Re: Hmevision ir transmitter

["andy_powell_is" <ukha@xxxxxxx>]

<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
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
> 




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