Re: TINI wireless link - IR or RF?

At 10:27 AM 6/29/2004 +0100, Simon Melhuish wrote:
>Hi.
>
>I've been given with an urgent interfacing job, that will require 
>communicating wirelessly with a battery-powered TINI (or similar). Can 
>anyone suggest where I should start?
>
>The basic requirement is short range (< 3m) so I'm thinking IR. Also it's 
>going to be pretty dark (South Pole during the winter) which I suppose may 
>help. If I went RF I'd have to take care about interference. The data rate 
>need not be high (say 9600 Baud), but should be bidirectional.

Short range RF or special long range IrDA might work. IrDA is only 1 meter 
guaranteed and the angle is quite narrow, something like 10 or 15 degrees 
in a cone. RF could be 360 degrees of coverage.

RF is typically by nature half duplex. So a 19200 baud modem might work 
depending on your data packet size and rate. 9600 baud is 960 bytes/sec 
max. Any packet overhead cuts this down.

RF modems need some few msec to switch from transmit to receive, too, and 
have some overhead with preamble, CRC, etc, just like ethernet.


>I've seen some mention of irDA on this list in the past, but most often as 
>a work in progress. Can anyone tell me of any off-the-shelf ready-to-go 
>gear for this kind of thing? I need to have something running by Christmas 
>at the latest.

IrDA doesn't have the range you need. It's 1 meter by the spec.

You can buy the modems today from Maxstream, and their dev kit with serial 
interfaces. We will have JSimm carrier boards soon after JCX is really 
shipping. But the dev kit from Maxstream.net works great and will do 
everything you need.

You could cook up your own IR serial link with stronger transmitters (or 
buy some off the shelf, non- IrDA) or use fiber optics running through a 
sealed wall?

It's not clear to me what the constraints are in your system.

Regards

Bruce 


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