# 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
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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

Feb 13, 2012
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3. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,154
772
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
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Simply use two diodes and shift the voltage level.

6. ### Dodgydave AAC Fanatic!

Jun 22, 2012
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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,