Re: Another IR Success !

[Nigel Orr <nigel@xxxxxxx>]

At 12:35 13/11/00 +0000, you wrote:
>I managed to get most of the items except the zenners and IR LED.

For a 1-off (where saving pennies isn't a problem), any 5V1 zener and any
IR LED should do (though Graham had trouble with one of the Maplin LED
types, and another worked fine- I'm not yet sure why- it could just be that
some of them are particularly sensitive to being connected backwards- try
with a large series resistor (1k?) first or use a multimeter with a diode
test and/or compare it with a known visible LED)

>the transmitter needs to actually point towards the kit your trying to
>control, but other than that it worked very well.

Transmitters are usually quite narrow beamwidth, there is a lens in front
of the LED 'chip' to focus the light so there is more power over a narrow
angle.

>* Every now and then I notice that the transmitter LEDs flash by
themselves,
>this was at night, is this normal?

Yes, but if you can find out why you might be able to avoid it.  The TSOP
circuitry copes very well with noise sources, but if you connect the output
to a 'scope and turn on a nearby fluorescent light, there's a burst of
noise from it until it 'readjusts'.

The resulting burst of IR shouldn't ever false-trigger anything, but it
will stop you using the IR distribution while the LED is flashing on its
own.  Is the receiver positioned where passing car headlights etc could be
visible?  In the daytime, the constant sunlight is easy to cope with, but
flashing lights are harder to ignore!

It _could_ be interference being picked up by the cable- if you remove the
cable and connect a 10k or bigger resistor at the transmitter end, does it
still happen?  What if you reconnect the cable but not the TSOP
receiver?  If it only happens occasionally, it's probably fine, but it's
probably fixable if it's a nuisance...

>* If I have the Receiver module near the transmitter module I get some
sort
>of feedback, where by the transmitter stays on.  Are there ways round
this?

I can't think of one, except by physical positioning of the transmitter and
receiver.  You could have a more 'intelligent' system with central
switching, so you don't send IR to a room where you have just received it
from.  That wouldn't be very difficult (could be handled by simple logic
gates), but would take a bit of designing.

Easiest answer is probably to use low power to the IR LEDs (try bigger
series resistors) and position them very close to the equipment.  Then put
the receiver far away from that, eg in the opposite corner of the room.

>* I want to replace the batterie supply with a transformer of some
kind.  Is
>it Ok to use one of the DC Transformers that Maplin sell for arround a
>tenner.  Should I get a 'Regulated' one?

Just about anything from 9V-15V should be fine.  The 555 isn't too fussy
about supplies, and you already regulate the supply to the receivers, so
unregulated should do fine (mine is unregulated, the same one that's
powering a couple of CCTV cameras).

>* I'm thinking of housing the transmitter circuit at a distance from
the
>actual LED's.  How long can cables joining the circuit to the LEDs
actually
>be.  A few people have suggested I position the IR transmitters on the
>actual kit.  Anyone got any ideas about this?

Mine is on the board, and will probably get fixed to the back of a
loudspeaker or stand, which is close to, and in front of, the A/V
stuff.  The cable length isn't really a problem (this is a far from cutting
edge circuit, you can get away with a lot of changes without upsetting
it!).  You might find LED output drops off a bit down a long cat5 cable,
especially if you are using the transistor and 100 ohm resistor setup, if
it does you can just measure the resistance and decrease the series
resistor accordingly.

I'd also suggest you don't share the cable to the LED with anything
else.  The 'signal' cable between receivers and transmitters (lower
frequency, and much lower current) is much less likely to cause
interference, but it's probably best kept away from audio/video if you can
avoid it- could be shared with burglar alarm contacts etc.

So, for all practical purposes, cable length from the 555 to the LED
probably doesn't matter.  As I posted before, keep the series resistor on
the board, so if you happen to short out the cables it's less likely to
damage anything else.

>* If I want more that one reciever, where do I join them.  I have three
>cables between the receiver and transmitter currently with +12v, Signal
and
>Ground.

The only common connection you need for all transmitters and receivers is
Signal and ground.  Each could have their own supply.  That's why it's easy
to add additional transmitters and receivers, the receivers half-heartedly
pull their output high when inactive, so any one receiver can override the
others when it 'sees' a burst of IR.  If it was the other way round, it
would be more important that each was on the same supply voltage etc etc.

>   Do I just add more TSOP's with the zenner and diode to drop the
>voltage down to 5v each time.

Yes.  Alternatively, you could have one centralised 5V supply, and feed
that to all the TSOPs (they only draw a couple of mA each), and a 12V
supply for the transmitters- that would make the receivers even
smaller.  My receivers will probably all be mounted in PIRs where there is
already a 12V supply.  The transmitters will run off the 'auxiliary' supply
I have connected to Comfort.

>   Also If I want more transmitters can I just
>add extra IR LED's or should I build several transmitter circuits.

Either, if your transmitter locations are nearby, just use parallel LEDs,
if they are far away, put another transmitter on the signal/ground 'bus' at
any point (with the right polarity!!).

>build more than one transmitter circuit can I just join them on the
same
>bus.

I'm planning to, and it was designed with that in mind.  I'll probably have
10 receivers and 2 transmitters when I'm finished (2010 maybe?), but I've
not tested multiple units yet.

Nigel


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