Next, I replaced the Feather M0 board with an Adafruit Feather M0 Bluefruit LE (Overview | Adafruit Feather M0 Bluefruit LE | Adafruit Learning System). This Feather is nearly identical to the Feather M0, with the addition of a Bluetooth Low Energy (BLE) interface. The only change I needed to do to the wiring was to disconnect one pin (“DFU”) from ground, as this one now serves as a reset pin instead of a GND supply.
On my iPhone, I installed the “Bluefruit LE Connect” app (Installation and Setup | Bluefruit LE Connect for iOS and Android | Adafruit Learning System). There is also a version for Android. In addition, I installed on the PC a number of required BLE libraries.
Once everything was set up, I merged the Sensirion CO2-reading program with Adafruit’s example BLE plotting program, so I could plot the ongoing CO2 measurements on my iPhone. Here is another example of changes when I breathed on the sensor:
