[s-cars] IR to RF conversion

[Theodore Chen]

> i'd like to convert it to RF, and was looking at the link that bill
> posted some time ago:
> http://www.mnsi.net/~natwhite/Audi/lock.htm
> http://www.mnsi.net/~natwhite/Audi/Images/audialarm.jpg
>
> has anybody here done this conversion?
> i'm also wondering why he used relays for the pin 4 and pin 3 connections.
> i understand he wanted to ensure that positive voltages never got applied
> to the factory alarm inputs (which are expecting a negative voltage), but
> why not use diodes?

i bought the prestige APS-25CH, which is similar to the APS-25KB 
recommended in the above link, but it has code-hopping and double-pulse
unlock capability.  this latter feature is more important, as it enables
you to eliminate one wiring connection and a relay.

instead of simultaneously triggering the unlock wire and disarm wire as
in the above link, my APS-25CH triggers the disarm wire twice by sending
two ground pulses.

the APS-25CH does indeed flip-flop as described in the link.  on its
unlock wire, it will send a ground pulse when you hit unlock, and send
a +12v pulse when you hit lock.  so you need to make sure that the 12v
pulse doesn't get through to the factory wiring.  instead of using relays,
i used diodes.  59 cents a pair from radio shack, and i prefer solid state
to electromechanical devices.

incidentally, the link is misleading in that there is no -12v line.  it's
ground (zero volts).

my alarm has another channel that i was going to use to trigger the
window/sunroof close feature, which i disconnected after my central locking
module started triggering it randomly.  however, the alarm only provides
a short ground pulse.  the window/sunroof closing feature runs only while
it's receiving a ground signal, so a short pulse does nothing.  does
anybody know of a relay with a short timer built in?

-teddy




		
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