#### mahdiiust

##### Junior Member level 1

Hi

I want to build a thermometer using pt100 and atmega8 microcontroller. First I build a 1mA current source using op07cp and connect it to pt100. Then I read the voltage of pt100 using atmega8 ADC and calculate the resistance. After that by some equations mentioned in pt100 datasheet the temperature will be available (of course in theory!!)

But I encountered a problem. The resistance variation for 1°C increase in temperature is about 390 mΩ. for I mA current and accuracy about 0.1 °C the voltage will be 39 µV. but I can’t read this voltage by atmega8 ADC (Vref=1.2 V, 10 bit). So I try to amplifying it using op amp. Is my scheme true? And which op amp is suitable for amplifying such low voltage? I try Ua741, op07 and LM358 but they didn’t work.

thanks

I want to build a thermometer using pt100 and atmega8 microcontroller. First I build a 1mA current source using op07cp and connect it to pt100. Then I read the voltage of pt100 using atmega8 ADC and calculate the resistance. After that by some equations mentioned in pt100 datasheet the temperature will be available (of course in theory!!)

But I encountered a problem. The resistance variation for 1°C increase in temperature is about 390 mΩ. for I mA current and accuracy about 0.1 °C the voltage will be 39 µV. but I can’t read this voltage by atmega8 ADC (Vref=1.2 V, 10 bit). So I try to amplifying it using op amp. Is my scheme true? And which op amp is suitable for amplifying such low voltage? I try Ua741, op07 and LM358 but they didn’t work.

thanks

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