Results of 1 week test run: best system yet!

We just got back from a trip over Thanksgiving during which I left the new monitor running. The latest version measures two temperatures using 10K NTC thermistors, reports them periodically via twitter, and responds to SMS messages it is sent by returning the two temperatures. SMS can be sent via email or cell phone, and will respond in either case via email or SMS depending on where the SMS came from.

Happily the unit performed flawlessly. I got twitter reports as expected and responses to SMS from my iPhone and emails. I had the unit set to tweet every 2 hours, or when the temperature changed more than 5 degrees F.

The unit is much less expensive, simpler, lower power and more reliable than either of my earlier Linux based approaches. The hardware cost is $39 for the SIM900 modem shield and $28.80 for the Arduino, plus $11.99 for the power adapter and $7.99 for the case. I built the 10K NTC temperature sensors my self at negligible cost.

Here's a screenshot of the order from http://store.linksprite.com/:

The SIM card is my old AT&T Gophone account SIM, for which I buy packages of 1000 SMS for $9.99/month. At 30 SMS/day hat is more than enough for experimenting. If I built another for the condo I could probably use the cheaper Arduino pro.

Bottom line is the unit cost total of about $89 for the (unpackaged) hardware and $9.99/month cell service. That's a lot lower monthly cost than a unit that requires an internet connection, at least for moderate data usage packages.

Interestingly, my cell phone SIM from Black Wireless, an AT&T distributor of pay as you go service, worked from the cruise ship, which provided cell service at sea for the same $0.05 per SMS and voice minute (although I did not try to make voice calls.)

Here's a twitter page: