How to interface a K type Thermocouple with microcontroller?

Hi all,
I want to interface K-type thermocouple with microcontroller. I am confused where to start with as thermcouple output voltage is in some micro volt. So i think i have to connect an amplifier with the thermocouple rather directly connecting it with ADC.My questions are:
1. How to choose an ADC for it (I want interface the ADC with SPI).
2. How to choose an Amplifier.

Hi,

The easiest way may be to just do a forum search "thermocoule microcontroller"... you will find a lot of useful threads..usually they will give you all answers.


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Or decide all on your own:

You begin with the wrong questions, they come later..

Begin with:
* What temperature range do you want to measure? (min, max)
* what temperature resolution do you want?
* how often per second or per hour do you want to measure? (conversion rate)
* are you able or do you want to calibrate the temperature measurement?
* what absolute temperature error do you need?

--> With the temperature range you can find out the thermocouple voltage range.
--> with the temperature resolution resolution you find out what ADC resolution you need.
...decide what supply voltage you want to use for microcontroller and ADC.
--> with the conversion rate you now can choos an ADC (additinally look for: price, availability, interface...)
--> then find out the input voltage range of your ADC

Divide ADC_input_voltage_range / thermocouple_voltage_range ... and get the amplifier gain.
Calculate what the absolute temperature error means for voltage_error.
Select an OPAMP with less offset_voltage than this voltage error.

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Klaus

I used this schematic in one of my projects. Works pretty well. But requeres s/w callibration and cold junction compensation. +\- 3*C you will have.