In this, I have designed a circuit to control the speed of a dc motor using the input from a Temperature Sensor(TMP36), BC547 NPN Transistor and a Zener diode(IN 4731A). The input from the sensor is calculated and that is converted as a PWM duty cycle and given as a PWM signal to the motor. If the temperature goes above the room temperature(fixed at 20-25 degree celsius), then the speed of the motor will increase (from 350 rpm upto 1200 rpm). If the temperature goes below 18 degree celsius(very cold), then the motor will automatically turn off. This is simple and doesn't involve the use of H-bridge to control the motor. This can be a model for the temperature controlled fan. If we could maximise this model, practically a temperature controlled fan can be designed which will run according to the room temperature. Climatic conditions vary. The temperature at 12 noon and 7 pm are not the same nowadays. if the room gets too cold, then the fan will automatically turn off. if it gets too hot, then the fan will automatically increase its speed.
