Hardware Reference
In-Depth Information
cated by the range of temperatures it experiences, and each zone is given an
identifier code. For example, Tom's plant hardiness zone is 5b, and Ruth's is 7a.
See
http://planthardiness.ars.usda.gov
for a map of all the U.S. zones (and to
discover your zone). Also, some plants tolerate frost and freezing better than
others, so depending on your plants, temperatures dropping below 0°C could
result in plant death.
Measuring the space, soil, and air is not simple to do, but we can measure the amount
of water in the air and the temperature of the garden. You can also measure the in-
tensity of light near the plants using the light sensor in
Hack #42
, but this hack will
focus on monitoring temperature and water (humidity).
Serious Gardeners
If you're a hardcore gardener, you might point out that while humidity is interesting,
it is less interesting than rainfall measurement (assuming your garden is not in a
water-controlled greenhouse). To get that, you need to wire up a rain gauge sensor.
There are several different rain gauge sensors on the market, but connecting them
to a Raspberry Pi and getting the data is a bit more complicated. There are some
1-Wire rain gauge units, but the Raspberry Pi does not have a 1-Wire connector. You
can get around that by building a circuit to connect it to GPIO (either via the w1-
gpio driver or the I2C bus), or you can buy a 1-Wire-to-USB converter (like the
Maxim Integrated DS9490R#).
From a software side, you can use
OWFS
to read the data from the 1-Wire device.
This can get complicated quickly, so we'll leave this as an exercise for the motivated
and serious gardener. For the rest of us, we'll start with humidity and work our way
up.
While it is technically true that your plants are growing in real time, they are doing it
so slowly that you have to watch them over long periods of time to see the growth.
(Search YouTube for “time lapse of plants”; it is rather freaky and cool.) As a result,
we do not need to have real-time measurements of temperature and humidity, so
using a sensor like a TMP102 (as in
Hack #37
) is overkill. Instead, we can use an “all-
in-one” temperature and humidity sensor. Adafruit has an excellent one from Adsong,
the
AM2302
.
Here are the main reasons the AM2302 sensor is a good one for this hack:
• It is sealed up in a plastic body, which will help it be resistant to Mother Nature's
wrath. It also has a mounting hole, so you can attach it (either by hanging or
screwing) in a secure location in your garden.
• It is a digital sensor, so it is accurate and simple to wire.
• It reads in new data every two seconds, which is nowhere near real time, but is
more than sufficient for monitoring plants in a garden.
