Subject:
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Re: RCX & RIS, a fading glory?
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 4 Feb 2003 21:52:28 GMT
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Original-From:
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PeterBalch <peterbalch@compuserve.comSPAMLESS>
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Viewed:
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627 times
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John
> I think an ability to retain as much "Lego" infrastructure as possible is • to
> be desired. Mixing and matching alien non Lego wires and connectors • starts
> to depart the basic simplicity of polarity independence and Lego mechical
> compatibility
True. I was assuming that this was an alternative to the RCX.
I'm not a Lego purist; in fact, I'm working on a totally non-Lego
expandable system. For various reasons, I'd decided not to go down the
route we're discussing here but I'm not sure that those reasons were valid.
That's why I'm very interested in what other people have to say on the
topic.
I like the RCX style of a "brick" with ports which can connect to either
dumb sensors or dumb sensors with a few analogue components. Polarity
independence is only an advantage when you're trying to retro-fit
electrical connectors into Lego bricks.
What I've designed allows dumb input or output at a "port" or intelligent
input or output via "comms" at each port. As you say, an industry standard
bus is not of vital importance. The big disadvantage of something like I2C
or CAN is that the peripheral chip has to be able to accept comms input at
any time whereas it might well be busy servicing its sonar or whatever.
None of the chips I was considering (mainly the very cheap 8-pin PICs) can
do that. Comms shouldn't start until both sides are ready to communicate.
> data stream on top of the power
I suspect that noise from the motors will be a real problem so a very
robust protocol is required and probably low bit rates.
> There is about 1/2 square inch of board space
> fit both the sensor electronics and a communications
> single chip ... which can transceive** at >100kbps?
I'd use a PIC (but that's just because I always do). You'd have to invent
your own protocol. I see that Microchip have announced some extremely small
lead-less packages which are not much bigger than the silicon. I've just
looked through their CD but can find any exact dimensions. They say their
8-pin "TSSOP" package is 4.4mm square and the "Chip Scale" "MF" packages
are supposed to be even smaller. I certainly wouldn't want to hand-solder
one!
But a small 8-pin PIC will only run at 1Mips (with its internal oscillator)
and I doubt if you can write async comms s/w to run at better than 20kbps.
(Which is why I'd decided on a 2-wire bus and synchronous comms.)
Perhaps they have a small outline 16F627 (18-pin). It has a built-in UART
that I think will run at 16x the clock rate. Using the internal 4MHz
oscillator (i.e. 1Mips), that means 250kbps. (PICs need no external
components.) Would that fit your requirements?
There are supposed to be PICs which can do CAN bus and USB but I haven't
used then and I don't know if there are miniature packages yet. There are
also I2C PICs but I think they can only be master (while you want to be a
slave?).
Peter
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Message has 1 Reply:
 | | Re: RCX & RIS, a fading glory?
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| (...) Yes, I agree with that completely. I use them in all sizes for just about everything. The bit of "the scheme" I am trying to find a small single chip solution to is not the digital end of a comms link. As you point out, that's easy. The small (...) (22 years ago, 5-Feb-03, to lugnet.robotics)
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