Re: Led lights

["David Buckley" <db@xxxxxxx>]

I've just had a quick shuftie inside an AM12

The AM12 uses a (single pole) pulse (sometimes called impulse)
relay, rather than a conventional relay.  Thus each time a control
pulse is applied to the relay coil, the relay changes state.  The
single pole switches the live line.  This is quite clever, as it
minimises the power consumption of the thing, reducing the heat
buildup.  (The relay uses a mains voltage coil, which is pulsed by
an SCR)

The corollary of using a pulse relay without an additional
"state"
monitoring contact is that the electronics has no way of knowning if
the relay output is on or off.  Which is bad, because (for example)
when you go "all units off" you expect the appliance module to
either (a) If its on go off, or (b) if its off, stay off.  Just
flipping state on principle would lead to some units going on, which
is not at all what is intended :-)

The solution embodied is to sample the mains output through a
resistor, and so when the relay is on there is voltage on the sense
resistor, and when its off, there isnt.  Thats the 80K explained.

And I suspect if you chop the brown wire which supplies the sensor
resistor (insert bomb defusing joke here) the device will change
state once and then be confused forever.  I cant test that, as this
particular AM12 (the only one within 10 miles of this keyboard) is
ferked, having died within a week of being used.

So, I cant see any good solutions involving simple hacking of an
appliance module.

Even so, this 80K would only allow 3ma to pass, which isnt much
juice, representing a mere 0.75W.

Solutions - all ugly.  External mains operated relay, with true dry
contacts supplying your LEDs.  Or use a universal module to switch
the low voltage side.

Dig at X10 time:  Whilst trying to find the name of the universal
module ('cos I'd forgotten) I was looking up www.smarthome.com,
which I find to be a really handy informative site.  And they ship
internationally.  But I digress.  I just loved this user comment
about the Universal Module:

"...I have used these for lawn sprinkler controls with approx 99%
reliability."

And thats why I hate X10.  It *almost* works...