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Date: 2 Dec 2002 01:10:23 -0000
From: Steve W.EE
Author-Address: stevew-ee nym alias net
Subject: Triac controlled holiday lights
I have been building a circuit which will flash
holiday lights. It has 14 pairs of optocouplers/
triacs to control 14 strings of lights. So
far this is working well but I'm considering
a last-minute redesign.
Each letter in the display has from 10-20 lights
in it. In the past I was able to get strings
of 100 lights which were wired in 5 circuits of
20 bulbs. We'd put the bulbs we want in front
then hide the remainder of the 20 in the back.
Problem now is that all the strings of 100
mini-lights are wired in 2 groups of 50 bulbs
The idea occurred to me if I could drive the bulbs
at half voltage I could cut them into segments of
One obvious solution would be to put a diode in
series with each string of bulbs. I don't see
a problem with this does anyone know why having
a triac switch a recitifed load would be bad?
Would there be any advantage in alternating the
polarities of the diodes on each string of
What about a single diode in series with the common
return wire, of a suitable amp rating like 5A, which
would rectify all the loads?
Another option would be to pull out the triacs and
pop SCR's in their place. They are in sockets but
the board cannot be rewired. The triacs in TO220
have gate on one side going to the opto thru a 1K,
MT2 in the middle going to hot AC, and MT1 on the
other end going the load. The other side of the
goes to the MT2/hot AC.
Are SCR's in TO220 pinned out so they could work in
the same socket and also rectify the AC?
Any other ideas. I think using high power resistors
might be messy but thought of using larger bulbs like
1-watt as reisitors. Of course the larger bulb would
not be fully heated so it's resistance would have to
be experimented with.
Steve W. stevew-ee.nym@alias@net ( interchange . and @ )
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