Step 6:

Next, I wired up the fluid level sensor and wrote a program to convert the resistance measured in the sensor to the volume of container of fluid that it is submersed in.  If the fluid is full, the indicator LED will glow a soft yellow and the diffuser will operate normally.  However, if the fluid level is depleted to less than 10%, the indicator light will glow red and the diffuser will shut itself off and will not not turn back on until the fluid levels are returned to full.