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Basic Electronics » Using a thermometer with the nerdkits microcontroller.

January 14, 2011
by jingham06
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If I were to purchase a basic thermometer, would I be able to use this to get the data into the microcontroller provided with the nerdkits? I'm mainly looking to broadcast the temperature information but I'm going to tackle that once I've got the data!

January 14, 2011
by Ralphxyz
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You all ready have a basic thermometer in your Nerdkit.

Have you gone through the Nerdkit User Guide yet?

Ralph

January 14, 2011
by jingham06
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Sorry I should have specified! Indeed I did, however I am looking to measure the temperature of a fish tank. I'd just like to guarantee that the thermometer I've bought was made for this and do not know how the chip included with my nerdkit would effect my fishes! If you see what I mean...

January 14, 2011
by Ralphxyz
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Well the chip would not be immersed in the fish tank it would have to be contained in a water proof sleeve or container. You could possible use a piece of heat shrink tubing as long as you seal the end. That would isolate the tempsensor from the fishes. So the LM34 should work fine.

What thermometer are you looking at?

Does the thermometer have a output port or are you going to take a digital thermometer apart and try to grab the output?

Ralph

January 14, 2011
by jingham06
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Will the thermometer pose any threat to the fish in the tank? I've bought a cheap aquarium thermometer: http://www.amazon.co.uk/gp/product/B001EH5O5Y/ref=oss_product I was hoping that there would be a similar chip inside (im not sure if this stuff is standard). It's more the temperature reading part from this thermometer that I'm after.

January 14, 2011
by Rick_S
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I've often found resistive thermisters in devices like that. They are a lot cheaper than the ic's in the kit and make a lot of sense from a manufacturing perspective. It's really hard to say though. You may or may not be able to easily adapt that to the kit.

Rick

January 14, 2011
by Ralphxyz
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If you put the Nerdkit LM34 temperature sensor in a heat shrink tube the fish will only be exposed to the plastic tubing. You might need to order the heat shrink tubing on line to get a long (36" x 3/8") piece. You can use a piece of cork to plug one end and use a soldering iron (a hot air gun is better) to shrink the tube around the cork. You would only have to shrink the tube at the end not the whole tube. You could put the LM34 with extended wires attached in the tube and then fill the tube up with sand so that it would not float or you could let it float.

Or you could get some 3/8" copper tube and solder and crimp the end closed.

Chances are you would destroy the case of any store bought thermometer or at least ruin its water tightness by trying to get to it's temperature probe.

This will be fun wish I had some fish.

Ralph

January 15, 2011
by Rick_S
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Ralph, I don't know if you looked at his thermometer or not, but what he linked to has a temp probe on a long wire with suction cups attached designed for underwater use.

jingham06, Chances are the temperature probe on that device will have two wires. A thermistor simply acts as a variable resistor that varies by temperature. I believe some are logrithmic and some are linear but I may be wrong on that one. Finding out how much the resistance changes per degree, doing the math to determine what that would mean in voltage drop, then reading that with the micro should be feasable.

It would take some experimentation though to find out the change per degree and if it's linear or logrithmic. Once that was established the rest would just be building a circuit around it and doing the math to translate it's output into something you want to see.

Take it apart and post some photo's of the board up close where the probe wires attach and of the surrounding circuitry. That will give a better idea of what you have.

Rick

January 15, 2011
by jingham06
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Hi thanks for the replies! I'll wait until it arrives and dismantle it. And you are right, the one I've ordered has a couple of wires with a waterproof end with suction cup going into the unit.

I will keep you posted with the project and how it goes. I've got some of my code sorted (just using the thermometer that came with the nerd kit for now). This feeds into a python script which tweets the temperature and time. I can then pick this up from a thin client such as iPhone/Android. I'm also using a product called Splunk to monitor the RSS twitter feed so I can have an alarm set off when the temperature gets too low :)

Thanks again.

January 15, 2011
by Hexorg
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Hey, well I looked at the thermometer, and it has digital output, so inside there must be at least one chip to measure the data from the thermometer and output it to the screen. Also, there is a high chance of having one chip measure data, send it to another chip that'd output it to the screen. In first case you could probably replace the screen with the nerdkit's microcontroller, and in second case it'd be even easier - just connect nerdkit chip instead of the second chip, and interface it similar as in digital calipers tutorial.

January 15, 2011
by Ralphxyz
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I had missed the link for the thermometer. Yup, you should be able to use the temperature probe once you figure out it's output.

Ralph

January 25, 2011
by jingham06
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I've got the thermometer now. What's the best way to approach this? Should I use the thermometer with the thermometer chip I got with my nerd kit or without it?

January 25, 2011
by Rick_S
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First step would be to open it up and look inside to see what's in there... Post photo's

:D

RIck

January 25, 2011
by jingham06
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Well I removed the thermometer from the board of it, but it's pretty cheap and I can't really see much. Will upload a photo in a sec...

January 25, 2011
by Rick_S
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I don't know if I would have removed it... I was more speaking of taking the case apart so we could see how the temperature probe attached to the board and if there were any identifiable ic's on the board. Often inexpensive devices will just have an epoxy blob IC that can't be recognized easily.

January 25, 2011
by jingham06
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http://ing0.co.uk/pics/temp.jpg

This is what I've got. The wires go off to the thermometer, and as far as I can tell there isn't a controller in that (it's also the part which is submerged in the water).

January 25, 2011
by Ralphxyz
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Do you have a multi meter to get some readings on the probe wires? You should not even need to remove them from the PCB.

Ralph

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