RE: Re: Electronics Gurus brain required...

["Ian B" <Ian@xxxxxxx>]

Spot on Andy. The tranny TR1 only needs to be small as there is no
current
flow. TR2 however takes the full flow from up to x number of emitters
so
needs to be suitably sized. It also needs to switch at a rate suitable
for
IR transmission.

All this switching on and off of current can set up a resonating effect
which is undesirable for circuit operation. A decoupling cap acts like
a
battery and when there is a demand it helps the power supply by
discharging
some of its stored energy. When there is no demand it charges up again.
Ideally it should be calculated with charge and discharge rate
associated
with the IR but his is more knowledge than I have currently. I work on
the
'copy other circuits' principal and pinch another's ideas and values. I
guess you could have lots o small caps at each diode take off or one
near
the power supply that is larger. Trial and error here is good as long
as
they are connected up correctly.

For testing purposes I would build the circuit up from the IR end back
towards HV testing each bit worked. If not you may end up with a non
working
circuit and not the foggiest where it is going wrong.

Hope this is helpful

Ian B

p.s. Babs arrived so my time is a little short at the moment and I am
knackered!! Mum and daughter doing well, no names decided on yet.

-----Original Message-----
From: andy_powell_is [mailto:ukha@xxxxxxx]
Sent: 28 May 2002 14:14
To: ukha_d@xxxxxxx
Subject: [ukha_d] Re: Electronics Gurus brain required...


--- In ukha_d@y..., "i.bird@t..." <Ian@M...> wrote:

> *********************HOW TO*************************
> Basically and without thinking it through too much you would have
> HV power from the jack running to the collector (the in) of a
transistor.
> The emitter (the out) from said transistor would run to to base of
another transistor (resistors would be needed).
> The first tranny would be switched by PORTA somehow. This gives
the
zoning. Can't remember how PORTA works so I cannot say more now.
>
> All you need then is a power supply through the IR LEDs to the
collector (the in) of the second transistor
> As above this is being switched by the 'zoning' transistor.
> Connect the emitter to ground and off you go. Again resistors may
be needed to stop the LEDs going pop.
> ******************END HOW TO**********************

Ian following your message I did a search for transistors, to try and
get some understanding of what you mean.. I think I got the general
gist...(you can see it here:

http://groups.yahoo.com/group/ukha_d/files/Transistor.bmp

Am I going along the right lines? I'm making some assumptions:

I would need 1 x TR and 1 x TR2 for each Homevision port used (ie the
diagram above is an 8th of what the circuit might look like...

You'll explain what a "decoupling capacitor" is, and where it
should
go...and what it does?

Andy






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