Temperature sensor circuit

Discussion in 'The Projects Forum' started by vardy10, Jan 15, 2014.

  1. vardy10

    Thread Starter New Member

    Jan 15, 2014
    Ive been asked to design and test a prototype analogue circuit monitoring a variable of my choice. I will be using Pspice to simulate my circuit. I chose 'Temperature' to analyse as it is covenient within my workplace. I have to operate the circuit using a 5V DC power supply, and clamped to a range of 0-3.3V.
    This circuit must include an alarm of some sort i.e LED to indicate the variable exceeding a set limit, i.e max/min temperature.
    I dont have much experience in designing analogue circuits and would really appreciate some help on where to start. I am going to build my circuit using a breadboard.
    Will i have to use and IC within this circuit?

  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    I would suggest you decide on the type of 'analog' temperature sensor you plan to use on your project.
    The type you choose will depend upon the temperature range you wish to measure.

    Most analog temperature sensors will require some amplification so a OPA maybe required.

    Give us more information on the project specification.
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    Most often in school project like this. It is meant that you shall put together bits and bobs of what you have learned before. And use this to construct a circuit. Start by constructing the temperature sensor part. Ask your teacher if he/she has some preferred temperature sensor you could use. Is this project analog only, is it expected to use some kind of microcontroller
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    What is clamped?
  5. Richie121

    New Member

    Jan 12, 2014
    Clamped is usually referring to a type of voltage supply for the rest of your circuit that is kept 'clamped' at that set voltage regardless of how high the input is going, usually using a zener diode. Just look for regulated supplies and you will find plenty of examples.
    Your project sounds ideal to use a LM741 Op-Amp, and I've built something similar to turn a cooling fan on when things get too hot. You set a limit voltage on one input, and when a voltage crosses it on another input (from your NTC thermistor) something happens.
    Because you are comparing two voltages it helps to have a steady reference which is why you have been asked to supply it I think.
  6. NFA Fabrication

    Active Member

    Aug 12, 2012
    I often use am LM358 Op-Amp or an LM393 comparator for what you are doing. I use a basic thermistor inline with a resistor to make a variable voltage divider as one input and a potentiometer to make your set trigger voltage. And I often use this to trigger a re-triggerable monostable 555 timer circuit so I don't get relay chatter (Quick on/off's near the trigger temperature). I will often power the whole circuit with an LM7812 or LM7805 to stabilize the whole project depending on supply power.