Add function to read pH sensor

Add ability for the microcontroller to read data from the pH sensor.

DEPENDENCIES:
- Completed developed of a successful pH sensor.

Start by locating the microcontroller entry point and existing sensor-reading code in the System repository, then verify that the pH sensor development dependency is complete. Define the expected sensor data and validation path before implementation; done means the microcontroller can read and expose reliable pH sensor data.

Written by the indexing model from the issue text.