Thermocouple Amplifier Digital MAX6675

MAXIM IC MAX6675 Cold Junction Compensated K-Type Thermocouple to Digital Converter. This simple 8-pin SOIC IC attaches directly to any K-Type Thermocouple and interfaces via a SPI read-only interface.

Works great with 8-pin SOIC to DIP adapters.

  • 0.25C Resolution
  • 0C to +1024C
  • Minimal 2-wire digital interface

Thermocouple Amplifier Digital MAX6675 Product Help and Resources

Core Skill: Soldering

This skill defines how difficult the soldering is on a particular product. It might be a couple simple solder joints, or require special reflow tools.

3 Soldering

Skill Level: Competent - You will encounter surface mount components and basic SMD soldering techniques are required.
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Core Skill: Programming

If a board needs code or communicates somehow, you're going to need to know how to program or interface with it. The programming skill is all about communication and code.

3 Programming

Skill Level: Competent - The toolchain for programming is a bit more complex and will examples may not be explicitly provided for you. You will be required to have a fundamental knowledge of programming and be required to provide your own code. You may need to modify existing libraries or code to work with your specific hardware. Sensor and hardware interfaces will be SPI or I2C.
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Core Skill: Electrical Prototyping

If it requires power, you need to know how much, what all the pins do, and how to hook it up. You may need to reference datasheets, schematics, and know the ins and outs of electronics.

3 Electrical Prototyping

Skill Level: Competent - You will be required to reference a datasheet or schematic to know how to use a component. Your knowledge of a datasheet will only require basic features like power requirements, pinouts, or communications type. Also, you may need a power supply that?s greater than 12V or more than 1A worth of current.
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Customer Comments

  • Gnnh. I needed one that goes past 1700C for accurate temp measurement for melting titanium.

  • This is a great chip for thermocouple applications. I had used this years ago for a project. I had documented my work with it, which some may find helpful. Check it out here: http://www.nuclearprojects.com/thermocouple/

  • I was really interested in the tutorial link, but it is broken!

    I found another one here, in case Michael’s tutorial is permanently gone: http://learn.adafruit.com/thermocouple/overview

  • So….Is there any reason we couldn’t use an E-type thermocouple, and use the reported Celsius value to backcalculate the real Celsius value?

    Maybe I don’t follow exactly what’s going on.

  • would this work with Serial Multiplexer Breakout - TS3A5017
    (sku: BOB-08970)
    Has anyone tried this? I would like to use 4 thermocouple probes, but avoid expense of 4 of MAX6675 chips.
    Is there a BOB board available for this chip?

    • In theory I think may affect the cold junction compensation a little, as would having long tracks between where the thermocouple terminates, and where the IC is located (as it measures temp on the IC to compensate)
      I see no reason why it would cause a problem,
      in particular the amplifier is likely Hi-z, and the source impedance of the thermocouple is low, like 1R ~ 10R depending on the particulars.
      offsets introduced by using the switch (if there are any) would be the thing to look out for.

  • Has anyone tried using these on a shared SPI bus?

  • There’s a nice Arduino Max6675 Library available to really simplify reading temperature data from this amplifier.

  • Could I use a multiplexer with one 6675 to read from multiple thermocouples, or do I need a 6675 for each thermocouple in my project?

    • No, Use separate chips and use common ck and DO lines and then have multiple CS lines. Works great for me.

Customer Reviews

2.5 out of 5

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2 of 2 found this helpful:

Handy little chip

I’ve had good luck using this chip, particularly when I compare it to the AD595-AQ.

What I like:

  • Handles amplification and ADC on the same chip. I don’t need to worry about analog signal routing, or any of the complications of ADC accuracy on the µC.
  • Really simple pinout, therefore a simple board layout.

What I don’t like:

  • The MAX6675 Arduino library isn’t suitable for state-machine-based µC applications. I needed to write my own low-level SPI routines due to both timing and SPI compatibility issues.

ADC timing gotchas, :

  • Be aware that since the ADC conversion starts upon taking CS high, it might be wildly out-of-date if, say, you’re only reading the MAX6675 every minute or so. Toggling CS low, then high can get around this.
  • If you take CS low during a conversion, it’ll stop the conversion that’s already in progress. I seem to recall it’ll just return the previous value in this case. So, don’t read faster than about 4Hz.

I’ve used this successfully in a project which uses:

  • 5V supply
  • ATMEGA328P-AU Microcontroller
  • Other SPI peripherals on the same bus
  • Maximum 4Hz read rate

Worked for a while...then self-destructed!

Not sure if I just got a bad part or if there’s a larger quality issue here, but I attempted to use one of these devices in an oven control with a standard type K thermocouple. Power was 3.3V.

The device worked perfectly for several hours including multiple power cycles for testing purposes. After those few hours (fortunately during a test cool-down cycle) suddenly the temperature readings went to zero, and on subsequent power cycle the chip literally exploded (!) destroying the attached ARM controller circuitry in the process (probably due to shorting out and applying either 0V or 3.3V at high current to the delicate SPI pins). I have no idea how this is possible besides a manufacturing defect; the 3.3V supply was rock stable throughout and the ARM device on the same supply didn’t blink until this chip exploded.

I have been in electrical engineering/embedded systems for well over a decade so I know all about ESD precautions, etc. This is the first time I have had a non-Chinese sensor chip do anything like this!