Automatic temperature based exhaust fan controller
- 1. AUTOMATIC TEMPERATURE BASED EXHAUST FAN CONTROLLER ABSTRACT Saving of power is the main important criteria in the present world. In this project we are going to design the circuit to control the exhaust fan speed automatically according to the temperature in the room. Fan speed control is based on adjusting the voltage which gets to the fan. Fan speed control has been possible for many decades by using adjustable power resistors and adjustable transformers. Those methods have been used in movie theatres, houses and other public places. The problem of those controlling methods have been that they are big, expensive, have poor efficiency and they are hard to control from remote location. Electronics controlling also made possible to make them easily controllable from remote location. Solid-state speed controlling work by varying the "duty cycle" (on/off time) of the full AC voltage that is applied to the motor being controlled. For example, if the voltage is applied for only half of each AC cycle, the speed of motor will appear to be much less than when it get the full AC voltage, because it gets less power. A TRIAC is a 3 terminal ac semiconductor switch which is triggered ON when a low energy signal is applied to its Gate. Switching is fast. The low energy of switching means that a wide range of low cost control circuits can be used, for example, optically coupled switches. Since the TRIAC is bilateral (2 SCR's connected in opposite directions) the terms anode and cathode have no meaning. So the terms Main Terminal 1 and 2 (MT1, MT2) are used. It is standard to use MT1 as a reference point. The circuit controls the average power to a load through the TRIAC by phase control. The AC supply is applied to the load for only a controlled fraction of each cycle. The TRIAC is held in an OFF condition for a portion of its cycle then is triggered ON at a time determined by the circuit. In this project the motor speed will vary according to the room temperature. That means motor will rotate very slowly when the temperature is low and speed will increase as the temperature is increases. For sensing the temperature we are going to use thermistor. The output of thermistor is in the form of analog and that is given to ADC to convert it into digital form. The output of ADC is given to microcontroller and controller will set the firing angle depending on this digital value.