Arduino sketch that let you talk to your Calspa controller over I2C
Tested on an ATmega328P running at 3.3V/8MHz. Works on a 2012 Cal Spa with a Balboa controller CS6200DV. Other Balboa based controller with "dumb" Top Side displays might work.
Flash your chip with this sketch. You need to connect wires similar to this:
For more information regarding the pins, see the Cal Spa Connector
I use this setup with a WiFi microcontroller to monitor the hot tub remotely using MQTT.