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### Topic: Multiplexing a Thermocouple Input (Read 14514 times)previous topic - next topic

#### synfinatic

#30
##### Feb 27, 2011, 05:42 pm
FWIW, as promised, I was able to calculate the S/H coefficients for the Thermoworks probes.  I haven't done extensive testing, but seems to be accurate to a few degrees F using a 10K resistor divider.  I haven't yet calculated if that's the most optimal value yet, but it seems to provide a reasonable starting point.  I created a new threads so hopefully it's easier for others to find in the future.

http://arduino.cc/forum/index.php/topic,53675.0.html

#### Drunk_J

#31
##### Mar 14, 2011, 08:34 amLast Edit: Mar 14, 2011, 10:19 am by Drunk_J Reason: 1
I'm a little late on the conversation, but was wondering if you had seen this project (link below).  Anyway, thought it may help.

http://hruska.us/tempmon/

Or this if you're still looking at thermocouples.
http://www.mlgp-llc.com/arduino/public/arduino-pcb.html

Thermocouple source (type K) - http://www.thebbqguru.com/products/Meat-Probe-%28DigiQ%2C-CyberQ%29.html

-=J

#### synfinatic

#32
##### Mar 15, 2011, 01:55 am
Wasn't aware of those projects, thanks for the links!  Looks like quite a few people have tried to create various smoker datalogger & controller solutions. One thing that other's may be interested in are the S/H coefficents for the Maverick thermistors which I found at the very bottom of this page: http://hruska.us/tempmon/BBQ_Controller.pde

A = 2.3067434E-4
B = 2.3696596E-4;
C = 1.2636414E-7;

The author is using a 22.2K resistor as a voltage divider.

I haven't verified how good these numbers are, but sounds like a lot of people have Maverick probes already and may find those numbers useful.

#### Drunk_J

#33
##### Mar 15, 2011, 08:29 am
No problem.  BTW, I just ordered the TC4 shield and LCD board from the thermocouple link I listed above.  I already have numerous thermocouples from BBQ Guru folks (they are plenty accurate), so decided to take that approach.  Though I will have to change the term blocks on shield to jacks to match probes (prefer plug in option).  They also have a software project site for their shields - http://code.google.com/p/tc4-shield/ .  The shield was developed for coffee roasters.  Hoping it will not be a far stretch to adapt to a smoker.

-=J

#### BigJohnT

#34
##### Mar 15, 2011, 01:02 pm
Synfinatic,

Thanks for the S/H coefficients. I'm still working on the MAX6675 ADG609N combination as time allows. I've almost got it wired up and ready to test. When I get done with that I'll test the Maverick thermocouples again. They would be more cost effective than the thermocouples and simpler to wire up.

John

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