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

[isw <isw@xxxxxxxxxxx>]

In article <hpqdncmhFKn1b9XVnZ2dnUVZ_gWdnZ2d@xxxxxxx>,
 "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:

> "Jeff Volp" <JeffVolp@xxxxxxx> wrote in message
> news:upJ1k.19034$102.546@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
> > news:hOWdnZPUEpdFotrVnZ2dnUVZ_jWdnZ2d@xxxxxxxxxx
> >
> > > I believe the first test will just be to simply disconnect pin 8 from
> the
> > > control line.  Hopefully it will be easy to rebridge if that turns out
> not
> > > to work.  Also, hopefully, it won't incinerate itself after snipping
> that
> > > line.  I guess I can trot out the old 20mm ammo box I have for
> containment
> > > of explosive experiments - well, maybe just leave it on a fireproof
> > > surface
> > > to test . . .
> >
> > Whoops, that was a typo before.  Pin 8 is used for the local control.
> > Snipping that will only disable local control.  Pin 6 drives the triac.
> > That line is essential.  If snipped there will be no on/off control at
> all.
> > The dimming phase control is inside the IC.
>
> As I understand it now, the pulse to the triac has to occur twice every
> cycle and has to be alternatingly negative and positive to allow each half
> of the AC cycle to pass.

The pulses do not have to alternate in polarity; that's one of the neat
things about triacs.

> The dimmer does its magic by narrowing the width
> of that pulse - shorter means less power gets to the device and its dimmer.
> As I said to Dan, I thought a triac was just a very fast solid state relay.
>
> > It might be possible to extend the pulse coming out of the IC so that if
> > there is ANY pulse at all, the transistor will remain on through the
> > beginning of the next cycle so the unit will switch on right after the
> zero
> > crossing.
>
> It sounds like the mod that uses the alternistor and the optoisolator does
> just that.  It seems that the optoisolator extracts the ZC data and then the
> additional circuitry creates its own full width pulse independent of
> whatever length pulse comes out of the IC.

It sounds like you're attributing too much functionality to the
optoisolator; it doesn't *extract* anything. It's just a transistor that
turns on when light shines on it. And the light is the LED that's inside
it. The output of the opto just repeats whatever is on its input while
isolating the possibly dangerous voltage levels on the input side.

> So if the module was dimming the
> output, it wouldn't matter because that pulse is driving a latching circuit
> that stays on until the next ZC, correct?

I don't quite follow you, but I don't think that's right.

The gate pulse (optically isolated or not) turns the triac on; the next
following zero crossing allows it to turn off. The "latching" part is
provided by the triac itself, because it's not necessary to continue
applying the gate signal after it's turned on.

Isaac