Re: Controlling Holiday Lights

[sylvan butler <ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxxxxxxxx>]

On 2 Nov 2006 03:43:55 GMT, Dan Lanciani <ddl@danlan.*com> wrote:
> the specific triac trigger waveform you use for 50% power.  Could you
> describe it in terms of frequency and duty cycle or such?

It isn't a simple wave.  :)

I have not measured or attempted to calculate 50% power out of the
triac.  I don't have the scope out right now, so I just played a bit
with software...

Full speed alternating on/off (a 1:1 duty cycle, which produces a fairly
nice square wave on the gate) has no obvious effect on intensity.  A
full speed 1:4 (on:off) duty cycle noticably dims the light, maybe a 10%
power reduction.  At full speed with a simple wave (e.g. all on then all
off for regular periods) I cannot get down to a 50% power output without
flicker -- the off times are too long.

(This system was a C633 the last time I had the scope on the output, and
at that time full speed 1:1 produced a square wave of about 150khz,
IIRC.  Now it is PIII 750, but I expect that bus waits will keep the
output about the same since a k6-2/400 was also about the same.)

Crude rate limiting to approximately two samples per tick (reprogrammed
the timer to 1000 ticks per second) I can get lower power but I start
getting flicker somewhere around the 1:4 on:off ratio.  I expect
interrupt overhead is becoming significant and my delay loop between my
two samples per tick is very crude.

So now I go to a sample table where I can generate more complex waves...

Full speed using a 200 sample table I get an estimated 50% power (light
very orange, but still bright enough to fill the globe) when I do a
pattern with a duty cycle of about 1:2 (on:off) somewhat randomly
distributed within the table (it was actually 64 on, 136 off).  Using
the same table at 2 samples per tick (default frequency 18.x/sec)
results in very dim light, sometimes a bit of flicker.

Using a PIC it might be easier to sync with the zero-crossing and get
some determinism.  I've googled a bit, and syncing a PIC seems pretty
simple.  But I don't want to input that back to my PC parallel port.
Plus the real-time 120x/second is a bother.  I maybe should have saved
that data table...  :( Just keyed it all in directly to memory with
debug.)

sdb


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