Yuri_Rage

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kladue

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Thank you Yuri, that looks like the right one

JeepGuy

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Looks good Yuri. Now for the dumb question of the day. If I get something like that put together, what do I need to get a read out from it? I guess I mean...could I simply rig up a plug to fit any digital thermometer unit and get accurate results?

Clearly, when it comes to some stuff like this, I'm out of my league a bit, but I like the idea and might try it if I can figure out how to make it work for me.

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Yuri_Rage

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I was waiting for this question. You can't necessarily just connect any old sensor to any old digital thermometer - you have to know what kind of sensor was used in the first place (and there are lots of kinds). However, I do have a two answers for you, one simple, and one rather complex.

First, the simple answer:
If you have a digital thermometer that doesn't have a submersible probe, you can just encase the probe in some epoxy and stainless tube. That's what I was getting at with the "anyone can do this project" comment.

Now, the complex answer:
If you want to make a new probe for an old thermometer, some reverse engineering is in order. You can probably determine if a thermistor is the sensor of choice, because there will probably only be two wires on the probe output. Connect a multimeter and read the resistance value across those wires at several temperatures. That should give you an idea of the type of thermistor inside it. Here's a page from the Jameco catalog that may help (as you can see, thermistors are cheap!).



If you've got three or more wires coming from the probe, it's probably a digital sensor like the LM34 that I used. Trying to reverse engineer one of those will likely fry it if you connect it backwards or apply too much voltage. In general, they operate at about 5VDC, red=positive, black=negative, green=ground, and other wire colors are likely to be sensor output. The sensor output will be something less than the input voltage. Jameco sells LM34 sensors for less than $5.00 a piece. I use the probe I made to feed my computer digital temperature information via an Arduino microcontroller (in short, I made my computer into a big digital thermometer).

Does that help?

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JeepGuy

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Actually it does. Thanks.

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brewman !

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LM34s put out 10mV per degree F and can be powered by 5V. So if you have a digital multimeter around that reads mV, that would work pretty well. You would have to hook up a battery to power the sensor. You might be able to use the battery in the multimeter.

70F would output 700mV or 0.7V
150F would output 1500 mV or 1.5V.

www.digikey.com Search on LM34. Follow the links to the datasheet.

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Fermenting: Red Herring Lager with wrong ingredients.
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Consumed Brown Ale (Newcastle clone), Blue Moon (Belgian Wit) Thread, Cranberry ale, Corona clone.


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seyahmit

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I just got the Ranco controller. I don't have the probe in front of me and want to drop by the hobby store to get some stainless tubing. What inside diameter tubing should I get?

Tim

Yuri_Rage

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The stock Ranco probe is 1/4" in diameter. 1/4" ID tubing might work with a tight fit, but you'd want to take the probe with you just to make sure.

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seyahmit

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Thanks Yuri! I will pick up 1/4 and the next size up. The probe is currently keeping my beer from freezing.

RoosterCogburn

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bumping old thread for worthy cause,

wiring up my lm34's is producing varying results.
taping together all 3 leads results in a voltage varying enough to fluctuate Farenheit temps about 10-15 degrees.

when I have all 3 leads loose, temps are spot on.
leads length doesn't seem to be a factor, just proximity to each other.
I've tried different styles of leads too, even cat 5 to try and cancel out crosstalk.

any suggestions?
I really don't want 12 feet of flying leads from microcontroller to temp probes