Pulse Width Modulation is one of the important functions of timer. PWM is a technique to control analogue circuits with digital output from microcontroller. As you all know that an Analogue signal is the one whose value varies continuously with time whereas digital signals can only be either high or low.
LM35 is an integrated-circuit temperature device with an output voltage linearly proportional to the centigrade temperature. As LM35 is not calibrated in Kelvin, user does not require to subtract large constant voltage from the output to obtain convenient centigrade scaling.