RE: Re: Hmevision ir transmitter

["Ian B" <Ian@xxxxxxx>]

Your circuit looks like I had in mind back in year dot. I have sat down
and
had a think about this and we have been leading you up the garden path
a
bit. Fun trip though wasn't it. Anyway, here are my thoughts..........

I have attached (for my sins) a very small pdf with the circuit (not
quite)
as I saw it in my minds eye.  Things have changed a bit and the TR1
codes
etc. no longer refer to the same transistors so pay attention. After
some
(considerable) thought I figure the best way to do this is use Port C
in
OUTPUT mode. According to the specs it can drive TTL and CMOS. This
means
LED's so enough current for us.

In off state PortC must be all zeros and we don't care what the IR out
is
doing. In this state TR2 is not conducting so the LED's are never on.

Right, from the left ($^%!) we have a pull up resistor connecting to a
tranny TR1. When HV transmits IR the base is pulled low and the tranny
stops
conducting. I assume here that HV switches the ground. This in turn
sends
the voltage through TR2 high. This is where the clever zoning bit is.
If
PortC pin x is high it drives the tranny TR2 base and the voltage
reaches
TR3 - zone ON. If however the PortC pin x was low the voltage would
never
reach TR3 and nothing happens. As soon as the voltage reaches TR3 it
conducts and the LED's come on! Voila...... Obviously the LED's on the
right
would be as many as you want i.e. 8 in your case.

Well, that's the theory anyway.

There may be a better way round this but it is late and I am tired
(excuses
excuses).

I hope this is helpful and that I have got it somewhere near correct.

Off for a midnight snack, have fun. Let me know if the diagram and text
are
rubbish.

Ian B

p.s. you owe me one for making me think!! ;-))

>-----Original Message-----
>From: andy_powell_is [mailto:ukha@xxxxxxx]
>Sent: 31 May 2002 20:25
>To: ukha_d@xxxxxxx
>Subject: [ukha_d] Re: Hmevision ir transmitter
>
>
>
>Ok, I'll try again.... (this is an abridged version!)
>
>I've got the original circuit working.. it was the 2N2222 that
was..
>err dead.. replaced it and it's all ok now...
>
>The circuit now consists of the diagram at
>http://www.automated.it/homevision/HVIR2.jpg
but with the bit that
>says Homevision port removed...
>
>
>> I think I've read the relevant messages. IF I've read them
right
>
>There was a sudden rush of them, mainly due to my lack of
>intelligence :P
>
>> port a o/p is via a PNP which means it will source the o/p and
give
>a +volts
>> supply.
>
>I've used the phrase before, and I'm going to use it again, err,
>chicken soup...
>
>> This lunch I built up a simple circuit details are here:
>> http://galeforce9.dnsalias.org/dsc0_0064.jpg
>
>Thanks, I've saved them for reference...
>
>> You only need the one transistor. It is ZTX651 I had on the
bench
>at work.
>
>Awwww, I have a big bag of 2N2222's and BC182's :(
>
>
>> It will handling up to 2A and does not require any form of
>heatsink. It is
>
>I've put a 1k resistor in from the power supply to the collector of
>the first transistor and according to the Circuit maker I'm pulling
>2.995ma (the 1k resistor appears to drop the current from 32.5ma to
>2.995ma, apparently)... is that a problem? am I going to upset
>homevision by putting that resistor in there? it still works on the
>breadboard...
>
>Bearing in mind that this is only 1/8 of the circuit, if I add 7
more
>am I going to pull too much current?
>
>> an e-line transistor and has a very low on resistance. It will
only
>take
>> about 1mA of current to drive it from homevision. If the led's
you
>use are
>> 20mA devices then each transistor will drive 100 of them. If
this
>is OTT
>
>Phoaaaarrrrr!! 8 zones of 100 emitters :P
>
>> The circuit is wired just to show it working ie the 10K resistor
to
>the base
>> is connected to the 5V rail to simulate a 5v o/p from HV.
>
>So the HV port A supplies +5v too?? This is the bit I'm really
unsure
>of... should I connect the base of the first emitter to Homevisions
A
>ports via a 10k resistor (one for each A port ie one for A1, one
for
>A2..etc)?
>
>
>> If you drop me your address Andy I'll stick it in the post and
you
>can
>> experiment with it. (It is no good to me !)
>
>I'll email it privately... :D
>
>
>>
>> In answer to an earlier question you are correct that for
current
>to flow it
>> needs to complete a circuit. When voltage is applied to the base
of
>a
>> transistor it flows through the base emitter junction of the
>transistor to
>> ground.
>
>You've lost me with this. Where is this? is it that it flows (in
the
>circuit at the url above) to the second transistor via it's emitter
>and off to the seond and then to the emitter of that and hence to
>ground?
>
>
>> I hope I've explained things ok, I'm not the best teacher, but
if
>you are
>> unsure just ask.
>
>You're doing pretty well if you ask me...
>
>> Again so as not to offend the list if ANYONE wants this topic
off
>list just
>> say and it will be.
>
>I did ask and the suggestion was that quite a few people are
>interested, not only that but that this was one of the few on topic
>threads... :O
>
>Thanks for all your help
>
>
>Andy
>
>
>
>For more information: http://www.automatedhome.co.uk
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>

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HVIR.pdf