Raspberry Pi Hacks

Chapter 4. Hacking the Outdoors

Electronics outside, you say? Isn’t that a bad idea? We do have a couple of water-resistant suggestions ([Hack #39] and [Hack #40]). But we also have ideas for how to put your Pi to use on your outdoor projects, from monitoring your garden ([Hack #38]) to controlling your holiday lights ([Hack #45]).

Hack 37. Tell the Temperature Outside (Without Going Out There)

The outside temperature is not a constant value; it fluctuates, and we know you like to know what it is. Whether you’re helping plants stay healthy or just want to know how many layers of clothes to wear, this hack can help!

[Hack #5] shows that the Raspberry Pi measures the temperature of its BCM2835 system-on-chip, but this is different. In order to read the temperature near the Raspberry Pi (or even nowhere near it), you’ll need to connect a temperature sensor. While Linux supports some USB thermometers, it is just as simple (and arguably more fun), to wire up a simple temperature sensor to the GPIO on the Raspberry Pi.

This hack uses the Texas Instruments TMP102 I2C temperature sensor for the following reasons:

• It is very small. Smaller than a quarter. See Figure 4-1 for proof.
• It is a digital sensor (this makes the wiring much easier and the results much more accurate).
• Sparkfun sells it already connected to a breakout board.
• It is cheap (less than $6 USD at the time of this writing).
• It is accurate over a range of temperatures from -25°C and +85°C. (That’s -13° to 185°F.)

Figure 4-1. TMP102 ...