Epiphyte Electronics: First Progress Report

I have started working with the electronics that will be needed to support Epiphyte, the first DAC project to be supported by CarbonCrowd. Epiphyte will be a scaled-down, open-source spinoff of Octavia’s Thursday DAC machine, and will be built in the undergraduate lab of the Chemical Engineering Department at the University of Pennsylvania. It is hoped that this effort will be an educational benefit to the students, as the Epiphyte will stay in the lab as a resource for education and research.

The Epiphyte will contain fans, heaters, valves, pumps, a lot of metal ducts, and of course a sorbent panel. It will also need to control these elements as well as to gather data from a number of sensors of various kinds, to measure CO2 concentration, temperature, pressure, etc. Hence, it needs a computer such as a microcontroller and a system for connecting all these devices.

I have selected for the controller the ESP32, which contains a powerful processor with built-in WiFi, Bluetooth, and a variety of interfaces such as I2C, SPI, UART, and several GPIO pins which can serve as analog inputs and outputs. This processor is available from Adafruit conveniently mounted on a small board (in Adafruit’s standard “Feather” form factor), with all the necessary connectors, regulators, etc. included. It has a USB-C connector for programming and powering it, and it can also be powered from a LiPo battery to operate autonymously.

Adafruit also sells a great variety of sensors and other useful devices, conveniently mounted on “breakout” boards so systems can be easily assembled with a minimum of soldering and risk of damage. Most of these have a standard connector called “STEMMA QT” or “Qwiic” (by Sparkfun) for providing power and I2C interconnections.

To begin work on developing the electronic control and monitoring system for Epiphyte, I placed an order from Adafruit for the first batch of parts. The entire order arrived in 30 hours, with standard shipping.

After soldering a few headers onto the boards, I assembled and programmed a setup to read two Sensirion SCD30 CO2 sensors. These are available from Digikey for $61.79 as the bare module, but Adafruit sells a breakout board for $58.95 with the sensor already mounted on a board for durability and with STEMMA QT connectors included. I also needed an I2C MUX because the SCD30’s share an I2C address; an LTC4311 I2C Extender for longer cable runs, and an OLED display.

The entire setup is shown below; after some programming, I got it to continually read CO2 and show the readings on the display:

The SCD30 also reads temperature and relative humidity, which are output on the serial monitor of the Arduino IDE:

As a fun experiment, I put one CO2 sensor outdoors, and one indoors to compare the readings:

Next up: Adding thermocouples.