This is a hobby and learning project.
Parts list:
- SenseAir Sunrise 006-0-0008 CO2 Sensor (€62 from DigiKey)
- ESP32C3 SuperMini dev board (€3 from AliExpress)
- Afafruit eInk Friend ($8.50 from Adafruit)
- 4.2" Waveshare eInk display (€33 from AliExpress)
- TPL5110 timer breakout board (€6 from AliExpress)
- Two resistors (220K and 1M) for measuring battery voltage
- A 3xAA battery holder (€ from AliExpress)
- A custom PCB to mount the above parts on
I experimented with other sensors, but ultimately picked SenseAir Sunrise because it has low standby power usage, has no warm-up time, and tolerates unregulated input current. It has good documentation too:
- Product Specification
- Handling manual
- Customer Integration Guidelines – includes sample schematics, power consumption stats, description of single/continuous measurement modes, description of calibration options
- I2C Protocol Docs
I found an Arduino library on Github that implements I2C communication with Sunrise, and got it to work with a couple small tweaks. My fork is here.
I bought the display on AliExpress, and am not entirely sure precisely what model I got, or what IC is inside. Adafruit's EPD library comes with different display drivers. I tried every driver until I found one that seemed to work.
Black/white displays are a better choice than tri-color displays, as they take significantly less time to refresh.
TPL5110 is a timer and power management chip. It turns on power every 5 minutes (the time period can be tweaked), and cuts power when the ESP32 sends an "I'm done" signal over GPIO. I am using it as a brute-force way of making sure there is no power drain between CO2 measurements (aside from the always-on power that the Sunrise CO2 sensor needs).
I designed the PCB in EasyEDA. There is a jumper on the board to switch between USB and battery power.
- Schematic as PDF
- Schematic in EasyEDA export format
- Board layout in EasyEDA export format
- Gerber files
I designed the case in Fusion 360. The case consists of three parts: the front part, a piece that the PCB and screen mounts on, and a backplate. The case snaps together with no screws. There is no transparent protective layer for the screen.
The Arduino sketch:
- reads sensor state from ESP32 flash
- reads battery voltage from ADC GPIO pin
- Measures CO2 level
- Writes the measurement to an append-only file on flash filesystem
- saves sensor state to flash
- displays CO2 measurement, battery level and measurement history graph on the eInk display
- sends a signal to TPL5110 to cut power
Here's how the UI currently looks:
