Do you need realtime data or just logging? If you're just logging, and have $40 to spend on a solution, look at the DalSemi^WMaxim thermochron iButton: <a href="http://www.maxim-ic.com/products/ibutton/ibuttons/thermochron.cfm">http://www.maxim-ic.com/products/ibutton/ibuttons/thermochron.cfm</a><div>
<br></div><div>m.<br><br><div class="gmail_quote">On Sat, Apr 10, 2010 at 11:34 PM, Lee Sonko <span dir="ltr"><<a href="mailto:leelist@lee.org">leelist@lee.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="im">> This is excellent. Thank you for the help. I don't mind<br>
> recharging batteries often - but will they operate properly<br>
> for a day, explode, cause aliens to visit my home, or<br>
> anything else weird?<br>
<br>
</div>The batteries won't explode or anything dreadful. I'm pretty sure they'll<br>
deliver a low voltage and wear out quickly. I'll hazard a wild guess and say<br>
you'll get 60% of what would be a full charge out of them. You could<br>
compensate by using more batteries in series and recharging more often.<br>
<br>
You want a very stable voltage source for the thermister's voltage divider<br>
so you should go through the onboard regulator and be sure to have more than<br>
6.0 volts of batteries.<br>
<br>
The Arduino draws about 40ma.. maybe another 10ma for the thermistor. It<br>
would normally run for about 20 days on 1,000ma of batteries. Maybe you'll<br>
get 12 days of battery at low temperature.<br>
<br>
I found this datasheet<br>
<a href="http://www.panasonic.com/industrial/includes/pdf/Panasonic_NiMH_Overview.pdf" target="_blank">http://www.panasonic.com/industrial/includes/pdf/Panasonic_NiMH_Overview.pdf</a><br>
page 10 shows the batteries having low voltage (maybe 0.1 volts low) and 80%<br>
of normal temperature capacity at -10 degrees celcius. That's a good sign<br>
for you I think :-)<br>
<div><div></div><div class="h5"><br>
<br>
<br>
<br>
<br>
<br>
><br>
> I don't mind experimenting, but if I get battery acid in<br>
> the freezer, I'll be in Trouble! (with a capital T). I<br>
> already have petri dishes of genetically engineered e. coli<br>
> in the refrigerator, and am about to put small frozen viles<br>
> in the freezer... oi! :)<br>
><br>
> Glen<br>
><br>
> On Apr 10, 2010, at 8:54 PM, "Lee Sonko" <<a href="mailto:leelist@lee.org">leelist@lee.org</a>> wrote:<br>
><br>
> > A thermister is probably what you want.<br>
> ><br>
> > maybe Jameco product 207037<br>
> > <a href="http://tinyurl.com/ydgvzgo" target="_blank">http://tinyurl.com/ydgvzgo</a><br>
> ><br>
> > The resistance changes according to a curve so it needs to<br>
> be massaged<br>
> > a little. This should do it for you.<br>
> > <a href="http://www.arduino.cc/playground/ComponentLib/Thermistor2" target="_blank">http://www.arduino.cc/playground/ComponentLib/Thermistor2</a><br>
> ><br>
> > If I remember correctly, it's accurate to about +-0.2 degrees.<br>
> ><br>
> ><br>
> > For the batteries at subzero temperatures... ugh. Buy extra<br>
> batteries?<br>
> > This cheap charger works great:<br>
> ><br>
> <a href="http://lee.org/blog/2008/07/10/vanson-8-aa-nicad-nimh-battery-charger/" target="_blank">http://lee.org/blog/2008/07/10/vanson-8-aa-nicad-nimh-battery-charger/</a><br>
> ><br>
> ><br>
> ><br>
> ><br>
> ><br>
> ><br>
> >> -----Original Message-----<br>
> >> From: <a href="mailto:noisebridge-discuss-bounces@lists.noisebridge.net">noisebridge-discuss-bounces@lists.noisebridge.net</a><br>
> >> [mailto:<a href="mailto:noisebridge-discuss-bounces@lists.noisebridge.net">noisebridge-discuss-bounces@lists.noisebridge.net</a>]<br>
> On Behalf<br>
> >> Of Glen Jarvis<br>
> >> Sent: Saturday, April 10, 2010 7:40 PM<br>
> >> To: Noisebridge Discussion List<br>
> >> Subject: [Noisebridge-discuss] Termperature sensor datalogger<br>
> >><br>
> >> I am doing a diy bio experiment on survival rate of e. Coli after<br>
> >> freezing (with different cryo agents). I'd like to make a quick<br>
> >> arduino data logger.<br>
> >><br>
> >> I need to measure temperatures around -20 degrees C (about<br>
> -4 degrees<br>
> >> F.)<br>
> >><br>
> >> I did something like this with my Lego mindstoms sometime<br>
> back - but<br>
> >> it was for a very short amount of time.<br>
> >><br>
> >> I need to take regular measurements (like once every 15 min) for a<br>
> >> month.<br>
> >><br>
> >> Does anyone know a good vendor for a temperature sensor in this<br>
> >> range?<br>
> >> What are the issues I may encounter operating a battery in<br>
> sub zero<br>
> >> freezing temperatures on an ongoing basis? I don't mind<br>
> changing out<br>
> >> batteries or retrieving device for data retrieval once per day.<br>
> >><br>
> >><br>
> >> Glen<br>
> >> _______________________________________________<br>
> >> Noisebridge-discuss mailing list<br>
> >> <a href="mailto:Noisebridge-discuss@lists.noisebridge.net">Noisebridge-discuss@lists.noisebridge.net</a><br>
> >> <a href="https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss" target="_blank">https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss</a><br>
> ><br>
<br>
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</div></div></blockquote></div><br></div>