Re: Making an X-10 lamp module immune to dimming

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"isw" <isw@xxxxxxxxxxx> wrote in message
news:isw-21C5D4.22184707062008@xxxxxxxxxxxxxxxxxxxxxxxxx

> > <stuff snipped>

> > Would another way to say that be the light level is determined by the
point
> > on the sine wave where the gate pulse arrives and that that unit stays
on
> > until the end of the cycle, no matter what happens afterward in that
cycle?
>
> It's the end of the next half-cycle (the next zero crossing), but
> otherwise, yes; that's what happens.

OK - this is getting clearer.  It doesn't conduct unless "goosed" by gate
current and once it's on, the gate current becomes essentially irrelevant
until the after the AC half cycle ends and the reversal of polarity shuts
off current flow through the triac.

> > So it's not possible to have a sine wave that has four "bands" of on/off
> > pulses?  Or is it just that way for the X-10 modules?  I thought, when
you
> > talked about pulses, that each one of them turned on the triac for a
tiny
> > bit of time, and that all of them added together in each cycle increased
the
> > power output.  That would require switch the triac on and off multiple
times
> > within the cycle.  That description is true of how all the chopped A/C
> > cycles add up, but I think you're saying the pulses that follow are not
> > having any effect on the state of the triac.
>
> Correct; they do not. Once a triac is conducting, it's very difficult to
> get it to turn off any way except removing the voltage across it
> (actually, it's removing the current through it that makes it turn off).

Are there other devices that can interrupt current flow with a gate trigger?

> > After reading more, what I envision now from your description is a
sliding
> > window sort of thing where the amount of current flowing depends on how
far
> > you slide the ON window to the left-most window stop, which in this
case, is
> > the zero crossing.  That sound anywhere near right?
>
> Right on. But think about how a half-sine looks -- a linear increase in
> on-time does NOT result in a linear increase in power delivered to the
> load.

Right.  This looks very much like an "area under the curve" sort of problem.

> > > > I assume that would me they are obviously much shorter in
> > > > duration than 1/2 the AC cycle.  It sounds like they are
"rechopping"
> > the
> > > > pulse into smaller pulses and that they aggregate to give the
desired
> > end
> > > > level.  I am not explaining that well, I fear.   It seems like there
are
> > two
> > > > pulse aggregations, a wheel within a wheel Ixion sort of thing.
> > >
> > > The fact that there is a train of pulses is probably an artifact of
the
> > > way the IC in the X-10 unit accomplishes phase delay (to retard the
> > > timing of the gate drive).
>
> There is exactly one "on" interval per half cycle;

My "one chop per hump" interpretation.  (-:

> if it is very short,
> no appreciable power is delivered to the load. If it is nearly a full
> half-cycle in duration, nearly full power is delivered.
>
> > So it might even be possible it's really just noise with no particular
> > function but no particular harm to the operation of the module.
>
> It's not noise; it's a regular string of pulses.

I thought that any signal other than the one you wanted could be considered
noise.

> > I assume you detected it with some sort of logic analyzer?
>
> No; just an ordinary oscilloscope.

I guess it's time to finally unbox my Radio Shack pen oscilloscope.

<stuff snipped>

> > > I was interested in using X-10 units to remotely control stuff other
> > > than lamps and coffee pots. Getting an optically isolated variable
width
> > > pulse was a good starting place. I was not going to use that signal to
> > > drive a triac in amy way.
> >
> > Sounds interesting.  Wouldn't such an extension give you trouble with
> > standard repeaters?
>
> I didn't care about repeaters. What I wanted to do was control a large
> number of electrical valves for an irrigation system. As I said, the
> problem was that it was not repeatable -- the same number of "brighten"
> pulses did not always result in the same pulse width, and so I could not
> reliably select which irrigation circuit I wanted to run.

Too bad.  What's a large number?  There's a lot of headroom with 256
discrete X-10 addresses, even if you're controlling a modern home.


