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.
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I've had good luck using this chip, particularly when I compare it to the AD595-AQ.
What I like:
What I don't like:
ADC timing gotchas, :
I've used this successfully in a project which uses:
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!
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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
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?
update: It works...
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.