I am a novice and would like to build a 120V AC outlet which can be switched
on and off by USB. I'm not sure what all I will need and want to make sure
that I'm not trying to do something much harder than it sounds. My end goal
is to have a single plug where I could plugin a lamp, TV, power strip, etc
and have the power to that device controller by a PC via USB port. Now I've
seen some devices out there like X10-compliant home automation controls and
there has always been a severe limitation in one way or another. I would
love the pulg to be grounded but it doesn't have to be if that is a
complicating factor.

It seems to me that I need a relay which can switch the 120V on/off and then
need a USB controller to control the relay. And I have seen USB controllers
which have serial interfaces on them but then how to get from a pin or two
of a serial port to the relay is where it breaks down in my head. I'm not
sure what I need between the two or if that would even work. I can handle
the software part of it once I get a hardware solution idenfitied.

Can any of you pros offer advice to get me going in the right direction?

Thanks!
Frank

Easiest way I can think of - get a FTDI 232R chip, hook up DTR to an
opto-isolated triac driver, to a triac, to the power.

Then, at least on Linux, you can toggle DTR just by changing the baud
rate to 0 (dtr off) or anything else (dtr on) via "stty" or the
termios() functions.

The FTDI chips also have some GPIO pins you can use; in theory you can
control six outlets with one chip that way (four GPIO, plus DTR, and
RTS). You'd need to use their DLL and API to do that, though. Not a
big deal if you know how to do any programming; the API is pretty
straight-forward.

You can even get a vanilla USB to Serial adapter cable, and use DTR
off that.

I have some triac circuits here:
http://www.delorie.com/house/furnace/

But the opto-triac-power circuit is pretty common; you should be able
to find schematics all over the web. I think the triac data sheets
usually have schematics too.

Beware - messing with 120v power is dangerous. This isn't a
beginner's project, although I think most beginners successfully pull
it off anyway. I know I did

<noreply@noreply.net> wrote in message
news:K_udnQr1k4NwjOHanZ2dnUVZ_oimnZ2d@giganews.com...
>I am a novice and would like to build a 120V AC outlet which can be
>switched
> on and off by USB. I'm not sure what all I will need and want to make
> sure
> that I'm not trying to do something much harder than it sounds. My end
> goal
> is to have a single plug where I could plugin a lamp, TV, power strip, etc
> and have the power to that device controller by a PC via USB port. Now
> I've
> seen some devices out there like X10-compliant home automation controls
> and
> there has always been a severe limitation in one way or another. I would
> love the pulg to be grounded but it doesn't have to be if that is a
> complicating factor.
>
> It seems to me that I need a relay which can switch the 120V on/off and
> then
> need a USB controller to control the relay. And I have seen USB
> controllers
> which have serial interfaces on them but then how to get from a pin or two
> of a serial port to the relay is where it breaks down in my head. I'm not
> sure what I need between the two or if that would even work. I can handle
> the software part of it once I get a hardware solution idenfitied.
>
> Can any of you pros offer advice to get me going in the right direction?
>
> Thanks!
> Frank

http://www.futurlec.com/Relay_4.shtml

and

http://www.futurlec.com/USB.shtml

You will also need a 5V wall adapter to power the relay board.

About $50 not counting the adapter.

The problem will be building the interface between the USB module and the
relay card.

I can't tell from the specs in the link, but the USB module can probably be
programmed to make pins go up and down. They claim to have "Easy Setup and
Full Instructions".

I'm also guessing here, but the relay card probably uses a single pin per
relay as control. When it goes to 5V, the relay closes, when it goes back to
ground, the relay opens.

If you are lucky, the USB card will output enough power for the relay card,
and you won't need the adapter/plug.

Send a question to the Futurlec guys here:

http://www.futurlec.com/Help.html

They have been very helpful to me in the past.

Good luck.

Regards,
Bob Monsen