RE: IRDA Repeater

["Ian B" <Ian@xxxxxxx>]

Hi Keith

I have been learning a bit about the IRDA format and have learnt the
following.

The IRDA protocol is as you say  short range one but in addition to this it
is also a low power one in the computer world. This means the time to
transmit 1 bit value 1 would be x. With IRDA this value is only sent as a 1
for say 1/4 x and the remaining time there is no transmission. This cuts
down on power consumption but makes decoding and retransmitting it a little
more of a challenge. More information for those interested at
http://dbserv.maxim-ic.com/appnotes.cfm?appnote_number=631

Quite how all this relates to remotes I am not sure.

Ian (still saving for a descent scope)

p.s. Keith, any recommendations for a scope within a mortals price range?

> -----Original Message-----
> From: Keith Doxey [mailto:ukha@xxxxxxx]
> Sent: 29 November 2001 22:33
> To: UKHA Discussion
> Subject: [ukha_d] IRDA Repeater
>
>
> Hi All,
>
> Been doing some experimenting with the IRDA bits that I ordered and
have
> found a few things out.
>
> Please note... all findings are based on observing the digital
> output on an
> oscilloscope as I dont have any IRDA kit to test with other than an
NTL
> remote.
>
> IRDA does not use a carrier signal unlike normal IR which tends to use
a
> carrier or 38-40 kHz.
>
> IRDA receivers will output a clean signal from any type of remote. An
NTL
> remote that gave a very weak signal using an IR photodiode gave
distinct
> pulses that had the full 5V swing. (A TSOP1838 totally ignores the NTL
> Remote). Using a normal Digibox remote gave an output that clearly
showed
> the bursts of 38kHz carrier. Each of the individual pulses could be
seen.
>
> I believe that if the output pulses of the IRDA receiver were
> used to drive
> an unmodulated IR LED then the output would faithfully follow the
input
> signal both for IRDA and Normal remotes. I still need to try this
> to confirm
> if this is the case.
>
> So far so good.....but....
>
> the downside :-(
>
> IRDA is designed for short range communication only. Despite the
powerful
> output of a Remote Control, at 2 metres the reception was decidedly
dodgy.
> Moving only slightly off axis lost the signal totally. By
> comparison, using
> a TSOP1838 for the Digibox remote I could point it anywhere I
> wanted and the
> signal would bounce around and get picked up reliably.
>
> What might help is if I could find out what receiver module is used
within
> the NTL boxes as it can obviously receive over quite a wide angle and
from
> normal domestic viewing distances. Anyone volunteering to peek
> inside their
> cable box to see what it uses ???
>
> I experimented to see if it was possible to put both receivers in
parallel
> so that the TSOP would override the IRDA receiver when using a
> normal remote
> but the results were less than good. The output from a normal
> remote using a
> TSOP looks something like this
> _________         ___________         __________         __________
>
> Using an IRDA Receiver it is like this
> - - - - -         - - - - - -         - - - - - -        - - - - - -
> The combination of the two gave an output like this
> _ _ __________       _ _ _________       _ _ _________     _ _
__________
>
> which would severely corrupt the signal.
>
> I think that it would be possible to produce an IRDA repeater but I
dont
> think the range would be as good as with a normal IR repeater. At the
> moment, it is not looking good for producing a repeater that will
handle
> IRDA AND Normal 38kHz Modulated IR. It could be that KAT5 will include
> normal IR repeating functions but a secondary system would be needed
to
> handle IRDA.
>
> I know Ian is wanting to get IRDA working for his design and a dual
system
> can built into a single enclosure. Ian only uses 3 or 4 of the wires
in a
> cable so has spare conductors to carry the additional signal for
> IRDA. Once
> I have got a bit more info I will pass it onto him so he can look
> at adding
> IRDA to his units.
>
> Here endeth the latest chapter on IRDA.
>
> Keith
>
>
>
>
> For more information: http://www.automatedhome.co.uk
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