Subject:
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Re: sending signals over power lines
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 28 Dec 1996 04:44:15 GMT
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Original-From:
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Tom Vanselow <vanselow@NOMORESPAMexecpc.com>
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Reply-To:
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VANSELOW@spamcakeEXECPC.COM
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Viewed:
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1495 times
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Andrew S. McGeachie wrote:
>
> hello. While this question doesn't pertain directly to the handyboard, I
> thought I would post it here since I am using the handyboard in my project.
> Some of you may have heard of this product: There are devices on the market
> (radio shack and a few others sell them), that are used for controlling
> appliances and lights remotely, and they work by sending signals over the ac
> power lines in your house. That is, you plug a special controller unit into
> an ordinary outlet in your house, and replace the things you want to control
> (a light switch for example), with special funky light switches. The
> controller box can then turn the light on and off by sending signals over
> your house current, which the special light switch can receive and respond to.
>
> Now what I am wondering, is how exactly is this done? How are the signals
> encoded? Is AC required or can this be done over DC as well? I'm
> interested in doing something similiar, just not with appliances and house
> current.
>
> Thanks for any help.
>
> - andrew
Andrew,
I've putzed around a bit with the system you've discribed. Its called
X-10 power line carrier transmission. (P.L.C.) The codes format was
setup back in 1978 for Sears and Radio Shacks Plug 'n Power system.
Since then X10 Powerhouse has many other companies using thier code
format as well. The transmissions to the control modules is done on the
AC power line of your house. Each module has a two dials on it for
programming a "House" code and a "Unit" code. Each dial has 16
positions, thus 256 different modules can be accessed. Thier are dimmer
modules, appliance modules, burglar alarm interfaces, and a veritable
plethora of other devices made to interface with this system.
The theory behind the system is pretty simple. The X-10 transmissions
are synchronized to the zero crossing point of the AC power line.
Binary codes are transmitted down the power line by gating 1mS bursts of
a 120KHz square wave onto the power line. A binary 1 is represented by
a 1mS burst at the zero crossing point, and a binary zero is represented
by the absence of the 120Khz burst. The 1mS bursts are actually
transmitted three time per half cycle to coincide with what would be the
zero crossing points in a three phase system as well.
Sending an X10 code requires a minmium of eleven cycles of the power
line. The first 2 cycles are called the start code, the next four are
the house code, and the last five are the unit code or function code.
It gets a little complex to discuss the details here but the good news
is that the system is well documented. Radio Electronics magazine did a
neat project called the "Phonlink"
years ago and they had several articles which explianed the system.
The hardware needed to send the codes is easy to setup. A 555 timer can
be setup to oscillate at 120Khz. Its output is feed into one input of a
TTL AND gate, and the other input to the AND gate is tied to a
microprocessor digtal output (such as the handy board). The AND gates
output is sent through a coil of wire (inductor) wrapped around the
power line. A seperate circuit is then used to detect zero crossing on
the AC power line and provides the microprocessor with a 120Hz square
wave input to use as a timing reference. After a little programming,
you can control almost anyting in your house. By the way, the handy
board is well suited for this application.
I'm not sure if you would have much luck using the X-10 modules on a DC
system, due to the fact that they probably sense zero crossing as well
to receive codes.
Good luck with your project
Tom Vanselow
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Message is in Reply To:
 | | sending signals over power lines
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| hello. While this question doesn't pertain directly to the handyboard, I thought I would post it here since I am using the handyboard in my project. Some of you may have heard of this product: There are devices on the market (radio shack and a few (...) (28 years ago, 27-Dec-96, to lugnet.robotics.handyboard)
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