Re: Re: Hmevision ir transmitter

["Dave McLaughlin" <dave@xxxxxxx>]

Andy,

I don't have Homevision so please help out here first,

The outputs on Homevision are open collector NPN or PNP?

Do they sink current to ground when the output is ON?

If my assumption is that the output goes to GROUND when on, then you
will
need to put a pull up resistor on the output to +5V to make the output go
to
HIGH (almost +5V but not quite) when the output is OFF. This will of
course
mean that you will have an inverted version of what you expect and may
need
inverting again.

Hope this helps
Dave...

----- Original Message -----
From: "Frank Mc Alinden" <armagh@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Friday, May 31, 2002 1:13 PM
Subject: Re: [ukha_d] Re: Hmevision ir transmitter


> Andy
>         The best person to
explain these things is off list at the moment
> K.D. When you supply a small current to the base emitter this allows
a
much
> larger
> current to flow between the collector and emitter,depending on the
gain of
> the transistor. You are using the transistor basically as a
switch,
> switching it on and off rapidly to mimic the ir signal.
> The ground signal i think you are referring to is supplied by the
open
> collector output of HomeVision .When someone refers to open collector
it
> means that the collector is connected to ground when the ouput is
active.
>
> Andy  hope this makes sense also i hope to teach myself 
Visual Basic as i
> want to learn a high level language so i will have lots of question s
to
ask
> you programmer gurus
>
> Frank Mc
> ----- Original Message -----
> From: "andy_powell_is" <ukha@xxxxxxx>
> To: <ukha_d@xxxxxxx>
> Sent: Friday, May 31, 2002 9:55 PM
> Subject: [ukha_d] Re: Hmevision ir transmitter
>
>
> >
> > <meep><meep>
> >
> > Just as an addition to my earlier message, I'm actually starting
to
> > understand why I am having problems understanding what is going
on,
> > having done that I think I understand what we are doing, but
still
> > have some questions... So I'll explain what I understand, then
ask
> > the questions...
> >
> > 1. For a transistor to work there must to some +ve voltage going
into
> > the base connector, we use a high resistance value betwen the
base
> > connection and the +ve voltage to reduce the current flow, and
hence
> > the current drawn is minimal..
> >
> > 2. When a +ve voltage is applied to the base then current will
flow
> > from the collector to the emitter. No current will flow 'back up
the
> > base' because it has a high resistance value, and "current
takes the
> > path of least resistance" (IIRC my basic physics..)
> >
> > 3. when we have the two transistors, when a +ve voltage is passed
to
> > the base it allows current to flow from the collector to the
emitter
> > on TR1. The emitter on TR1 is connected to the base of TR2. The
base
> > of TR2 now has a +ve voltage and so will allow current to pass
from
> > the collector to the emitter on TR2. So when TR1 'comes on', so
does
> > TR2.
> >
> > Thats what I understand...what I don't understand is :
> >
> > 1. If the base of TR1 needs a +ve voltage, and we need a +ve
voltage
> > on the collector of TR1, where is the ground? Don't we have to
have a
> > +ve and ground for current to flow?
> >
> > 2. On a breadboard we can just link to the same +ve supply
(there's
> > still the "where's the ground" issue), but when it
comes to
> > Homevision, what then? The IR jack supplies the +5v, and the A
ports
> > (Port A1 to A8) provides the ground.. but then the base wont have
a
> > +ve volatage will it? So nothing will flow between the collector
and
> > emitter of TR1, and thus TR2 will do nothing..
> >
> > I'm beginning to understand much more than I did at first, 99%
has
> > been theory, unfortunately the 1% practical hasn't worked so
far... :(
> >
> > Andy
> >
> >
> >
> > --- In ukha_d@y..., "andy_powell_is" <ukha@b...>
wrote:
> > >
> > > Ian,
> > >
> > > I had a very quick look this morning, tried the short but
nothing
> > > happened. I'll have a proper look tonight when I get home,
and I'll
> > > also take a photo and upload it to my site so you can see
the
> > > mess^H^H^H^H circuit I did...
> > >
> > > Andy
> > >
> >
> >
> >
> >
> > For more information: http://www.automatedhome.co.uk
> > Post message: ukha_d@xxxxxxx
> > Subscribe:  ukha_d-subscribe@xxxxxxx
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> > List owner:  ukha_d-owner@xxxxxxx
> >
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http://docs.yahoo.com/info/terms/
> >
> >
>
>
>
> For more information: http://www.automatedhome.co.uk
> Post message: ukha_d@xxxxxxx
> Subscribe:  ukha_d-subscribe@xxxxxxx
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>
>



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