DIY WiFi x.10?

December 4, 2005 11:43 AM

What would be involved with coming up with a wireless (WiFi) solution to remotely control one or several 110v relays over a wireless network? While this is not necessarily the application, think remote control of Christmas lights. I'd prefer to avoid X.10 if possible.

Inexpensive is good, cheap is better.

I have basic electrical skills and can solder up a circuit board, but lack the knowledge and research time (and probably skills) to develop a solution in PIC, etc..

I'm unsure if there is a simple solution because I can't imagine why someone already hasn't come up with it as the potential applications would be many. Kind of like X.10 but IP addressable over a network or even the internet.

posted by Lactoso to Computers & Internet (17 answers total)

The usual solution is to use X10, but then have a computer connected to an X10 controller to send the signals. Having each switch have its own IP address is just stupid; WiFi chipsets are nowhere near as cheap as X10 chipsets.

If it's X10 reliability you're worried about, Insteon is making good headway at replacing it, but it's still in early stages of rollout. The switches are there, but computer control is just now becoming available. (If you're on a Mac, have a look at Indigo.)

Zigbee is like X10 and Insteon but wireless, but it's even less available.

There may be a problem with all of these if you are looking to spam commands constantly; they're more designed for home automation tasks, not flashing lights on a constant basis. If that's what you're trying to do, hardwired is the path that's usually taken, sorry.

Basically, the common requirements are satisfied by existing products, and your requirements are uncommon enough that it isn't cost-effective to mass-produce.
posted by trevyn at 11:54 AM on December 4, 2005

The problem with X10 is speed, because it only sends a few bits on each zero crossing of a 60 HZ signal, if you have a lot of things to control it can take multiple seconds to address them all together.

The real time effect of dimming the currently selected light is a trick and only works for the currently selected light.

To control numerous, say 256, lights together is not practical in real time, because a large header must be sent to select the current unit.
posted by StickyCarpet at 1:13 PM on December 4, 2005

Forgot to mention, Insteon is also much faster than X10, and I believe that when you link a bunch of devices together into one scene, you can control that scene with a single powerline command.
posted by trevyn at 1:32 PM on December 4, 2005

FWIW, there are lots of solutions to this sort of thing that don't use a computer. Timers, light-sensing switches, remote-control outlet boxes, etc. If you must use a computer, well, that's something else.
posted by Kirth Gerson at 1:34 PM on December 4, 2005

The pattern with these power control technologies, even the ones that are supposed to have a low per unit cost, is that for the first several years they are only available as developers toolkits, usually in the $2K to $5K range.
posted by StickyCarpet at 1:42 PM on December 4, 2005

I'm quite sure what you are asking for exists as an off the shelf product in industrial settings, although wireless isn't too common yet because it isn't as reliable as wired. Industrial already means expensive, add uncommon to that and the price could be quite unreasonable.

There are some microcontrollers with embedded ethernet, so all you would need is a relay and a wireless to wired bridge (well, lots of secondary circuitry too, but...). There might be a hobbyist somewhere doing this, but I'm not deep enough in that scene to know where to look. You might try a search like 'wireless robot stamp'...
posted by Chuckles at 2:25 PM on December 4, 2005

You can get really cheap (< $20) uhf transmit/receive pairs that can do 9600baud rs-232. hang a tx off com1/ttys0 and buy an rx for each thing you'd like to talk to: a href="http://www.oatleyelectronics.com/remote.html">see here. There are also things there with 4-channel decode built-in, intended for alarms, they would require practically no external circuitry.

In the serial case, you will have to go to a bit of effort to decode the bitstream at each receiver. A PIC or AVR is probably the best option but if you're worried about the development skills, try a BASIC-Stamp - it's a PIC that runs a basic interpreter. Slow but good enough for what you need I think and very easy to write code for.

