Adding LM35

Discussion in 'The Projects Forum' started by cikicikilala, Nov 7, 2010.

  1. cikicikilala

    Thread Starter New Member

    Nov 7, 2010
    hi everyone.. i have using PWM driver for a fan circuit (SgtWookie attachment) for my electronic project . how can i add lm35 temperature sensor into the circuit.. help me please.. give me solution. thank you.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. SgtWookie


    Jul 17, 2007
    The circuit I posted in the thread you hijacked ddn't use an LM35; it used a common 1N4148/1N914 switching diode for a temp sensor.

    You didn't post your PWM circuit, so we don't have any idea what to suggest to do to modify your circuit to add temperature compensation.
  4. Tahmid

    Active Member

    Jul 2, 2008
    I don't know about your circuit, but the way to do with LM35 is:

    The output of LM35 varies linearly in direct proportion to the temperature at 10mV/'C. So, you need to decide how you're going to reduce/increase duty cycle by reading the temperature-correspondent voltage.

    You could have a PWM circuit based on a PWM chip like SG3525, where the circuit increases/decreases the PWM depending on a trigger voltage.

    So you could have a comparator circuit reading the temperature or even multiples of circuits and increasing/decreasing the temperature as necessary by comparing against set-point voltages corresponding to temperature.

    You could alternately use a microcontroller which would do both the sensing and PWM parts and greatly simplify circuit design and complexity, although it would require expertise in the particular microcontroller.

    Hope this helps.
  5. wayneh


    Sep 9, 2010
    That's how I'd do it also. You may want to use an op-amp to amplify the voltage slope, eg. use a gain of 20 to give 200mV/°C. You could also use another op-amp to provide an offset, for instance to give 0v at 20°C.