Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!exodus!oobleck.Eng.Sun.COM!bender
From: bender@oobleck.Eng.Sun.COM (Michael Bender)
Newsgroups: sci.electronics
Subject: Re: Light Dimmer
Message-ID: <3525@exodus.Eng.Sun.COM>
Date: 27 Nov 90 23:13:41 GMT
References: <2570007@hppad.HP.COM> <3450@exodus.Eng.Sun.COM> <1990Nov27.201653.4865@hayes.ims.alaska.edu>
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Organization: Sun Microsystems, Mt. View, Ca.
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In article <1990Nov27.201653.4865@hayes.ims.alaska.edu> ftpam1@acad3.fai.alaska.edu writes:
>In article <3450@exodus.Eng.Sun.COM>, bender@oobleck.Eng.Sun.COM (Michael Bender) writes...
>> 
>>A few years ago I built an 8-channel digitally-controlled dimmer.  I used an
>>8749 for the CPU [...]
>
>     Better yet, use an 8751 and do it all in software.  An 11 MHz 8751 can
>support 16 channels at 128 brightness levels.  It also has a serial port for
>easy interfacing to a host computer.
>
>     What did you use for a zero-cross detector?  My latest is an AC input
>optocoupler, but the current transfer ratio is critical for proper operation.
>(8751 port pins require a fair bit of current to pull down.)

At the time I was doing the dimmer I had an 8048 ICE for my S-100 system.
The 8051 ICE that my school had was under the control of some anal-retentive
type that couldn't see it being used to develop a "mere" light dimmer.
I think that guy is selling used cars now or something...

I used a transistor/resistor off of the p.s. transformer, and as I remember
it wouldn't really switch at the zero-cross point, but just a little after
when the transistor turned on (this was way back before I knew anything
about engineering!), so I couldn't get the triac on for the complete cycle,
but it was close enough that the lights looked like they were full on.  I
had plans to build this great digitally-controlled light board, but never
built more than the first 8 channel card.  Looking back on it, an 8051 would
have been a better processor to use, especially because of the built-in
serial port - I was using an 8-bit parallel connection between my 8048 and
the controlling computer.  I guess you just learn these things as time goes
on (this was in 1984 I think).

mike
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