This week, I began work on the body temperature sensor. Since putting the sensor in the user’s mouth would be an annoyance and present a possible choking hazard when performing physical activities, we decided to aim for locating the sensor under the user’s armpit.
We decided, at least for the first release, to go with the TMP102 temperature sensor breakout board from Sparkfun Electronics (http://www.sparkfun.com/products/9418). Its small size will allow us to place it at the measurement location and send digital readings back to the Arduino over standard wire. A thermocouple based unit would be more stiff and inclined to break over prolonged use or if kinks developed in the thermocouple wire. Also, it would, probably, require a separate reference junction for accurate measurements. As an added bonus, Sparkfun provides pre-written Arduino code for this unit which can be found hosted on the Wiring website here: http://wiring.org.co/learning/libraries/tmp102sparkfun.html.
Below, you can see a picture of my test setup wiring connecting the temperature sensor to the Arduino Mega 2560 I’m using for prototyping purposes. I’ve included an American penny to give some reference for the size of the unit. For this unit, we’ve soldered pins to the terminals so that it’s easy to breadboard. The final version will need to be soldered directly to some high-durability shielded wire and installed into some kind of housing with a wire strain relief to ensure a longer life under, potentially, abusive conditions.
In the second photo, you can see the sketch being run on the Arduino Mega. As you can see, the serial interface shows the temperature values being transmitted, in degrees Celsius, from the unit every half a second.
That's it for now. Next time, I'll delve into fabrication of the finished, ruggedized, probe.