Subject:
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Re: Project WIRRL Update
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 21 Oct 2002 12:12:53 GMT
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Viewed:
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1050 times
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I'm looking for an RF solution for PC-RCX communication as well, been
thinking along very much the same lines as Rob seems to have so far, I too
was pondering how to deal with TX/RX switching (though I've not got as far
as building a circuit, and was tempted by the PIC route). But I've just had
a thought. Rather than build a custom circuit to do the IR-RF and RF-IR, why
not use the Lego serial tower and build (or buy) a full-duplex RF - RS232
solution?
Commercial ones seem to be available -
http://www.aerocomm.com/Pkg/connexlink.htm, for example, but the few prices
I could find all seem to be around the $200+ mark. Too much for me, and the
units tend to be quite large by Lego standards anyway, and probably aren't
optimised for low power consumption.
I'm sure a simple one could be made, by using cheap transmitters and
receivers on 2 separate frequencies (ie not using single-frequency
transceivers, which is what I'd been thinking along the lines of till now).
This sould allow full-duplex operation at a more reasonable cost. Encoding
may well be required for the sake of reliability as no echo back from the
tower would be bad (does the tower use the RTS / CTS lines? If so it ought
to be easy enough to implement encoding).
Probably 1.5x the cost of a pair of transcievers (and half that again with
four encoding/decoding chips), but it'd eliminate all the TX/RX switching
stuff, 38KHz modulation circuitry, LEDs etc. and associated costs (not to
mention design headaches!). You'd need two antennas, and the risk of
interference would be doubled, and there may be added complexities I've not
seen yet, but something like this ought to work.
It may be possible to fit the additional circuitry inside the tower itself
with a bit of hacking, which would create a rather nice little module - the
RF kit could run off the 9v battery and you could keep the serial connector
and fit a switch to change between RF and serial. Oh, and you'd have to
connect the pins that are used to identify the tower on the PC transceiver
box so PC software would think the tower was there.
Might there be issues with latency if you used encoding? I wouldn't have
thought so...
A quick look on the web suggests the transmitters and receivers would come
to around $60, with another $40 for four serial encoding/decoding chips.
Tim
"Rob Limbaugh" <lego-robotics@crynwr.com> wrote in message
news:000f01c278bb$abf73e80$650ba8c0@markera...
> Hello everyone,
>
> WIRRL stands for "Wireless Infra-Red Radio Link".
>
> Creating each leg of the RF link independantly isn't really a problem • (once
> you have a reliable 38kHz IR carrier wave). The problem is eliminating • link
> feedback by controlling the direction of the conversation.
>
> Because it had been a couple months since I was last able to play with
> things, I decided I should probably document where I am now. (Spending
> yesterday going back over my notes was sort of a drag...) Then, I had • this
> radical idea of sharing things (what a concept!?).
>
> [The real story: I couldn't find everything. The stuff I did find was • out
> of order or in multiple places. I couldn't read some of my own notes, and • I
> had to rebuild some things so I could remember what they did!]
>
> So, for those interested:
> http://www.abs-robotics.com/projects/wirrl.htm
>
> Be warned... the current schematic probably won't work if you build it
> (matter of fact, I'm willing to bet it won't). The diagram looks like • it's
> made from different resources... that's because it is.
>
> Today I was working with a possible half duplex communication switching
> solution, which is set to be controlled by a 4001 NOR gate. A 200us delay
> is set for both sides of traffic. So, when the RX side is re-transmitting
> IR data, the 4001 is supposed to turn off the data line for the IR decoder
> (which feeds the RF TX) and hold it off 200us after the line goes low so
> feedback doesn't occur. This is where I'm currently stuck. Sadly, I'm • not
> an electronics guru, so it will take me some time to figure things out.
>
> Any guidance would be welcomed!
>
> - Rob
>
>
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Message has 1 Reply:
 | | Re: Project WIRRL Update
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| Replying to myself... I dismissed commercial solutions (proper radio modems) because they all looked too expensive. But I've found a beauty: (URL) RS232 @ 38.4Kb full duplex, 15Kbit rf, integral antenna, just under £30 (~$50) each for single units. (...) (22 years ago, 21-Oct-02, to lugnet.robotics)
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Message is in Reply To:
| | Project WIRRL Update
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| Hello everyone, WIRRL stands for "Wireless Infra-Red Radio Link". Creating each leg of the RF link independantly isn't really a problem (once you have a reliable 38kHz IR carrier wave). The problem is eliminating link feedback by controlling the (...) (22 years ago, 21-Oct-02, to lugnet.robotics)
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