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From: Fred Bloggs
User-Agent: Mozilla/5.0 (Windows; U; Win 9x 4.90; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0
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Subject: Re: Triac controlled holiday lights
Date: Mon, 02 Dec 2002 03:41:33 GMT
NNTP-Posting-Date: Sun, 01 Dec 2002 19:41:33 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Steve W.EE wrote:
> 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
> in series.
> The idea occurred to me if I could drive the bulbs
> at half voltage I could cut them into segments of
> 25 bulbs.
> 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 @ )
Something like this is cheap. You put a toggle FF in front of your opto
and toggle with each line cycle.
View in a fixed-width font such as Courier.
LINE------------| 25 BULBS |----------------+
| \ / 300V
| --- DIODE
| OPTO |
| +--------+ |
+-O----+ | | 180 |
FROM |clr Q|---+-+ --+-----/\/\---+
+ ZERO ---> | |-+- | | |
XING | TFF | |\ / +- | |
DET | | |--- | | |
| | | + +-+ | ----- TRIAC
+------+ | | +-+-------\ /\ \/ or
+-+------+ G ----- SCR
-----------+ | |
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