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Re: 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
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>
>


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