Interface Temperature Sensor to ADC

Discussion in 'General Electronics Chat' started by circuit4pcb, Jul 1, 2013.

  1. circuit4pcb

    Thread Starter New Member

    Feb 4, 2013
    20
    0
    I would like some help interfacing LM35D temperature sensor to an ADC. I need the temperature reading to be from -40C to 180C. Please ingnore the fact it is only is rated to 150C. It appears from fingure 2 on the datasheet that all i need to do is put a pull down resistor at the output (with negative voltage) and then the calculation for the resistor will be R=-Vs/50uA. The range for the ADC is 0-2.5V.

    Now the problem I have is I do not have a negative voltage available. All I have is 2.5 and 5 Volts. How else can I get measure between -40 and 180C? My other alternative is to use AD590.

    http://www.biltek.tubitak.gov.tr/gelisim/elektronik/dosyalar/5/LM35.pdf

    Thanks
     
  2. bug13

    Well-Known Member

    Feb 13, 2012
    1,208
    38
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    Use an LM135 temp sensor calibrated in Kelvin 10mV/ K , so at -273C its zero volts, at 25C its 2980mV, 100C 3730mV ,150C 4230mV.
     
  4. circuit4pcb

    Thread Starter New Member

    Feb 4, 2013
    20
    0
    I am unsure how to do this. Every example in the datasheet claims 10mV per kelvin. I am still not real clear on this issue. please help

    Thanks
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Simply use two diodes and shift the voltage level.
    [​IMG]
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    To convert Kelvin to Centigrade subtract 273', so 273K = 0C

    the sensor at 0C will give out 2.73V, and -40C will be 2.33V , so if you put it into your A/D just alter the programme or Ref voltage to strip off 273,
     
Loading...