Digital Control of Light
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Posts: 46,084
>
Original Message
> From: Chris Loiacono [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=2Sn7UXkVgTQVHRGM4SbpbUAwoMBrSuDjq0nBR_ndQFFH86EdhjDjry6-iqqb6TP5UvWcxLpaEztxC0jS]chris@m...[/url
> Sent: Friday, June 15, 2001 10:08 PM
> To: 'basicstamps@yahoogroups.com'
> Subject: RE: [noparse][[/noparse]basicstamps] Digital Control of Light
>
>
>
> >
> > Anyone have any suggestions on how to control brightness of a
> > 120vac 250
> > watt lightbulb using a BS1 or 2?
> >
> > Hey, I know it's probably a dumb question...
> >
> > Thanks.
> >
> > Rus
>
> Here's the cheapest way that I have found to control a 120V
> lighting filament with a stamp:
> Optocouplers are needed both to detect the zero-crossings of
> the AC line, and to fire the thyristor gate (I guess for
> this, a Triac is cheapest).
> The zero crossing detection can be accomplished with either a
> Schmitt or transistor output type optocoupler. The H11L1 is
> perhaps the easiest, and fast enough for the stamp (more on
> this in a minute)...There are also AC couplers that have two
> inverse LED's with one detector. With the earlier, you can
> set an input low, and use a pause and pulseout to output to
> your gate circuit. With the later, you'll get only a short
> detect output from the optocoupler when both LED's are below
> their thresholds. You can input this into the stamp pin also,
> if you prefer. For 120VAC, the straight transistor output
> lets you use SCR's, because you can use it to distinguish
> between the + and - 1/2 waves - which is needed if you want
> the full range of control.
> Put your pulseout into something like one of the MOC3010's
> (only OK for 120V, not higher), and have the 3010 output
> switch the line to the gate with a 180 ohm resistor in
> series. You can use whatever programming and interface scheme
> you like to change the pause that times the start of the
> pulseout. Use the shortest pulseout period that will gate the
> device consistently. If you use inexpensive TO-220 triacs,
> also consider transient protection for the triac.
> The shorter the pause is, the brighter the lamp will be. The
> biggest limitation is since the stamps are not so fast you'll
> only get a handful or two of steps of control - not unlike
> X10's dimmers. The cost is around $6.
>
> There's a PIC AN for higher resolution phase angle control
> without opto's. Everyone who has tried it has blown up
> several chips, so I have never tried it on a stamp.
>
> I also have done high-res phase angle control of
> large loads up to 480VAC with a PIC 18 at the heart of it,
> with soft start, current limit etc.
> I have adapted this to accept serial input from a stamp through
> a shift register for the power level command. It's a bit more
> complicated and costly. The PIC does most of the work
> If this is more like what you need, contact me off-list.
>
> I'm off to some GTO Thyristors for switching the power grid
> next. Anyone have any experience with these?
>
> Chris
>
> >
> > --
> >
>
Original Message
> From: Chris Loiacono [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=2Sn7UXkVgTQVHRGM4SbpbUAwoMBrSuDjq0nBR_ndQFFH86EdhjDjry6-iqqb6TP5UvWcxLpaEztxC0jS]chris@m...[/url
> Sent: Friday, June 15, 2001 10:08 PM
> To: 'basicstamps@yahoogroups.com'
> Subject: RE: [noparse][[/noparse]basicstamps] Digital Control of Light
>
>
>
> >
> > Anyone have any suggestions on how to control brightness of a
> > 120vac 250
> > watt lightbulb using a BS1 or 2?
> >
> > Hey, I know it's probably a dumb question...
> >
> > Thanks.
> >
> > Rus
>
> Here's the cheapest way that I have found to control a 120V
> lighting filament with a stamp:
> Optocouplers are needed both to detect the zero-crossings of
> the AC line, and to fire the thyristor gate (I guess for
> this, a Triac is cheapest).
> The zero crossing detection can be accomplished with either a
> Schmitt or transistor output type optocoupler. The H11L1 is
> perhaps the easiest, and fast enough for the stamp (more on
> this in a minute)...There are also AC couplers that have two
> inverse LED's with one detector. With the earlier, you can
> set an input low, and use a pause and pulseout to output to
> your gate circuit. With the later, you'll get only a short
> detect output from the optocoupler when both LED's are below
> their thresholds. You can input this into the stamp pin also,
> if you prefer. For 120VAC, the straight transistor output
> lets you use SCR's, because you can use it to distinguish
> between the + and - 1/2 waves - which is needed if you want
> the full range of control.
> Put your pulseout into something like one of the MOC3010's
> (only OK for 120V, not higher), and have the 3010 output
> switch the line to the gate with a 180 ohm resistor in
> series. You can use whatever programming and interface scheme
> you like to change the pause that times the start of the
> pulseout. Use the shortest pulseout period that will gate the
> device consistently. If you use inexpensive TO-220 triacs,
> also consider transient protection for the triac.
> The shorter the pause is, the brighter the lamp will be. The
> biggest limitation is since the stamps are not so fast you'll
> only get a handful or two of steps of control - not unlike
> X10's dimmers. The cost is around $6.
>
> There's a PIC AN for higher resolution phase angle control
> without opto's. Everyone who has tried it has blown up
> several chips, so I have never tried it on a stamp.
>
> I also have done high-res phase angle control of
> large loads up to 480VAC with a PIC 18 at the heart of it,
> with soft start, current limit etc.
> I have adapted this to accept serial input from a stamp through
> a shift register for the power level command. It's a bit more
> complicated and costly. The PIC does most of the work
> If this is more like what you need, contact me off-list.
>
> I'm off to some GTO Thyristors for switching the power grid
> next. Anyone have any experience with these?
>
> Chris
>
> >
> > --
> >
>
Comments
found the answers to my questions. I've been searching the archives for two
days. I've done my homework, so here goes . . .
I'm interested in dimming a 120V incandescent bulb (up to 500W) using a
power MOSFET and PWM from the STAMP. (In my experience TRIACS tend
to flicker especially at low illumination). Now my question has to do with
grounding. I would like to power both the STAMP and the bulb from the
socket in the wall. To do this I plan to use a 12VCT transformer and rectify
the
signal to power the STAMP and pass the 120VAC to power the bulb. The
stamp pulses the gate of the MOSFET which controls the bulb. Nothing to
extraordinary. Shouldn't ground (Vss) for the STAMP be the same as the
ground of the bulb?
1. Shouldn't the STAMP and bulb share a common AC-DC ground?
2. Must I use an opto-isolated gate?
3. Is there a way I can lose the transformer?
I don't want to use DMX.