Subject:
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Re: Smart Motor
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 14 Sep 2004 11:03:21 GMT
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Original-From:
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PeterBalch <PeterBalch@compuserve.com*antispam*>
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Viewed:
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1147 times
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> "Rob Limbaugh"
> Perhaps it would be cheaper to take a PIC and program it to behave as a
> DCC decoder?
Yes, I'd thought briefly about that.
It seems like it would be a simple circuit. Because there is AC available
at the DCC decoder, you probably don't need an H-bridge; just use two
transistors (and maybe some diodes?) - one to switch it on when the AC is
"forward" and one when it's "backward". (I haven't thought the design
through.)
I also wondered about a Triac or thyristor. I haven't designed anything
around either for many years. My recollection is that their voltage-drop is
considerable compared with a simple transistor.
Whatever the design of the decoder, it means that the central "brick" must
have a much beefier H-bridge driver for each chain of motors. If I'm
driving two motors then two H-bridges is cheaper. If I'm driving ten motors
then ten DCC chips may be cheaper. Where's the breakpoint?
A PIC10Fxxx plus a rectifier bridge plus two transistors plus some
resistors plus a pcb plus ... It adds up.
Plus a lot of development work.
> "Mark Riley"
> The
> $16US Digitrax DZ123 is actually quite a bargain
If the chips really are $16 then it's worth making your own. I can see that
for a Lego enthusiasts, a 2-wire bus is tremendous but, for the rest of us,
a three wire system also works well: power ground and a serial "control"
signal. The advantage of DCC would be a cheap ready-built controller chip.
> I believe most, if not all, decoder manufacturers use off-the-shelf
> microcontrollers (like the PIC) in their designs.
Aha. I hadn't realised. I presumed it was a single chip. I guess the market
isn't big enough (which is very surprising).
Peter
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