Sensor Box

The Sensor Box connects to the Adapter, the Spa Heater, and the two photocells. It contains the board for the temperature sensor and a board containing a humidity sensor and a board containing the humidity sensor and signal conditioning. It two 9-pin connectors: one for connecting to the Breakout Box, and another to connect to the Spa Heater and the photocells.
Here are photographs

Here are the circuit diagrams