A simple and compact system for connecting a few low-cost sensors was proposed for an internal development project (RICE - Rapid Instrumentation and Control Environment) to continuously monitor an injection moulding machine. For flexibel wireless integration, the sensor readings, which are used as input for a ML model, had to be transmitted more or less in real time via different channels (WiFi/MQTT, Bluetooth LE/GATT and LoRaWAN).
A M5Stack TOUGH device was procured as test equipment and equipped with a few I2C sensors and a serial LoRaWAN module from M5Stack (ASR6501). Unfortunately, our device did not have an internal RTC backup battery. We placed an additional small LiIon cell (400mAh) in the yellow housing, which feeds the RTC if the USB cable is disconnected and as a bonus feature also enables autonomous operation for up to 90 minutes.
The initial sensor set consisted of a Bosch BME680 (temperature, humidity, IAQ, eCO2 and VOC), Sensirion SFA30 (humidity, formaldehyde) and Melexis MLX90614 (non-contact IR temperature sensor with 5° FOV).
To compile the wireless sensor hub firmware for the M5Stack TOUGH, which is based on
ESP32 microcontroller, download Visual Studio Code
and install the PlatformIO add-on.
Open the downloaded project directory and adjust the settings in include/config.h
to your needs. By default the sensor data is only published via WiFi/MQTT. Most
options can later be reconfigured under Setup in WiFiManager's
configuration portal (see section 'Initial Setup').
Note
Sensor readings from the BME680 are derived from Bosch's BSEC library. This partially precomplied library is only available for use after accepting its software license agreement.
Since the firmware was developed on a MacBook you probably need to adjust the upload port
settings
in platformio.ini. The M5Stack TOUGH device uses a
CH9102 Chip to connect
the ESP32 to USB. You might need to install additional drivers for your OS.
For firmware updates after the initial USB upload you can use the WiFiManager's OTA option.
On first power-up, the WiFiManager
will create the access point SensorHub-XXXXXX to configure device parameters
and to connect the M5Stack TOUGH to your local WiFi network. A random WPA password
is shown on its display. After saving the WiFi credentials, it will received an IP
via DHCP, which is displayed together with the WiFi RSSI at system startup.
When the M5Stack TOUGH has started to display sensor readings (see photo above), the BME680 sensor is still calibrating and no values for IAQ (air quality index), VOC (volatile organic compounds) and eCO2 (estimated value for CO2) are displayed. The first readings should show up after about 5 minutes with an IAQ accuracy indicator of 1 (value after slash). When the IAQ accuracy eventually reaches 3, after exposing it to clean and polluted air for 30 minutes each, the sensor is fully calibrated. It is recommended to initially run a new BME680 sensor for 48 hours to "burn it in". The automatically calculated calibration settings from the BSEC library are saved to flash every 2 hours and are reloaded when the M5Stack TOUGH is restarted. At device startup you have the option to reset the previously saved BSEC settings to recalibrate the BME680 sensor for a different environment.
In normal operation, when the screen with regularly updated sensor readings is displayed, you can restart the sensor hub by swiping horizontally from left to right across the touchscreen. When restarting, you will be asked whether youwant to start the local access point to reconfigure the sensor hub.
Pull requests are welcome! For major changes, please open an issue first to discuss what you would like to add or change.
Copyright (c) 2023-2024 Lars Wessels, Fraunhofer IOSB
This software was published under the Apache License 2.0.
Please check the license file.