So I finally reopened my Audi FOB to fix the problem with the wiring. It seems that two of the switches were shorting, causing a constant battery drain and keeping the current low enough to not allow signal transmission. At least this was the best answer i could come up with. The funny thing is that it was not due to my wiring or soldering. The short was cause because two of the three similar switches use the terminals differently than the third, conducting across two lengthwise posts, rather than two widthwise posts.

I took the pictures on top of my solder bench, because it thought it would yield good contrast. I did not realize my camera would pick up the solder burns and metal fragments with quite such detail...

Here are the major shell components for the Audi fob.


This is the two board folded and ready to be put in the Audi shell. You can see where I cut the Audi circuit board in order to make room for the wires. I made sure to leave material on the ends of the board so it would still lock into place inside the Audi shell. If either side had been removed, the panic button would not find enough pressure against it to activate the button (it was stiffer than the others and mounted horizontally, not vertically.)


Here is the boards unfolded and with the tape removed.


This shows where I had to carve the Audi shell in order to fit the security chip, and the height of the extra circuit board inside the Audi case (infiniti board in addition to audi board.)


Heres a general overview of the two circuit boards. Battery leads needed to be much larger than the original, due to the new battery placement. I soldered on some strips I cut from an old XBox360 controller I had hacked apart a year ago. You can see that the wires are snaking around a good deal. It was impossible to determine the exact length of each wire solder time, so they were bent into positions that would let the entire assembly fit in the shell (just barely).


Heres a pic of the antenna. I'm using stranded copper wire (22 gauge I think) and I measured the length by laying it on top of the original antenna before i cut the infiniti circuit board.

 

hey good job. how's it working for you?

 

Good and bad I suppose. I must still have a short on the trunk switch, because it acts as though it is intermittently held down. The other three buttons act like they are supposed to, and I was able to program the remote to interact with the car.

I'm pretty pleased with the results, and I should only have to crack the FOB one more time to fix everything (I hope.) Other than the nicer look, I love the fact that my keys are now held farther away from the dash, so they don't make noise but hitting the dash during turns or bumpy roads. This mod was probably worth it solely for this benefit.

 

I'll give ya $30 for it...

prally not? right... GREAT work though!

 

Turns out I didn't need to crack the case again. Not quite sure how, but it seems to be working completely.
I am quite pleased with the results. It looks classy enough to match my coupe, still has a 20+ foot range, and dropped a lot of mass from my key chain.
I recommend this conversion as a nice diversion if you have a little experience with a soldering iron or are crafty in general.

 

Since i ended up cracking my FOB again, for the first time in several months, i figured i would give an update.

Over the last many months, the range on my fob has been slowly going down hill. At first it though it was due to an intermittent short, so i would replace the battery more frequently, but it would only buy me a little of my overall distance back each time. After this last replacement, where i noticed almost no gain, I came to the conclusion it is due my my antenna, and that i had been throwing away relatively good batteries.

I had made my antenna out of several stripped and twisted strands of copper wire pulled from a spare ethernet cable (20 gauge i think), which over the last several months has been oxidizing. My reception problems were due to the initial length of the antenna (which despite my best efforts turned out arbitrary) and this oxidation of the wire surface.

I bought some "Magnetic wire" at radio shack today for around $7 to form a new antenna. I assume this is intended to create electromagnetic spools for motors and such, there by creating large impedance which might adversely effect the fobs performance, but i am pleased to say that this has not been a problem (at least not with the lengths I am using.) My though was to craft a new antenna using a Koch showflake fractal. As in cellphones, and our antennaless cars, they are designed to work on broader frequency ranges than a standard strait wire antenna. The other key was to match the initial length as closely to the fob frequency as possible.

Using This length calculator and our frequency of 315mhz, i needed a total length of 17.83 inches for an ideal antenna. Here is the Koch snowflake pattern (its pretty recognizable:

The problem is that every step only reduces the overall size by 25%, so i would need 8+ steps to fit it within the FOB. After a few tests i could see that this was not practical. So instead I opted for an non-overlapping series of bends.

Obviously, the real thing has many, many more bends and is much more closely spaced, but the distance between each bend is length of one of the sides of the correctly sized Koch snowflake (i think it was something like 0.554 inches per leg.) After much bending and positioning, i ended up with my new antenna.

In the end, after re-assembling my FOB all the responses are much faster and more "crisp" than they ever were with my first homemade antenna. The responses seem equal to, if not faster than my stock FOB, however this might just be my imagination. I have not had a chance to test out the full range of the signal, but compared to yesterday at 5 feet, i can now trigger responses at 30 feet though a concrete block wall.

Overall, this seem successful

 

hah f*ck that , i aint messing with my remote , looks complicated, but porps

 

so did you use the factory battery or just the mazda one? accordfreak?