-date information.
The management of the screen is performed by the PDLS EXT3 Basic library for initialisation, font selection, text formatting, rectangle drawing, and panel update.
More advanced algorithms are required to take the most of the BME680 sensor, especially combining VOC level, temperature and humidity to calculate a more reliable air index.
A good alternative is the Bosch BMP280 without the VOC measure but with calibrated temperature, relative humidity and pressure.
Posted: 06 Dec 2021