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

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dan Lanciani" <ddl@danlan.*com> wrote in message
news:1348348@xxxxxxxxxxxxxxxxxxxxxx
> In article <VtCdnaFcKJIC0NfVnZ2dnUVZ_rPinZ2d@xxxxxxx>,
ROBERT_GREEN1963@xxxxxxxxx (Robert Green) writes:
>
> | As I looked at the mod schematic, I realized that the switching was
> | occurring without any polarity reversal of the trigger.
>
> No, you were right the first time.  The direction of the gate current is
> reversing in step with the line, keeping the triggering in the more
sensitive
> quadrants.

I'm going to have to trace this out through the schematic.  Do you know of
any tools that do a "schematic debugging" the way some software debugger
tools work where each line of code executes in a window that displays
variable states, etc?  I've heard designers talk about simulators but I
don't know what they use or how it works.  I would like to see something
that would tell me what a voltmeter/scope/logic probe would see at a
particular point in the circuit for each state change.  Not sure I explained
that well . . . Anyway, so you're saying if I were to put a probe on that
line going to the triac gate, it would be DC pulse; positive when applied to
the first half of the AC cycle and then negative for the second half?

> The unmodified module uses its own DC supply to drive the gate
> current independent of the line polarity.  Using the more sensitive
quadrants
> (or, in general, using two quadrants with the same sensitivity) keeps the
> triggering times as symmetrical as possible minimizing the DC component in
> the output.

I'm confused again.  If I applied the probe on the unmodified mod, would I
only see positive pulses?

> | I am assuming that
> | the pulse has to be given after each ZC because the triac has turned
itself
> | off because of a lack of current flow.
>
> You assume correctly.

Slowly, it's becoming more clear how these things work.

> | I worded that badly.  I should have said that the support circuitry in
the
> | mod detects the ZC and then feeds that to the optoisolator which then
pulses
> | the triac with power that is independent of the existing module
circuitry.
>
> Again, you were right the first time.  This optoisolator has extra
circuitry
> to synchronize with the zero crossing.  Although the output of the
module's
> IC is synchronized to the line, once it is integrated and passed through a
> threshold detector there is no guarantee that the resulting transition
will
> be anywhere near a zero crossing of the supply.  The MOC3042 insures that
> the switching will happen only near the zero crossing.  Note that we are
> talking about the single transition from off to on when the module is so
> commanded, not a transition that happens twice per cycle.  Whether this
> is important is up to you.
>
> | I assume that's done because of the line voltages involved and to
prevent
> | any unintended interaction of the modification circuitry with the
module's
> | circuits.
>
> I suspect you are correct.  The zero crossing synchronization is just an
> extra (but nice) feature that comes for free with a part that happens to
> do just what is needed for the modification.

Neat.  The whole concept of AC current is pretty interesting.

http://en.wikipedia.org/wiki/Alternating_current

I think I have a bit of reading to do but I am thinking the lamp module is a
small enough device to trace out thoroughly.  Maybe I can even bring myself
to trying the mod in question to make them into "dim-free" devices.

Thanks for the explanations.  They might even sink in - eventually. (-:

--
Bobby G.