This project provides the software to run a smart weather station with a small color display based on the popular ESP32 microcontroller.
- Measurement of ambient temperature, relative humidity, barometric pressure and lux
- Automatic time and date synchronisation over Wi-Fi specific to the configured timezone
- Automatic light and deep sleep
- Color display with three views:
- Welcome page
- Sensor dashboard with current readings
- Sensor history over the last 24 hours
- Last viewed tab is stored
- Automatic gamma-dimming over 15 s
The weather station uses the following sensors to measure environmental factors:
- BME280: Combined ambient temperature, relative humidity and barometric pressure sensor connected via I²C
- BH1750: Digital ambient light sensor connected via I²C
The sensor readings are displayed on a 128x160 pixel TFT color display based on the ST7735 controller connected via SPI and uses DMA to update the screen without additional CPU load.
The screens are created using LVGL v9.3 which can redraw subsets of the whole screen based on which widgets (temperature labels, animations etc.) need to be updated.
The Wi-Fi connection can be established by scanning the QR-code first displayed on the welcome screen of the display using the ESP SoftAP Provisioning App (Android, iOS) and selecting the desired Wi-Fi network. The credentials are transmitted encrypted via a temporary access point created by the ESP32 and stored in the internal flash. Consequently, the QR-code will no longer be shown and the Wi-Fi connection will be re-established after each power cycle using the saved credentials.
Please keep in mind that this is a hobby project and neither is the flash currently encrypted nor are the provisioning credentials secret or unique per device.
The LCD backlight is automatically dimmed over a parametrized duration using gamma fading. The backlight is turned on again and updated once the user short-clicks the push button. While the backlight is not fully dimmed off the user can change between the currently displayed screens by another short click on the push-button. This also aborts the fading and returns the LCD back to 100 % brightness.
Holding the push-button for seven seconds or longer will perform a factory reset after which the Wi-Fi credentials are lost and the QR-code will be shown again.
- Reset starts LP-core and triggers all tasks once
- Timer wakeup after CONFIG_SNTP_INTERVAL_HOURS triggers another SNTP sync
- GPIO wakeup from user button, sends sensor data to UI and triggers UI task
- LP-Core wakeup (currently unused, could be used for special sensor event)
- Pin mappings
- Usage of internal I²C and SPI hosts
- Refresh period of the sensors (default: once per minute)
- Server address for NTP time synchronisation
- Refresh period for NTP (default: 24 hours)
- Timezone including day-light-saving
- Implement averaging for correct 24 h history instead of 24 min
- Read sensors using LP core
- Sleep display and turn off backlight after n seconds of user inactivity
- Wake display based on button
- Wake-up repeatedly for SNTP sync
- Wake-up earlier if SNTP failed alst time
- Wake display based on proximity reading from time-of-flight sensor
- Deep sleep HP core
- Re-evaluate power usage with Firebeetle
- Measure air quality and/or CO2 content
- Check feasibility of Matter integration, e.g. with Google Home to provide a warning based on humidity and temperature thresholds
The software can be built and flashed using the ESP-IDF extension provided by Espressif.
The target hardware is the FireBeetle 2 ESP32-C6 which is a low-power IoT board supporting Wi-Fi, Bluetooth, Zigbee and Thread. The board can be powered using a 3.7 V Li-Po battery via the JST-connector. Charging is taken care of by an onboard IC while additional battery protection (e.g. overcurrent while discharging, undervoltage) must be provided externally.
The GPIO pins of the Firebeetle are connected as follows:
| GPIO-Pin-Number | Function |
|---|---|
| 1 | LCD Reset |
| 2 | User Push-Button |
| 6 | I²C data when LP-core is enabled |
| 7 | I²C clock when LP-core is enabled |
| 16 | LCD Chip Select |
| 18 | LCD Data/Command Select |
| 19 | I²C data when LP-core is disabled |
| 20 | I²C clock when LP-core is disabled |
| 22 | LCD SPI Master-out-Slave-in |
| 23 | LCD SPI Clock |
A 4.7k pull-up resistor should be placed on the I²C pin as well as the LCD reset pin.
Currently, the minimum power consumption is achieved when the LCD is faded off. The ESP32-C6 is then in light sleep mode, the LCD controller is sleeping (blank display). The low-power core wakes the high-power core every 60 seconds to update the sensor data.
When Wi-Fi is disabled FreeRTOS still runs a task for LwIP that periodically wakes up the processor causing current spikes.
The task can be suspended by acquiring the handle from the task name resulting in a lower current consumption.
The ESP can be put into deep sleep once the display is fully faded off and the SNTP sync is finished.
The measured 290 uA consist of roughly:
- 170 uA BME280 breakout board with on-board LDO and logic level shifting IC, compared to 0.1 uA sleep current according to datasheet (!)
- 100 uA ST7735 breakout board, compared to max. 45 uA according to datasheet
- 15 uA ESP32-C6 in deep sleep
- 5 uA BH1750 breakout board with on-board LDO and logic level shifting IC
Whenever the LP-core wakes up and triggers sensor measurements the current consumption is briefly slightly higher.
Further possible optimizations include:
- Aggregate sensor values in LP-core to avoid HP-core wake-up every measurement cycle