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

[isw <isw@xxxxxxxxxxx>]

In article <08F1k.18467$102.2347@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
 "Jeff Volp" <JeffVolp@xxxxxxx> wrote:

> IC pin 8 is the output that drives the triac.  The delay of that pulse with
> respect to powerline zero crossings determine the brightness.

Actually, I think it's pin 6 that drives the triac, via C337 (assuming
that schematic is correct).


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."

What I wanted was a single duration-modulated pulse (wider for brighter,
of course), and here's how I got it:

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)

2) Change the 2.2 k resistor to 12 k.

3) Connect a 0.1 mfd. capacitor (ceramic is fine) from the cathode of
the diode to V-

4) Change the 330 ohm resistor to 2.2 k

--

As an interesting side-note, connecting the LED of a *high voltage*
optical isolator in series between the 39 ohm resistor and the collector
of C337 will give a safely isolated version of that pulse (or the
original pulse bursts, if that's what you want).

--

Now, to go on to an "on or off" version, here's what I'd try (Note that
I haven't done it, so I'm just guessing here):

Replace transistor C337 with a very high-beta Darlington transistor
(that will make for a much narrower "linear zone" between cutoff and
saturation.

Increase the size of the added 0.1 mfd. capacitor until the base signal
to C337 is integrated to a DC level (which will rise as the pulse
widens).

So now, the transistor should move from off to on at some fairly well
defined pulse width (adding some feedback to make the C337 act like a
Schmitt trigger will help).

IF this works, it will almost certainly have some "lag" because that cap
has to charge or discharge before the triac gate signal can change.

It'll surely take some fiddling around to find optimum values for some
of the added parts (but having that optically-isolated signal to look at
will make the process a whole lot safer). Maybe a cap from the collector
of C337 to V- would help. Maybe adding a couple of forward-biased diodes
or a low-voltage zener in series with C337's base (to increase the
voltage where it starts to turn on, something the Darlington also does).
I'd try it both with and without that 1N4148,  too.

CAUTION. WARNING. If anything you do as a result of trying to follow
these notes gets you injured or dead, or kills your cat, or burns your
house down, I'll be very sorry, but I will *not* be responsible. I'm a
professional engineer who has been doing things like this (or worse) for
well over forty years. You get to decide for yourself whether your level
of competence is sufficient for you to tackle it.

Isaac