Re: Hmevision ir transmitter

["andy_powell_is" <ukha@xxxxxxx>]

Dave,

> The outputs on Homevision are open collector NPN or PNP?

Errrr... chicken soup


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

I believe so...


> 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 

Ermm.. do you mean like this: (if yahoo doesn't screw it up!)

+5v--+---C    E----
          B
     +-R---+
           


R=resistor
C=collector
B=base
E=emitter

Andy


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@b...>
> To: <ukha_d@y...>
> 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@b...>
> > To: <ukha_d@y...>
> > 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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> > >
> > >
> >
> >
> >
> > 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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