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

[isw <isw@xxxxxxxxxxx>]

In article <rYadnVE6-IgY-tfVnZ2dnUVZ_rbinZ2d@xxxxxxx>,
 "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:

> "isw" <isw@xxxxxxxxxxx> wrote in message
> news:isw-988B8E.10385606062008@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> <stuff snipped>
>
> > > > A while back, I hacked around in those controllers. Here are some of
> my
> > > > notes:
> > > >
> > > > "The IC generates a series of pulses, with at least one always
> present,
> > > > near but before the zero-crossing (i.e. even at "off" the triac is
> > > > triggered, just very late in the half-cycle).
> > > >
> > > > "As the "brighten" signal is sent, the pulse first slides earlier in
> the
> > > > half-cycle, and then multiple pulses appear, with more and more as
> full
> > > > on is approached."
> > >
> > > Does that mean that the pulse width does not vary, but that the level of
> the
> > > light is determined by how many pulses of a fixed width are received
> during
> > > an AC cycle?
> >
> > The level of light is determined by when the leading edge of the
> > earliest pulse arrives. The other pulses have no effect.
>
> 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.

> 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).

> 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.
>
> > > 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; 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 assume you detected it with some sort of logic analyzer?

No; just an ordinary oscilloscope.

> > > > What I wanted was a single duration-modulated pulse (wider for
> brighter,
> > > > of course), and here's how I got it:
> > >
> > > Why did you want to do this?  What is the benefit of going to pulse
> width
> > > from their system of number of pulses per cycle?>
> >
> > 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.


> > > > 1) Add a signal diode (1N4148) in series with the signal from IC pin 6
> > > > (i.e. cut the trace and hook it between the two points "B" on the
> > > > schematic, cathode towards the transistor)
> > >
> > > Bear with someone with no experience but at least a little interest in
> the
> > > subject.  That's a high speed switching diode, AFAICT, and used in
> series it
> > > will pass current in only one direction . . .
> >
> > Yup. It allows the pulses from the IC to pass into a capacitor (for
> > filtering them to an average DC level), while preventing the internals
> > of the IC from (possibly) drawing a current that would prevent taht
> > filtering from taking place.
>
> 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.

> > > > 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.

> > > > 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.

> > > I've already discovered that X-10 gear has naked 110VAC running all over
> the
> > > circuit boards, making tinkering by noobs like me a lot more dicey than
> > > trying to solder remote contacts to a coin cell powered keychain
> controller
> > > circuit board.
> >
> > True, but if you're careful to make sure it's not plugged in while you
> > have your fingers in it, there's not much to worry about. There are no
> > components in there that can store large chunks of energy, for example.
>
> I learned that lesson with an 555 design that reversed an agitator motor by
> charging up a fairly large capacitor.  They bite.
>
> > Keep on hacking; that's the way to get better and more confident at it.
>
> 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.

Isaac