PWM Fan Controller using PIC12F675 microcontroller

PWM Fan Controller

You can see the PWM Fan Controller project here.

The heart of the PWM Fan Controller is a PIC 12F675 microcontroller. This microcontroller is reading the analog output of a LM35 temperature sensor using a ADC (analog to digital converter) . The resulting digital value is converted to a temperature and a fan is powered proportionally to how hot the sensor is. The sensor is mounted against the hard drive chassis so it is measuring the actual drive temperature and not just the air temperature inside the housing.

Fan Controller

PWM Fan Controller – Parts

PWM Fan Controller – LM35 Sensor Overview

The LM35 temperature sensor package being used is the TO-92, it is small enough for this project and is leaded so that we can easily connect it to some wires. It is also nice since we can extend it by simply plugging it into a 0.1 inch female wire harness. This is a Celsius device and since the output is 10mV per degree it is very simple to calculate the temperature. It is even nice and simple to directly view the temperature on a multimeter as can be seen in the video.

PWM Fan Controller – Reading Data with the Microcontroller

The LM35 outputs 10mV per degree Celsius, this can be read very easily on the meter but unfortunately is isn’t quite that simple to read it within the microcontroller. The output of the LM35 is connected to an ADC (analog to digital converter) so that we can get a usable reading from it, but first we need to do a small calculation.
The analog input has a range of 0 to 5 volts and the digital resolution is 10 bits. This means that the 0 to 5 volt range will be represented by a number from 0 to 1023 in the microcontroller. If we divide 5 volts by 1024 we get the number of volts per digital increment. In this case it is 0.004883 volts per increment. So if the voltage was 1 volt on the microcontroller pin we would expect to have a reading of around 204 as the digital number (1/0.004883).

READ  Automotive Voltage Monitor using PIC12F683

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Current Project / Post can also be found using:

  • trouble free unless the 126842
  • pic 12f675 2light 1 fan
  • pic pwm fan
  • PIC12F675 dev kit

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