■ FIGURE 7.
Protecting the Sensors
Although the Dallas sensors are small and fairly
rugged, they should be protected from physical damage
with some kind of a guard or by careful placement on
The sensors on my compost monitor are exposed to
sticks and the sharp end of the shovel when it's being
installed in a pile. That is okay on a prototype (Figure 7),
but will need to be addressed before production is started
on the real thing. A smooth little plastic cover or spot of
epoxy will probably do the trick.
Lastly, make sure you don't exceed the temperature
range of the device. Don't put a sensor in direct contact
with a glowing heating element if you just want to
measure the temperature in an enclosed space.
Otherwise, the device will likely be destroyed.
We've seen that the Dallas DS18B20 sensors are easy
to use with the Arduinos. Although a little more expensive
than using a thermistor, the DS18B20s are very accurate
and accommodate multiple sensors on a single input pin.
This arrangement can satisfy a wide range of temperature
You might also explore some of the other Dallas one-wire devices. They include memory modules, clocks, a
digital potentiometer, and more. Now that you have
exposure to this data input methodology, maybe some of
the other types of devices will satisfy your design needs.
Give the Dallas sensor a try. No doubt, you'll start
dreaming up some really interesting applications. NV
Rob Reilly is a technology consultant, writer, and
portable computing expert. Early adopter tech trends,
seminars, and media projects are his stock-in-trade. Links
to many of his published articles appear on his website at
http://home.earthlink.net/~robreilly. Contact Rob at