Flashing of the firmware is most easily achieved using the Arduino IDE, which may be downloaded from . It is also necessary to download and install Teensyduino () for compatibility with the Teensy 4.0. Flash the firmware by opening the firmware file "FluorescenceSensor.ino" within the Arduino IDE, connecting the device via a USB cable, and clicking the "Upload" button within the Arduino IDE. Once flashed, the microcontroller will output the measured lock-in amplitude 𝑅 2 at 0.1-s intervals, which can be read using the Arduino IDE's serial monitor, or using the software front-end described below. Typically, it takes several minutes for the output of an LED to stabilise after initial switch-on, and we recommend waiting at least 15 minutes before beginning measurements.