platformio.ini should look something like this:
[env:mayfly]
monitor_speed = 115200
board = mayfly
platform = atmelavr
framework = arduino
lib_ignore = RTCZero
build_flags =
-D MQTT_USERNAME=YOUR_USERNAME
-D MQTT_PASSWORD=YOUR_PASSWORD
-D MQTT_CLIENT_ID=YOUR_CLIENT_ID
-D THINGSPEAK_CHANNEL_ID='"1851144"'
-DSDI12_EXTERNAL_PCINT
; DEBUG OPTIONS:
; -DNEOSWSERIAL_EXTERNAL_PCINT
; -D STANDARD_SERIAL_OUTPUT=Serial
; -D DEBUGGING_SERIAL_OUTPUT=Serial
; -D DEEP_DEBUGGING_SERIAL_OUTPUT=Serial
; -D MS_LOGGERBASE_DEBUG
; https://github.com/EnviroDIY/ModularSensors/commit/cc9a66edb4d0576c6e3f0d15e908876d30224879
; -D MS_DEBUGGING_STD
lib_deps =
EnviroDIY_ModularSensors
vshymanskyy/TinyGSM@^0.11.5
Data published to: https://thingspeak.com/channels/1851144
config.txt should be in the root directory of the sd flash card and look like this: { "storm_start_time": 1668100500 }