Keller 36XiW-CTD

[neilh10]

data sheet at https://keller-druck.com/en/products/level-probes/multi-parameter-probes/series-36xiw-ctd
discussion on RS485 v SDI-12 implementation
https://www.envirodiy.org/topic/keller-ctd-sensor/

Practically Mayfly 1.0A3 doesn't have a working +12V, and hopefully the new version of Mayfly 1.x will have a power specification to the +12V so it can be matched to what the Instrument requires. EnviroDIY/EnviroDIY_Mayfly_Logger#33

Envirodiy RS485 status - https://www.envirodiy.org/topic/rs485-schematic/ and if it all works, its a very nice combination. 

However there are two other RS485's board with boost to +12V, one of which I've implemented https://github.com/EnviroDIY/Mayfly-Modbus-Wing/tree/master/knh002-MayflyWingShield  

The SDI-12 implemented on the Mayfly is a subset of the SDI-12 Specification. https://sdi-12.org/ .

A level shifter is needed - from out-of-spec 3.3V to specified 5V - and there has been a lot of discussion about the "Half-duplex"  level shifter elsewhere, which with the SDI-12 software is complex to get right.

The Mayfly software implementation for SDI-12 protocol doesn't include the CRC option, and the RS485 version has that implicitly built into. 
  #68 and need a SDI12 to do regression testing like https://vegetronix.com/Products/SDI-12-Sensor-Translator/ 

The Mayfly SDI12 subset is not protected from voltage (lightening, ESD) as per the recommendation in the spec. 

The knh002-MayflyWingShield  - supports SDI-12 and RS485.
The board has a prototype level shifter, but there was problems in software in making it work, so it is using the 3.3V levels.