Balboa GS523DZ

Some Balboa SPA controllers expose a RS-485 connection (to add on a Balboa Wifi module) which makes it possible to communicate with it. Then the following types of projects are a possibility:

https://github.com/ccutrer/balboa_worldwide_app/wiki

https://github.com/cribskip/esp8266_spa

The Balboa DS523DZ does not have any RS-485 from what I have understood, so we are left with two other options:

There is a connection for "Dolphin Remote" which seems to have some kind of SPI bus which could possibly be used:

https://www.olivierhill.ca/archives/72-The-Internet-of-Spas.html

The third option is to intercept the signal that goes between the mainboard and the display unit:

https://docs.google.com/document/d/1xuc5N6-Q7J7bQxBARYjUywhqkIFjOnh8vAHqEya5QAI/edit

https://www.raspberrypi.org/forums/viewtopic.php?t=175399

https://github.com/heisler3030/homebridge-spaberry

https://github.com/heisler3030/spaberry

https://docs.google.com/spreadsheets/d/1-Y5wH2sz1px8FiBiOiYuzq-N7vTPD8VZ9AVfSoYJa4Y/edit#gid=0

Big question is if I could hook into port J2 "in parallell" with the display to avoid putting an arduino in between the display and the control board.

The last resort is of course always to create your own SPA controller, compatible with the top panel:

https://hackaday.io/project/171003-openspa

It has some nice information on the protocol to the display as well: https://github.com/NickB1/OpenSpa/blob/master/documents/Balboa/Balboa_Display_Measurements.pdf