Control Interfaces
When the Singularity comes, you’ll program your
home with pure consciousness. Until then, you’ll need
to tell any home automation system how to behave.
Even in a smart home where actions auto-trigger
based on occupancy sensors or weather patterns,
you need some sort of setup screen or programming
interface to define your system’s behavior. Some of
the latest commercial graphical interfaces can provide a terrific front-end to custom hardware projects.
Protocols
Communications protocols dictate how well the
automated devices in your home talk; they can mean
the difference between a sprinkler system that turns
off at the right time and one that floods the driveway.
Some protocols send signals over electrical wires,
others send them over the air. They all vary according
to reliability, hackability, and security. The best opportunities are with protocols whose licensing bodies
offer affordable developer kits for people who want
to experiment.
Physical Interfaces
Getting signals to zip around your home is one thing.
The real challenge is ensuring that they trigger the intended actions. At the edge of the network, proximity,
temperature, infrared (page 118), and other sensors
provide inputs to the controller. And for outputs,
devices need to translate commands into steps, such
as turning on a 240-volt power supply or operating a
window-blind servomotor, then report back on device
status to confirm success of the mission. (All protocols except X10 have a feedback system built-in.)
42 Make: makezine.com/30
Cloud Service With a “cloud” inter-
face, changes made on any web-con-
nected device are routed back through
the network to your home. Having
the magic happen on a distant server
means always-on status, cross-platform
compatibility, and mobile access.
Setting up these services — such as
Digi’s iDigi Device Cloud, Verizon’s
Home Monitoring and Control, Lowe’s
Iris Smart Home System, or Xfinity’s
Home Security — entails paying a fee,
installing a home internet gateway, and
logging into the company’s web page.
ZigBee This protocol is based on the
IEEE 802.15.4 standard for general-purpose wireless, plus some additions
owned by the ZigBee Alliance (zigbee.
org). It works on both 915MHz and the
more common 2.4GHz frequency, with
a range of 50 meters. Dumb nodes like
sensors and switches sleep a lot, so
they can run for over a year on battery
power, while the rest of the system does
the heavy lifting of routing the 250kbps
data stream. This means you need to
install at least one “coordinator” ZigBee
node in a network (page 66). If you want
to create the next ZigBee must-have,
developer kits cost $150–$300.
Z-Wave This fast-growing standard
( z-wavealliance.org) sends radio signals over the air on the 908.42MHz
frequency, sometimes running afoul
of cordless phones, but avoiding the
increasingly crowded 2.4GHz space.
Plug-In Switches The simplest
modules plug in to wall power and
control any device that you plug into
them. All protocols have such wall warts
(prices vary from $10 to $200) as well
as receptacles you can install in-wall for
a seamless appearance. You can also
control an outlet from a microcontroller
using the PowerSwitch Tail II, which
simply takes a digital pin output
(3–12V DC, 3mA–30mA) to switch
an integrated 120V AC, 15A plug.
Built-In Control Devices All
home automation protocols feature
