Energy saving by automatic control of power in simple home appliances

This system saves energy by efficient power management of a room which employs certain controlling mechanisms managed by a microcontroller. The mechanisms include light control relative to the natural light intensity in the room, fan control relative to the room temperature and motion detection for determining absence of occupants in the room. The MCU reads light intensity level from an LDR voltage divider circuit. If the natural light intensity is below the preset threshold value then the lights are turned on and vice versa. Room temperature readings are taken from an Lm35 sensor and compared with the user defined threshold value. If the readings are above or equal to the threshold value then the fans run at full speed. If it is six degrees or more below the threshold the fans are turned off. At intermediate temperatures the fans run at intermediate speeds. Fan speed is controlled by changing the voltage level across them using triacs which avoids the I²R losses of potentiometer regulators. Motion detection is achieved by using a PIR sensor. If the room stays unoccupied for a preset amount of time the loads are turned off to prevent wastage. Lastly, the user defined thresholds are changed using a keypad.