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Home Automation Project - May 2011
There is a lot of old technology out in the Home Automation industry, a lot of technologies have come and gone, and only a number of reliable standards remain. First you need to get up to speed with some basic terminology.
Standards that are here to stay:
| RS485 |
Twisted pair 2 wire multi-point (i.e multi-drop daisy chain your switches or devices on the wired network) this entire length of wire multi-drops is called a 'Bus'. normally each device has two plugs, one for in, one for out, or you twist the wires together and screw into the same screw location. At each end of the 'Bus' you need to put terminators (a little resistor or plug) this stops the signals reflecting off the ends of the cables and coming back down the bus. Twisted pair is immume to noise and interferrence, makes it ideal for a 'Bus' up to 1000metres long.
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| Ethernet |
Twisted pairs Cat5 or Cat5e(shielded) or cat6 cable for Network cabling, used for sending HDMI high def also sometimes, can also send low power voltages down the wires to power devices this is called PoE (Power Over ethernet, the connectors at each end are called RJ45. All modern desktop and mini PCs have one of these plugs. |
| Z-Wave |
Wireless broadcast commands only to those that are programmed to listen, each device is addressable, therefore provides smart network of routable wireless devices. There are 3 frequency models depending on your part of the world. |
| USB |
PCs, Laptops and mini laptops, and standalone Android devices all still have usb interfaces, it is the most common interface in the world. It allows for cheap USB multi port hubs and fast plug and play recognition. USB passthough is 1 millisecond, so it is very fast too.
You can get USB to Infrared, USB to RS232, USB to RS485, USB to Z-Wave, USB to Ethernet, USB to X10
Because of all the available USB adapters, this makes the ideal and cheapest solution for a central controller.
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| Infrared |
These come in two styles: Transmitter (i.e remote) and Receiver i.e TV, Satellite or Cable box, AV (audio visual) equipment. |
| RS232 |
Most people recognise this as a 'com port' yes it is the same thing. This is used to send data and commands down a single straight wire pair (non twisted) these short lengths are useful for connecting AV equipment together so that they can communicate without the need of infrared adapters. RS232 can be easily prone to noise and interferance when used in long lengths of wire. |
| WiFi |
Otherwise know as wireless b/g/n. N being the fastest. also known as 2.4Ghz wireless. also used in all laptops for wireless networking back to your ADSL internet router. Wireless N can be speeds up to 300Mbps. Definately get a Wireless-N ADSL network router for your house. |
Depreciating Standards:
UPB (old PowerLine technology)
C-Bus (RS485 two wire multi-point, 35V power is also on the same wires as the signal)
X10 (retrofitting houses will use this to get signals down the power lines when the AC signal crosses the 0volts mark, inherintly unreliable as pressing two buttons at the same time will conflict)
Zigbee (broadcast shortrange signals, within the house, broadcast storms means the same command gets broadcasted by each zigbee device leading to slow response times)
802.15.4 wireless
(aka 6lowNet, Zwave, Zigbee) is getting more interesting as more chip makers start up the manufacturing processes...
http://www.automatedbuildings.com/news/oct10/articles/sinopoli/100928010404sinopoli.htm
http://www.cel.com/pdf/press/zigbee_helps_light_future.pdf
Differential signals with RS485: (source: lammertbies)
Longer distances and higher bit rates
One of the main problems with RS232 is the lack of immunity for noise on the signal lines. The transmitter and receiver compare the voltages of the data- and handshake lines with one common zero line. Shifts in the ground level can have disastrous effects. Therefore the trigger level of the RS232 interface is set relatively high at ±3 Volt. Noise is easily picked up and limits both the maximum distance and communication speed. With RS485 on the contrary there is no such thing as a common zero as a signal reference. Several volts difference in the ground level of the RS485 transmitter and receiver does not cause any problems. The RS485 signals are floating and each signal is transmitted over a Sig+ line and a Sig- line. The RS485 receiver compares the voltage difference between both lines, instead of the absolute voltage level on a signal line. This works well and prevents the existence of ground loops, a common source of communication problems. The best results are achieved if the Sig+ and Sig- lines are twisted. The image below explains why.
Noise in straight and twisted pair cables
In the picture above, noise is generated by magnetic fields from the environment. The picture shows the magnetic field lines and the noise current in the RS485 data lines that is the result of that magnetic field. In the straight cable, all noise current is flowing in the same direction, practically generating a looping current just like in an ordinary transformer. When the cable is twisted, we see that in some parts of the signal lines the direction of the noise current is the oposite from the current in other parts of the cable. Because of this, the resulting noise current is many factors lower than with an ordinary straight cable. Shielding—which is a common method to prevent noise in RS232 lines—tries to keep hostile magnetic fields away from the signal lines. Twisted pairs in RS485 communication however adds immunity which is a much better way to fight noise. The magnetic fields are allowed to pass, but do no harm. If high noise immunity is needed, often a combination of twisting and shielding is used as for example in STP, shielded twisted pair and FTP, foiled twisted pair networking cables. Differential signals and twisting allows RS485 to communicate over much longer communication distances than achievable with RS232. With RS485 communication distances of 1200 m are possible.
Differential signal lines also allow higher bit rates than possible with non-differential connections. Therefore RS485 can overcome the practical communication speed limit of RS232. Currently RS485 drivers are produced that can achieve a bit rate of 35 mbps.
Lighting Systems: what you need:
You need some microcontrolled switches, some microcontrolled relays and microcontrolled dimmers (they go near the circuit breaker panel) , some low voltage (12v/24v/35v) power modules to power the microcontrollers inside the switches and leds, in the switches, and to give a little bit of power for switching the relays and dimmers on/off. You need the TPS Electrical wire (125v-240v AC) to go from the light fittings back to the computer controlled relays/dimmers. You will also need some RS485 (see above for defn) wire for multi-drop chaining the switches.
What does a micrcontrolled dimmer look like:
What do microcontrolled switches look like:
$230NZD and $235NZD
Vantage Infusion Controller $2265NZD
Wiser
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