ESP32 Arduino Setup
NOTE: The following instructions are only needed for the ESP32 + Reflowduino32 method! If you are using the traditional Reflowduino board you can ignore this.
The ESP32 is a bit different from traditional Arduino-compatible boards in that you can't just add it in the boards manager and have it working right away. Fortunately the setup isn't hard but it warrants its own section on how to do this as it might be a bit tricky for some people.
For more information about the ESP32 and its Bluetooth functionalities, please see my ESP32 BLE + Android + Arduino IDE tutorial!
The first thing you need to do is install the ESP32 package for Arduino IDE by following the Windows instructions or the Mac instructions. I will say that for Windows when the instructions tell you to open "Git GUI" you have to download and set up "Git" from the link provided and if you have a hard time finding an application called "Git GUI" then all you need to do is search "Git GUI" in the start menu and you will see a little command prompt-ish looking icon (see attached screenshot above). It's also located in "C:\Program Files\Git\cmd\git-gui.exe" by default. From there, follow the instructions and you should be good to go!
In Arduino IDE the first thing you should do is go to Tools / Board and select the appropriate board. It usually doesn't really matter which one you choose, but some things might be board-specific (typically the GPIO numbering and things like that) so watch out! I chose "ESP32 Dev Module" for my board. Also go ahead and choose the correct COM port after connecting the board to your computer via the USB cable.
In order to check if the ESP32 installation went well, go to File / Examples / ESP32 BLE Arduino and you should see several example sketches, like "BLE_scan", "BLE_notify", etc. This means everything is set up properly in Arduino IDE!
Now that Arduino IDE is all set up, test if it's really working by opening the Blink example under File -> Examples -> 01.Basics -> Blink and change all instances of "LED_BUILTIN" to "2" (the default GPIO number that controls the LED on the DOIT ESP32 dev board). After uploading the sketch you should see the blue LED blinking every second. Now you're ready to upload the Reflowduino32 demo sketch as described in a subsequent section!