Re: Nigel's IR transmitter - some questions from a beginner about to bu ild one.

[Nigel Orr <nigel@xxxxxxx>]

At 11:00 13/11/00 +0000, you wrote:
>1) How big is the finished product?, and I presume that the IR LED can
>be separated from the rest of the module (by a length of cable).

It depends how big you make it.  I'd say about 1" x 1" for the
circuit
board if you make the effort to think about it and solder all the external
connections, 2" x 2" easily, with IDC or screw terminals.  If you
used
surface mount components, or built in onto the back of a DIL socket, it
would probably be about a 1cm cube.  You could then pot it in epoxy, if you
want something truly small!  The latter approach isn't recommended for the
inexperienced!

The LED can be separated, someone asked if they could use the 'stickon' IR
emitters, if I had one I'd know, but I presume they are just an IR LED and
a series resistor or something, so should be fine?  If the LED is near the
equipment (<1m), and the equipment isn't in direct sunlight, you can
probably dispense with the 2nd transistor, and just replace the visible LED
with an IR one, driven from the 555 output.

If you are just connecting the LED down the cable, put only the LED at the
end of the cable, keep the resistor on the board, that makes it less likely
that you'll damage anything if the LED legs or other wires short out, and
won't affect the performance at all.

> going to have to be in a very visible location to have clear line of
>sight to all of my AV equipment,

Most receivers have about a 60 degree cone of visibility, and you might
even be able to bounce the IR off a wall or something, have a play and see
what works.  Bear in mind that sometimes things that reflect visible light,
eg mirrors, don't reflect IR well, and vice versa.

>2) Can I put a device on the serial port (or any other port for that
>matter) of a PC running HomeSeer to feed IR commands to the same
>transmitter?  How can I build/buy such a device?

Possibly... what does homeseer provide (I don't use it)?  If it can already
produce IR, at worst you can put a TSOP1838 directly in front of the IR
LED.  At best, find a point in the circuit where there is demodulated IR
and interface that to the other devices.  I'd need more details to be able
to help.  I think some of these systems produce the demodulated data
directly on the serial port, so it would interface easily, but I'm not
sure.

The only other snag is that you might have problems from connecting a
serial port Ground connection into the system at one point, with another
mains earth at another point, but if you use a 'wall wart' adaptor with an
isolated earth it might be OK.  I've not tried it.

>Nigel and Keith must be getting really worried, with all these
>beginners getting their soldering irons out!  :-)

Definitely not worried, I'd be delighted if it got more folk interested in
designing electronics.  I just hope it's not too frustrating for beginners
to build something that wasn't really well designed to be a 'project'
kit.  I'm happy to try and help, but it's maybe not a good 'first kit', I
know how frustrating it can be to try to get something working!

It's _very_ encouraging to hear from those like Graham H who have kept
going and tried things until it worked.  I learnt electronics initially by
breaking kits, by misassembling them, then understanding what was wrong,
and how to fix it, and moved on to fixing things that had been broken in
some other way, and then designing stuff for myself, and trying to avoid
all the other designers errors.  I wouldn't have learnt anything if I'd
always followed accurate instructions to the letter (except how to solder)

I suspect that folk who build it on plugboard and have a play around with
different things might get 'hooked', those who go straight to solder might
find it less interesting, particularly if it doesn't work first time.  But
either approach is fine!

And I'm sure Keith will be happy to know lots of experienced electronic
assemblers when he sets up his 'sweat shop' to go into mass production of
KAT5 systems :-)

Nigel


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