Re: Simple RF/IR distribution

[Williams Christopher C <CCWILLIAMS@xxxxxxx>]

I think I was being naive in thinking that you could just amplify and
re-transmit all the noise including any IR signals present and let the
filter/demodulator in the receiving equipment do all the work!  I guess
you would have problems with the signal levels and swamping the IR
signal with the noise.

I have just had a look at the Maplin circuit on the recommended web
site.  As far as I can see it does not have a 38-40kHz oscillator in the
transmitter.  Am I right in assuming that the signal conditioning IC
used (TBA2800) does not demodulate the signal?

Does anyone know how to alter this circuit to work with multiple
receivers?  I guess it would be OK as long as the power supply can
handle all the receivers and if the extra standby current doesn't mask
the current fluctuations used to transmit the data.   The problem is how
to bypass the distribution amp!  I suppose you need to decouple the DC
at the input and output connections with 100p ceramic capacitors and use
an inductor to link the source with the destination (dc only).  Am I on
the right track?

Cheers,

Chris Williams

> -----Original Message-----
> From:	Nigel Orr [SMTP:nigel.orr@xxxxxxx]
> Sent:	Wednesday, March 01, 2000 11:57 AM
> To:	ukha_d@xxxxxxx
> Subject:	[ukha_d] Re: Simple RF/IR distribution
>
> At 11:39 01/03/00 -0000, you wrote:
> >> If you did this in the analoge domain, it would work for any
type
> of IR.
> >
> >Any circuits please...?  Open to all suggestions (except CAT5 -
I'm
> not
> >doing that in this house, next one..... probably)
>
> I'm not sure what is being suggested, but I'll try to explain the
> usual
> system.  An IR receiver usually consists of a tuned circuit, set
> between 36
> and 40kHz, with a _lot_ of AGC (gain control) and filtering to get rid
> of
> extraneous noise.  The output of the tuned circuit is a digital pulse
> train.  Typically if you use a receiver in the 38-40kHz range, it will
> decode every IR remote's codes, with probably a slightly reduced range
> (but
> still enough for domestic use) at the frequency extremes.
>
> The digital control signal is then used to trigger an oscillator at
> 36-40kHz to drive an IR LED.  Again, frequency isn't too critical
> unless
> you need long ranges.
>
> The digital signal can be transmitted any way you want- down the phone
> line, over cat-5, over an RF link, some other wired modulation scheme,
> you
> could even use X10 if you weren't in a hurry!
>
> What you don't want is to receive and repeat all the noise that is
> received
> by an IR-sensitive photodiode- just the desired signal.
>
> Now, which analogue domain did you have in mind? :-)
>
> Nigel
>
>
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