>  Sure ya can, it's done all the time in message board type
>signs..  With up to 5K+ bulbs you need zero crossing to keep
>life reasonable, and you also need dimming for night.  Just
>don't fire the triac on the negative (or positive) side of
>the cycle and you get ~50%.

Something my partner reminded me of when reading this (he used to design
exactly that before we set up shop) is to be sure to change polarity every
so often.  He used to try to ensure that about 50% of the lit bulbs ran from
each half cycle and changed the polarity every few seconds.  These were
time/temperature displays based upon the 1802 (gad!) - the display was
pretty static.

Oh - he said the reason for changing polarity was to reduce corrosion when
the backs and bases of the lamps got wet (he also emphasised WHEN, not if!).

dwayne


Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 15 years of Engineering Innovation (1984 - 1999)

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