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I've tried a few options for reading the signals from thermocouples over the years.

The cheapest way (component cost) is likely to be DIY, and a lot of work involving lots of analogue stuff that I'm not good at!

I've tried the following:

MAX6675

1+     £14    
25+    £9    
100+   £5
  • SPI Thermocouple solution
  • Very easy to use and results are returned with 0.1°C accuracy.
  • Very expensive

AD597

1+     £6   
10+    £4   
100+   £3
  • Feed output voltage into microcontroller ADC
  • I've had good results with these

Does anybody have any other recommendations?

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  • \$\begingroup\$ Should this question be community wiki? Nothing is actually asked and I don't see how there can be one correct answer. \$\endgroup\$
    – AndrejaKo
    Commented Feb 9, 2011 at 20:02
  • \$\begingroup\$ The question appears to be, "are there alternatives to the MAX6675 and AD597 for thermocouple reading". \$\endgroup\$ Commented Feb 10, 2011 at 17:35

2 Answers 2

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Both of those chips are just doing amplification of the thermocouple voltage. They have some features like temperature compensation, open lead detection, and filtering, but not a whole lot more. They're expensive because they're not commonly required, not because their function is difficult.

You could get reasonable results with a single rail-to-rail amplifier. Using the non-inverting configuration:

Wikipedia image

(where Vout ~= Vin(1+R2/R1)), select a large value for R2 and a small value for R1 to get the low-voltage signal into a range that can be read by your microcontroller's ADC pins.

Temperature compensation can be implemented in software, open lead detection can be achieved by a very high value pullup or pulldown resistor (which will cause the amplifier to saturate on one of the rails), but filtering will require some of that analog work you didn't want to do.

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You might want to look into:

  • MAX31850/55/56

    • 1-wire version can be quite cheap ($3-5 in single quantities)

    • SPI can bankrupt you with 4-5$ range

  • MCP9600

    • if you need I2C, at pricey $5

It may help with the thermal sensing endeavours. Generally, searching Digikey for "thermocouple" an sorting by price can be enlightening.

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    \$\begingroup\$ I actually ended up copying this reference design and doing the polynomial maths and CJC in software: microchip.com/DevelopmentTools/… The MCP3421 costs less than $2 \$\endgroup\$
    – Tim
    Commented May 4, 2018 at 8:04

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