A thermostat is a controller that maintains a system's temperature near a fixed point. The simplest thermostat does this by switching a heater or AC on and off to maintain the desired temperature. The following model simulates a thermostat that uses a temperature sensor to control a heater. Turn on the temperature graph. Let the simulation run for a few cycles and then turn on the sunlight. Compare the behavior of the temperature graph. You can also try to move the temperature sensor to examine how the on/off time of the thermostat depends on its location.