lm35,opamp, pic16f877a

Discussion in 'The Projects Forum' started by thrza, Apr 6, 2009.

  1. thrza

    Thread Starter New Member

    Apr 6, 2009
    am currently doing my project in ece field. My project title is Automatic Infusion of Anesthesia using micro controller.
    Am using lm35 to sense the breathing temperature of the patient to calculate the breathing rate to be displayed on LCD.

    Can any one tel me how the use of opamp after lm35 will affect the results.

    Am displaying the no. of pulses per minute on LCD as to indicate the breathing rate. Acc to which the anesthesia will be infused to the patient.
  2. electronictech

    Active Member

    Apr 1, 2009
    The LM35 or LM34 are analog temperature sensors and they usually do not have a fast response time (IMHO not fast enough for a breath rate measurement derived from temperature differences).
    I've used an LM34 with an AVR (ATmega32), and I used the internal voltage reference of 2.56V (which is built in with the ADC) so that I would not need an op-amp in between the LM34 and the microcontroller for signal conditioning.

    May I suggest you use an 'anemometer' to measure the breath flow rate, or perhaps a pressure sensor that is connected to the breather tube. The pressure sensor would give you the fastest response times, increasing the reliability of your project, while the anemometer would give you volume of air being consumed per inhale/exhale.

    Anyways, have fun!
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    The professional measuring systems for doing research on athletes use a differential pressure gauge in the breathing tube. The sign of the difference voltage gives you direction and the magnitude over time gives you respiratory volume (unless the gear is made by one company I won't name here).

    It might be possible to use a thermistor in self-heating mode to get air velocity, but those critters are hard to calibrate.

    If this is for real, so to speak, don't forget that it all has to be intrinsically safe in an explosive atmosphere.
  4. thrza

    Thread Starter New Member

    Apr 6, 2009
    thanks for your suggestions on my project.