Hi Gabriela,
The bytes you need to send are documented here: ['L' 1] to start logging, and ['L' 0] to stop logging.
Each state can send one byte by default in output actions: {'AnalogIn1', B} where B is the byte you want to send.
So one (hacky) option is to use two states.
You can make it cleaner by programming the state machine's message library. This allows you to program each byte to equal a string of up to 3 bytes - so before building your state machine you'd use:
LoadSerialMessages('AnalogIn1', {['L' 1], ['L' 0]});
Then, trigger start and stop as messages 1 and 2 using output actions: {'AnalogIn1', 1} to start and {'AnalogIn1', 2} to stop.
FYI we know this is an awkward way to send byte strings. In our next software and firmware update (we hope to release by January) you'll be able to skip LoadSerialMessages, and simply use paste the byte string you want to send into the output actions, e.g. {'AnalogIn1', ['L' 0]} However, use of LoadSerialMessages will still be available for backwards compatibility.
I hope this helps
-Josh