<stuff snipped>

> > So with the capacitor, the signal is being smoothed out from a pulse
train
> > to voltage level.  Usenet II is going to need a whiteboard.  At least
ten
> > times now I've wanted to show something with a simple sketch.   What
does
> > that pulse train look like?  Is it a square wave with the lowermost part
at
> > 0 volts and the uppermost part at Vcc+ (not sure if that the right
term).
> > Would the resulting DC level be Vcc+/2 or something close to that?
>
> Honestly, I don't remember. I was doing this some years back. All I
> recall is that starting from "full dim" there was one narrow, "square"
> pulse, very close to the following zero-crossing. As "brighten" pulses
> were sent, that pulse always moved earlier in the half-cycle, but as it
> moved, it was joined by progressively more and more that looked just
> like it. The "extra" pulses occurred later in the phase than the one
> that turned the triac on, and so they had no effect on the operation of
> the unit.

Interesting.  I assume that with X-10's parsimonious Scotch heritage that
they decided that as long as it didn't have a negative impact on
performance, they didn't need to add any circuitry to filter it out.

> > > > > 2) Change the 2.2 k resistor to 12 k.
> > > >
> > > > You would normally change a resistor value to change a time value in
a
> > > > dependent RC circuit or to protect some other component from drawing
too
> > > > much current, correct?
> > >
> > > Yup. In this case, I raised the value to allow a smaller capacitor to
be
> > > used to get the time constant I wanted.
> >
> > At least I remember that much from reading my 555 cookbook 20+ years
ago.
> >
> > > > > 3) Connect a 0.1 mfd. capacitor (ceramic is fine) from the cathode
of
> > > > > the diode to V-
> > >
> > > That's the cap that integrates the pulse train into a DC value
> >
> > You said "average DC level" before.  Is it safe to assume that DC value
is
> > still going to show some trace of the underlying pulses because of how
it
> > has been generated?  Is that called ripple or is that something else
> > entirely?
>
> Ripple would be a good term to use. The trade-off is that as you
> increase the time constant to reduce the ripple, you also increase the
> time the unit takes to respond to changes in the pulse width.

This sounds like one reason that circuit designers are always tweaking the
values of capacitors and resistors between board versions:  to optimize the
various design trade-offs.  (-:

> > > > > 4) Change the 330 ohm resistor to 2.2 k
> > >
> > > Simplistically, the 12K resistor determines how fast the cap charges
> > > (but not discharges, because the diode prevents that), while the 2.2K
> > > controls the discharge time.
> >
> > Is that capacitor discharging during the time the pulse is at zero, thus
> > providing current in the circuit where there would have been none
without
> > it?
>
> Yup.

It seems as if the R/C circuit is one of the most common electronic
"building blocks."

<stuff snipped>

> > Thanks for the encouragement and the input.  I feel a little like I felt
on
> > the first day of kindergarten when I saw all the sixth graders writing
in
> > cursive, reading big books and most impressive of all, taking the stairs
two
> > at a time!
> >
> > I suppose this means I'll have to finally break down and open an account
at
> > Digikey or Mouser.  (=;
>
> Learn how to take old gear apart and scavenge the parts. Not only do you
> get all sorts of good stuff, but you improve your (un)soldering skills
> at the same time.

I've been stripping components for a long, long time. When something like a
stereo breaks, I put it aside until it's obsolete (that wasn't really the
plan, but that's what always happens).  Then I strip out the more useful
looking parts.  Now, perhaps, I can finally *do* something with them.  I've
been toying with the idea of making an interface to Jeff's XTB to read the
raw data bits from the line into a data file.  He assures me that it's as
easy as pie, but I am not so sure.  The problem is that my meager
bitwhacking and soldering skills stand in the way!  I think first I will try
to trace and document the lamp module as thoroughly as I can.  I'll do that
in a separate thread after a do some searching to make sure it hasn't
already been done to death.  Something tells me that by tracing the circuit
through, I'll pick up a lot that didn't sink in just reading the protocol
docs.

Thanks again for all the help.

--
Bobby G.