RE: Electronics help with IR TX-RX

["Keith Doxey" <ukha.diyha@xxxxxxx>]

Hi Graham,

I dont have the receiver circuit to hand but the TX  should be fine on
13.8.

The 555 timer used in the receiver has a supply range of 5-15V

The receiver failure is also strange. The TSOP1838 has a supply rating or
3-6V but keep it to 5 for safety. If I remember the circuit correctly there
is a dropper resistor between the 12v supply and the +ve input of the TSOP.
There should also be a 5V1 Zener diode at the input of the TSOP to clamp
the
voltage to 5.1V.

It sounds as if you have made a mistake with the voltage dropper circuit
and
are running the TSOP above its rated voltage. It is probably struggling
with
12v and failing completely at 13.8.

Keith

BTW I do still have TSOP1838's at £1-50 each.

> -----Original Message-----
> From: Graham Howe [mailto:graham@xxxxxxx]
> Sent: 15 May 2001 19:20
> To: UKHA List (E-mail)
> Subject: [ukha_d] Electronics help with IR TX-RX
>
>
> As many of you know, I eventually managed to put together some working
IR
> transmitters and receivers with help from several on the list and
> despite my
> non-existent electronics knowledge. However I now have a problem, the
kit
> works fine when I use a 12V battery and connect both TX and RX to it
(with
> an additional wire between them for the signal). I am currently in the
> process of installing Comfort and so drilled a little hole in one of
the
> PIRs and inserted an IR RX unit. I connected the 12V and 0V from
> the PIR to
> the unit and used a spare wire in the CAT5 cable for the signal. Then
I
> connected up the TX unit via Krone blocks and patch panel and it
didn't
> work. After I finished cursing myself for not testing the set up
before
> gluing the RX inside the PIR I started to investigate. After much
probing
> with a voltmeter, I discovered that the 12V output from Comfort
> was actually
> 13.8V and that when fed with this voltage the kit wouldn't work,
> in fact the
> TS1308 (is that the right code? If not it is the things Keith was
selling)
> seemed to die after a while at this voltage (I now have 2 dead
> ones). I then
> tried having just the RX unit fed by Comfort and the TX fed by
> the battery,
> this didn't work either, even though I could see the 0.5V drop in the
> trigger wire when IR was received. At this point I started thinking
that I
> was well and truly out of my depth, so I started guessing what might
be
> wrong. Here are my thoughts:
>
> The RX unit will operate correctly for at least a limited time when
> connected to the 13.8V, the trigger wire shows 5V which drops to 4.5V
when
> IR is received.
>
> The TX unit does not appear to like the higher voltage at all and
> certainly
> doesn't react correctly to the trigger when the higher voltage is
applied
> (could it be that the 0.5V drop is no longer sufficient to do the
'magic'.
>
> Both a RX and a TX unit appear to have been killed during my
experiments,
> possibly as a result of the high voltage.
>
> It seems I have two options, either use an alternative power
> supply that is
> closer to 12V and therefore put up with less convenient wiring inside
my
> PIRs. Or use some sort of electronic trickery (possibly a resistor?)
to
> reduce the voltage supplied from Comfort (after all the Comfort
> outputs are
> labeled 12V).
>
> Please can one of you electronic geniuses give me some advice,
> with the DDAR
> price increase this is turning out to be a very unsuccessful day!
>
> Graham
>
>
>
>
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>
>




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