There is a bug with the uart.sendbreak() method with V1.17 (haven't checked the latest)

The manual states the break signal lasts 13 bits. It actually is 11.
This has caused errors with external sensors that utilize the SDI-12 protocol. .The line needs to go for at least 12ms. Now, it is 9.167 ms. Even 13 bits is not long enough.
A good solution is to add a property where you can specify how many bits you can use.
SDI-12 is popular in agriculture and other industrial applications. (www.sdi-12.org)