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'IR data transfer'
1998\10\26@222214 by Dennie Lee

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Does anyone out there know of any schematics/code to do relatively high
speed IR data transfer?  I am looking for a method of relatively short
range wireless data transfer, but RF modem are out of the question (at
least for right now due to budget concerns.)  If no one has any code or
schematics, does anyone at least know what the maximum theoretical data
transfer rate of the Radio Shack IR emitters and detectors is.  I read in
the Piclist archives about someone using the Sharp 40khz IR modules and
transferring data at 2400 baud, I may end up using that.  Any
comments/suggestions?


-- Dennie Lee --
spam_OUTdwlee1TakeThisOuTspambbtel.com                ICQ: 19351768
http://www.uofl.edu/~dwlee001  <- Being Rebuilt

1998\10\26@233152 by Mark Willis

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Some electronics surplus site has laptop IR transceiver cubes for $2
each or something, you can get way over 2400 baud with those.  If noone
knows what site, I can go through bookmarks & find 'em <G>

 Mark, .....mwillisKILLspamspam@spam@nwlink.com

Dennie Lee wrote:
{Quote hidden}

1998\10\26@235520 by Gabriel Gonzalez

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I am really interested in these!!!

Please, go find the bookmark!

Calvin

-----Original Message-----
From: Mark Willis <.....mwillisKILLspamspam.....NWLINK.COM>
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Date: Monday, October 26, 1998 10:30 PM
Subject: Re: IR data transfer


{Quote hidden}

1998\10\27@064216 by Mark Willis

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Done, http://www.goldmine-elec.com/pag9229.htm, Part # G9229
$2.00   * 10/$18.00  * 100/$175.00  * 1000/$1500.00.

 (Even got the price right <G>)

 Mark, RemoveMEmwillisTakeThisOuTspamnwlink.com

Gabriel Gonzalez wrote:
>
> I am really interested in these!!!
>
> Please, go find the bookmark!
>
> Calvin
>
> {Original Message removed}

1998\10\27@064219 by William Chops Westfield

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   Some electronics surplus site has laptop IR transceiver cubes for $2
   each or something, you can get way over 2400 baud with those.  If noone
   knows what site, I can go through bookmarks & find 'em <G>

Electronics goldmine.  http://www.goldmine-elec.com/

These are (apparently) IRDA transceivers, which means 1) they should be good
to 115200bps, 2) over short range (< 1 meter?), 3) need to be driven with
appropriately modified async waveforms.

BillW

1998\10\27@211136 by J Nagy

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Dennie Lee wrote:

>Does anyone out there know of any schematics/code to do relatively high
>speed IR data transfer?  I am looking for a method of relatively short
>range wireless data transfer, but RF modem are out of the question (at
>least for right now due to budget concerns.)  If no one has any code or
>schematics, does anyone at least know what the maximum theoretical data
>transfer rate of the Radio Shack IR emitters and detectors is.  I read in
>the Piclist archives about someone using the Sharp 40khz IR modules and
>transferring data at 2400 baud, I may end up using that.  Any
>comments/suggestions?

       Personally, I wouldn't use these modules at 2400baud. Let me explain...
       I sell a couple of PIC based infrared receivers that use these
modules on the front end. They respond fairly well to Sony infrared signals
(the default mode for most 'all-in-one' infrared transmitters). The format
for one bit consists of ~0.4ms of no carrier, followed by about 0.8ms('0')
or 1.4ms('1') of carrier. Bit times are thus on the order of 1ms, giving
about a 1kbps transfer rate.
       From what I saw in my testing (agc type delays, noise due to nearby
lights, etc), I would possibly push to twice this rate (your 2400) at the
max, but would expect quite a few errors, and would certainly not go any
higher. My choice would be 1200, if the application permits. If you go
higher, please share your results with us.

       Jim

       Elm Electronics
Makers of unique integrated circuits
http://www.elmelectronics.com/


'IR data transfer'
1999\01\19@151129 by John Payson
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>Does anyone out there know of any schematics/code to do relatively high
>speed IR data transfer?  I am looking for a method of relatively short
>range wireless data transfer, but RF modem are out of the question (at
>least for right now due to budget concerns.)  If no one has any code or
>schematics, does anyone at least know what the maximum theoretical data
>transfer rate of the Radio Shack IR emitters and detectors is.  I read in
>the Piclist archives about someone using the Sharp 40khz IR modules and
>transferring data at 2400 baud, I may end up using that.  Any
>comments/suggestions?

|        Personally, I wouldn't use these modules at 2400baud. Let me explain...
|        I sell a couple of PIC based infrared receivers that use these
|modules on the front end. They respond fairly well to Sony infrared signals
|(the default mode for most 'all-in-one' infrared transmitters). The format
|for one bit consists of ~0.4ms of no carrier, followed by about 0.8ms('0')
|or 1.4ms('1') of carrier. Bit times are thus on the order of 1ms, giving
|about a 1kbps transfer rate.

>From what I can tell, the normal IR receivers are totally unsuited
to the handling of 'straight' async communications since they have
a very wide margin between the shortest and longest times without
any data transitions.  Instead, I'd suggest using something like an
interleaved 3-of-6 code:

Every six on/off cycles encodes a byte (or if you want to push things,
one of 400 states).  Three of the on pulses are longer than the other
three pulses, and three of the gaps are longer than the other three
gaps.  To receive the data, store the lengths of the received pulses
and gaps, and look for the longest three of each.

Although the interleaved 3-of-6 approach requires sending more pulses
than direct async communication, its reduced requirements for precise
pulse lengths would allow the pulse rate to be increased without aff-
ecting reliability.  It would remain to be seen, of course, just how
far the technique could be pushed, but it should be reasonably effect-
ive.

1999\01\20@102820 by robert a. moeser

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John Payson <spamBeGonesupercatspamBeGonespamCIRCAD.COM> wrote

>I'd suggest using something like an interleaved 3-of-6 code:
>
>Every six on/off cycles encodes a byte (or if you want to push things,
>one of 400 states).  Three of the on pulses are longer than the other
>three pulses, and three of the gaps are longer than the other three
>gaps.  To receive the data, store the lengths of the received pulses
>and gaps, and look for the longest three of each.

i was going to write for some details but i figured it out. the
nice thing is, as pointed out, that precise pulse lengths are
not so critical.

identify the numbers of the 2 longest "on" pulses. there are 20
different combinations of the 2 items selected out of the 6 pulses. fastest
decodong would be a table lookup i am betting.

same thing goes for the gaps.

so 20 different "on" decodes and 20 different "off" decodes represents
400 different states.

but... unless the bytes are coming steadily, there are really only 5
gaps... and picking 2 or 3 longest can only identify 10 different
combinations, giving only 200 codes. not quite a bit short.

and if the bytes are coming packed in time, how do we tell where one
starts and the other ends?

so maybe for IR data transfer use interleaved 3-of-7?

-- rob

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