Is it time to water the plant?

This activity is an introductory way to use sensors, physical computing and a program on a TI calculator to determine if a plant needs to be watered. The program reads the soil moisture value from the moisture sensor (through a TI-Innovator Hub) and compares the value to thresholds for "dry soil". If the moisture sensor value is lower than the dry threshold, the program prints a message to the screen and changes the color of the RGB LED on the TI-Innovator Hub to RED. If the value is higher than the dry threshold, the program prints a different message to the screen and changes the RGB LED color to GREEN. The program can be extended to have a "need to water soon" message with a YELLOW light if it is between two set points. Extensions:
This simple check of the soil state can lead to some additional questions to discuss when doing this activity.

1. Instead of watering everyday at a fixed time, we should use this to only water when needed. Maybe we are watering too much? Or too little?
2. Different plants will use the water at different rates. We could have different watering times based on how dry the soil is.
3. Do different soil types hold water differently? How does the outside flower bed differ from the indoor plants?