Newsgroups: comp.robotics
Path: brunix!bullwinkle!jak
From: jak@cs.brown.edu (Jak Kirman)
Subject: Re: Looking for low-cost wireless data link
In-Reply-To: laird@pasture.ecn.purdue.edu's message of 12 Feb 93 00:35:15 GMT
Message-ID: <JAK.93Feb12013920@aruba.cs.brown.edu>
Sender: news@cs.brown.edu
Reply-To: jak@cs.brown.edu
Organization: Dept. of Computer Science, Brown University
References: <C2AyAu.J35@world.std.com> <laird.729477315@pasture.ecn.purdue.edu>
Date: Fri, 12 Feb 1993 06:39:20 GMT
Lines: 34

In article <laird.729477315@pasture.ecn.purdue.edu> laird@pasture.ecn.purdue.edu (Kyler Laird) writes:
[Someone wanted low-cost wireless transmission -- who doesn't? :-)]
>
>   Hamtronics, Inc.
>   65-D Moul Rd.
>   Hilton, NY  14468-9535
>   Voice: 716-392-9430
>   FAX: 716-392-9420
>
>   1200 and 9600 baud units/modules for a few hundred dollars.

Does anyone have experience with these?  We use Arlan (address on
request), who sell these things for 1-2K, depending on the
configuration.  What I really want to know is how worthwhile all the
error-detection/recovery software is; the Arlans will do this completely
transparently, and can pick up dropped connections without too much
trouble.  We find the transfer rate drops dramatically if you transmit
small packets; in the worst case of something like tip that wants to
echo each character, we end up with around 1200 baud.  Turning off
echocheck in tip gets it up to 7600;  I believe the specs claim a
maximum rate of 9600.

The Arlans work pretty well unless there is some *large* body of
metal between the transmitter and the receiver, like an elevator shaft,
or a fire door (fire doors only cause problems when the distance is also
fairly large).  The maximum distance we use them for is under 50m.

How much error-correction would be necessary with these cheap versions? 
How painful is it to write the software to produce a transparent serial
interface? 
                         Jak Kirman                        jak@cs.brown.edu
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are three ways to get something done: do it yourself, hire someone,
or forbid your kids to do it.
