RE: Urgent - Time to kill, want to build IR Extender

[Nigel Orr <nigel@xxxxxxx>]

At 16:14 02/11/00 +0000, you wrote:
>though I think I'll wait for Build 2 of your open source schematic.

Thanks to those who have kept me up to date on progress, I will try to
incorporate solutions to their problems, ideas for testing etc in the next
version, along with more detail on the receivers.  The page that's there
was more aimed at seasoned electronics folk, but I realise there are people
who want to build it, but have little electronics experience, so I need to
be a bit clearer on some of it!

>I lost thinks a little here, what is the TSOP.  I would like to start
off
>with a single receiver and a single transmitter to test things out.

That's about as far as I've got so far :-)  The TSOP1838 is a superb IR
receiver, it's about the size of an LED and includes a photodiode, filters,
amps, automatic gain control and a demodulator.  Basically, you connect 2
of the pins to a 5V supply, and the third pin goes 'half-heartedly-high'***
when there's no IR present, and low when it sees IR.  That's the really
complex bit, as it has to cope with all sorts of different strengths of IR
and external interference.  My circuit does the really simple bit- when the
input goes low, it flashes an IR LED at 38kHz, when it goes high, it stops.

*** By this, I mean it doesn't try really hard to produce 5V, it just
connects the output via a big resistor to 5V.  Because of that, if there's
another device in parallel (for example in another room), and it receives
IR and tries to pull its output to 0V, all the other receivers will let it
do that quite happily.

Nigel


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