As for the 110V side, you MUST be opto-isolated. You can get some very nice relays with TTL-level inputs, opto isolation and a triac on the output (switches AC only) all in a single sealed unit, but they're not cheap. Ask for a "solid state relay" at your local electronics surplus joint and you may get lucky.
posted by polyglot at 4:16 PM on December 4, 2005

dammit, that got mangled.
posted by polyglot at 4:17 PM on December 4, 2005

You can get really cheap (< $20) uhf transmit/receive pairs that can do 9600baud rs-232. hang a tx off com1/ttys0 and buy an rx for each thing you'd like to talk to: see here. There are also things there with 4-channel decode built-in, intended for alarms, they would require practically no external circuitry.

It was the < in the < $20 that confused the HTML parser :(
posted by polyglot at 4:18 PM on December 4, 2005

I don't know why you want opto-isolation polyglot? Relays are already fully electrically isolated. Get one with safety agency markings (like the CSA or UL or VDE symbol) to be sure that it is built to a reasonable standard...

Then you need a power supply to drive the receiver and the relay coil, and a few transistors to buffer the receiver output so that it isn't overloaded by the coil.

Am I missing something obvious? I don't think so, but you never know...
posted by Chuckles at 4:33 PM on December 4, 2005

Well, I am missing the safety precautions... You have to be very careful with the AC wiring part:

1. Build it in a fully enclosed plastic project box with the relay securely mounted in the middle.
2. DC circuitry powered by a walwart on one side, AC circuit on the other side, there should be lots of space between them.
3. Live-wire-in to fuse to relay to live-wire-out, again all AC wire and components on one side of the box away from the DC circuit.
4. Heatshrink everything so that there is no exposed metal in the AC circuit.
5. Use strain reliefs or IEC connectors on the AC path so that there is no chance of fatiguing AC wires.

posted by Chuckles at 4:46 PM on December 4, 2005

If you're looking for a packaged solution, the terms you want to google are "802.11 I/O module". They are available for the industrial market, but they aren't exactly cheap. (You always trade price for ease of use). These will set you back a grand for the transciever and relay board.

Alternatively, you could buy a wireless USB server ex. 1, ex. 2 (which go for about $150 each), connected to a USB I/O module and relay board (probably another $200, including nice easy controller software).
posted by Popular Ethics at 4:47 PM on December 4, 2005

One solution using off-the-shelf AV control system parts would run probably around $2K equipment cost for this processor and this relay controller. The processor has an internal web server so you can just hook it to a wireless access point, then control from any computer with access to that network. This system is really powerful and can do all kinds of cool stuff, but it requires specialized programming, and it may be difficult to purchase this equipment. Another manufacturer of similar systems is AMX.

But wait! I just found something... This box does what you want, also has an internal web server, much simpler to program than the above. Again, program it and hook it to a wireless access point, you're ready to go. I think this one costs less than $1K.
posted by one at 5:31 PM on December 4, 2005

Here's an item that's not entirely off the shelf, but if you're a tinkerer and can figure out how to feed it your own program, it just might work, and for cheap.
posted by SteveInMaine at 6:35 AM on December 5, 2005

Dang, actually here's the direct lkink to the item.
posted by SteveInMaine at 6:36 AM on December 5, 2005

I'm also interested in home automation, specifically the type that can be controlled by computer. What are some reasons to avoid X10? What about security? Do I have to worry about some nerd hacking my house?
posted by electroboy at 6:47 AM on December 5, 2005

electroboy: I use X10 in my house to turn lights on and off at set times. In my view the problems with X10 are that it's slow to respond, and can be prone to interference, since it sends signals over your household power lines. Also, from my experience, the hardware is not terribly heavy duty and will occasionally fail. For instance, I don't own the thermostat module, but I understand that it really isn't very dependable. As a result, I would never consider using X10 for anything in the home that is mission critical, like let's say a security system or HVAC.

As for some nerd hacking your house, as far as I know, this is only possible if he's standing in your house with an X10 remote. Some folks have rigged up systems that allow them to send signals using a web interface, and I suppose this is as hacker-prone as an X10 system will get.

If you're really interested in the subject, a good place to start browsing around is the alt.home.automation newsgroup, or check out this guy's setup.
posted by SteveInMaine at 7:30 AM on December 5, 2005