RE: cables, sockets and plugs, whole house audio, x10 DI N modules

[Nigel Orr <Nigel.Orr@xxxxxxx>]

At 04:49 10/08/00 -0400, you wrote:
>Nigel, this is *exactly* what I've been trying to achieve.  I built a
>prototype circuit based on a CA3140 opamp, (see
>http://www.mitedu.freeserve.co.uk/Circuits/Interface/irext.htm
)

I'd seen that one, I'd honestly be surprised if anyone could get it to
work.  Biggest 'missing bit', unless I'm missing something, is that there's
no AGC (automatic gain control) for the signal.

The approach I've taken sends the demodulated signal, and 'assumes' 38kHz
modulation frequency at each end.  The receivers are incredibly simple,
consisting of a 5V regulator, a smoothing capacitor, and one of the 'all in
one' IR receivers from Temic (via Maplin).  They include AGC, amplfier and
demodulator, and even a pullup resistor, so you put 5V on the supply and
out pops demodulated signal on the signal pin.

Particularly impressively, I switched on a fluorescent desk lamp, about
20cm above the receiver.  The output flickered for a second or so while the
AGC adjusted, but it still coped with a remote about 2m away once it had
settled.  I've tried the prototype at home, a few metres from a compact
fluorescent (CFL and similar tend to cause the most interference), and
easily got 6m range (it's hard to get further on a line-of-sight in the
house), so it should be fine for any room.  It didn't work well with the
TV, but I'll investigate that more some time...

The transmitter is based on the ubiquitous NE555 timer (cos I've got a pile
of them, and there are lots of pre-designed IR circuits around so I didn't
even have to think!), driving an IR LED through a transistor, with an
inverter on the input so it links with the active-low signal from the
transmitters.

> the visible indicator led seems to pulse/flicker (as expected),

Do you have a 'scope?  If not, try varying distances from remote to photo
diode and photo-diode to equipment- it's possible something is getting too
low or too high a signal.

If it's not too difficult to swallow your pride, I'd recommend the
demodulated route though... it should work much better over longer
distances, and the reception bit is traditionally quite tricky to design
from scratch- a complete receiver is definitely easier.

>equipment doesn't respond :(  Also, even though I'm using a SFH2030
with a
>builtin filter, it still seems to pick up non-remote IR...

Sadly not surprising...

>Any chance of a circuit diagram etc.?

Absolutely- I've done most of the schematic using Eagle (nice freeware
version available from http://www.cadsoft.de for Linux and
Windows, BTW!),
you can have it as that or a .GIF, what format would you like?  I'll
probably not do a PCB as it's such a simple circuit and I only need a
couple of them, just build it on tri-pad breadboard (it's currently on the
plug-in prototype board)

>BTW like the idea of housing the receivers in the PIRs

I was quite pleased with that too... if it's easy, I'll mount them
internally, but I'll probably just drill a 5mm hole and stick the receiver
through the front.  Advantages and disadvantages of it being mounted
internally are:
+  Not visible, better blocking of daylight
- PIR lens will give patchy coverage,

All in all, externally is probably better

>the old adage rings true - you will always find a use for spare cables
that
>you had doubts about at installation time!

Absolutely... and usually a couple of pairs extra that you thought would
just be completely OTT...

Nigel


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