RE: Re: ir transmitter some success

["Ian B" <Ian@xxxxxxx>]

Baby, baby, baby, 30 seconds mail, baby, baby - you get the
picture.........
;-)

Transistors are amplifiers which means that you can switch a large
current
with a VERY small one. I cannot remember which circuit you are using
but
here is a guess. In order for a transistor base to work it needs a
circuit.
The fact that it switches the collector is almost incidental in this
case.
Maybe the emitter is connected to the base of the other transistor
(thereby
completing the circuit) and the current flow is enough to trigger the
base
of the second tranny into switching its own collector. Transistors are
also
proportional at very low base currents. If you apply a very small current
to
the base the transistor will only allow a small amount across the other
pins. You can demonstrate this with your LED circuit and apply the
voltage
to the base of the transistor through ever larger resistors. At some
point
the LED will start to dim as the flow is slowed.

I hope this explains a few 'features' of electronics.

Ian B

>-----Original Message-----
>From: andy_powell_is [mailto:ukha@xxxxxxx]
>Sent: 02 June 2002 12:18
>To: ukha_d@xxxxxxx
>Subject: [ukha_d] Re: ir transmitter some success
>
>
>
>Frank Ian, Ian,
>
>I've actually found a problem :(
>
>When +5v is applied to the base of the first transistor, even if
the
>collector is not connected, the 2nd transistor is supplying current
>to the LEDs... I don't understand that. didn't think it should
>happen :(
>
>any ideas
>
>Andy
>
>
>--- In ukha_d@y..., "Frank Mc Alinden" <armagh@b...>
wrote:
>> Hi Andy
>>            
Isnt it  brill when things go right .Your doing great.
>Good idea
>> about the Basic Stamp. I spent all day yesterday frustrated .
You
>wouldnt
>> learn much if everything went right ,its when it goes wrong
thats
>when you
>> learn. Did you post your photos on Marks Website ? if so how?
>> Good Luck
>>
>> Frank Mc
>> ----- Original Message -----
>> From: "andy_powell_is" <ukha@b...>
>> To: <ukha_d@y...>
>> Sent: Sunday, June 02, 2002 7:18 PM
>> Subject: [ukha_d] Re: ir transmitter some success
>>
>>
>> > Good stuff Frank... at the moment I am just using this to
learn,
>in
>> > the end I'll probably end up using one of the designs from
you
>> > experts...
>> >
>> > I've had a little brainwave here too... before connecting
to
>> > Homevision I'm actually going to sacrifice a basic stamp..
(well
>> > sacfrifice is'tn the right word as it SHOULD be ok
afterwards)..
>> >
>> > The Basic stamp can cope with 30ma max per pin and 60ma per
8
>pins..
>> > which means if i create a fake homevision using the basic
stamp I
>can
>> > certainly check on the current draw before the final
connection..
>> >
>> > Obviously this is the final test before connecting to
homevision..
>> > before all that I need to take some measurements.... but I
have
>> > transferred the first bit from  breadboard to
stripboard... :D :D
>> >
>> > and it works!! :D .. I'm just using this one really as
>layout...and
>> > testing, I need to compress  it really...
>> >
>> > I also think I have got it down to about 512ma total of 8 X
9
>leds, i
>> > think by chance I managed to get some sensitive ir emitter
leds I
>> > need to double check but I think I can get away with
600ohm
>(possibly
>> > more as the emitters will be right beside the internal IR
>receiver of
>> > any kit) resistors for them and the visible leds have
3.9k
>resistors
>> > and are still fairly bright... (again all by chance)
>> >
>> > Part numbers for farnell are:
>> >
>> > 178301 Ir Emitter
>> >
>> > (farnell datasheet http://www.farnell.com/datasheets/5344.pdf
)
>> >
>> > 3013900 yellow led
>> >
>> > (no datasheet at farnell but it is at www.marl.co.uk 
marl part no
>> > 352-582-20 )
>> >
>> > Andy
>> >
>> >
>> > --- In ukha_d@y..., "Frank Mc Alinden"
<armagh@b...> wrote:
>> > > Hi Andy , Ian + Ian
>> >
>                            
Had some success today with the 8
>zone
>> > ir controller . I decided to bypass the opto connected to
>incoming ir
>> > signal from Hv to confirm my suspicions. Tried it again and
it
>worked
>> > but only with two ir leds inserted in the Zone Splitter .
Looked
>at
>> > my schematic and realised it was slightly different to my
homebrew
>> > circuit. In my homebrew unit the driver transistors were
connected
>> > common emitter but my new circuit was common collector .Re
did the
>> > driver transistors and tried again. Now works with all 8 ir
leds
>in
>> > Zone Splitter on all Zones . The range is approx 15ft and
i
>monitored
>> > the current which was approx  5mA . I set up my Hv ports
thru the
>> > control menu rather than a macro at this stage just to
confirm my
>> > hardware was connected ok. Would still like to use opto
isolation
>on
>> > the incoming ir ,will order something from rs components. Now
must
>> > update my drawing before i forget.
>> > >
>> > > Frank Mc
>> >
>> >
>> >
>> > 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
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>

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