Electronics help with IR TX-RX

["Graham Howe" <graham@xxxxxxx>]

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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