Hardware Reference
In-Depth Information
One such device is the DIN Relay III (from
http://www.digital-loggers.com/din.html
), which is WiFi enabled
and allows you to control up to eight devices, powered by either AC or DC, at once. This has natural benefits of scale
if you have several devices located in a cupboard under the stairs for example. Even if your current house wiring isn't
home run (to a single location) this device makes such a task more tempting, because it provides a centralized control
system with very little expense.
Although it has a scripting language (which is wholly ignorable!) it does have scheduling and a built-in status
LCD that is controllable, and need not display information about the status of the unit.
Low Voltage Control
For many applications having control over a 115/240V power line isn't necessary. This is because virtually all household
devices work on a much lower voltage, usually 24V or less. This includes a number of more modern 24V light bulbs.
Therefore, instead of controling the device at the plug you can bypass it, and switch the current flow between the exit of
the power supply and the entrance to the circuit board.
N
Some devices have dual power lines, such as a 3.3V and a 5V rail. In this case you will need a “double throw”
relay so that both power circuits can be opened, or closed, at the same time.
Note
This switching action can happen with any suitable relay. What determines a “suitable” relay is governed by
the “contact ratings.” This is how much current, at a specific voltage, a relay is capable of safely switching. If this is
exceeded the relay could remain permanently on, or off, without any warning that it is doing so. These are always
specified on the relays, or the switching units that use them. The National Electrical Manufacturers Association, or
NEMA, have introduced a series of designations for both AC and DC, which indicate the type of current flow, and the
maximum voltage.
You can build your WiFi Relay Switch using an Arduino, a relay, and the guidelines above for digital output control
of an Arduino. For those looking for a prebuilt solution,
http://www.relaypros.com/Relay/Relay/Wi-Fi_Relay
, and
http://www.relaycontrollers.com
(along with many others) both provide suitable functionality.
Of course, it needn't be an Arduino controlling the relay as a Raspberry Pi, or any form of Microcontroller, can
handle the task equally well. One famous case of this was “Feed Toby,” by Nat Morris (
http://www.natmorris.co.uk/
feedtoby
) who used a Micrcontroller to release food pellets to his pet dog, via Twitter. In this case a motor was used
instead of a relay.
Conclusion
In the same way that you can build complex and evocative systems using a couple of well-chosen pieces of
hardware, so can you build smart automation tools with a minimum of effort. By using alternate input devices,
such as pressure mats and joysticks, you can change the way that you interface with your home. By adding alternate
output devices, perhaps powered by old game consoles, you supply visuals to areas previously inaccessible to
full-scale desktop PCs. And the introduction of robots and computerized welcome mats adds a level of previously
unknown of coolness to your home.
Search WWH ::
Custom Search