I have an E39 with a diamond 433Mhz 3 button key and a simple spare key. My diamond key is after-market of which the case opens as the battery of my original ran out and i got a new case, soldered a new battery in and had the key grinded(?) for € 5.
BMW e39 Keys.jpg
As i am always surfing on ebay and other sites to see if there are new 'upgrades' available for my car I came on to the following conversion case (€10-25, depends where you buy it). It is supposed to convert your diamond key to the newer types of keys however the best thing about this 'new' design is the key actually flips. don't have to worry which pocket my key is in, phone scratches, pointy end, etc
BMW conversion case.jpg
I did not order one but first found several cases on eBay.de (i live in Holland) to see it would really work. I found out it works ONLY if you have a seperate transponder in the Diamond key. Of course in my case the ID44 transponder is soldered to the green circuit board and in that case the new conversion key case would not start the car. If you have a separate transponder in your diamond key you supposedly can just transfer everything. Something like this:
BMW case chip.jpg
Now i was wondering... My simple spare key (which has is worn and cracked) has a separate transponder. The only thing i would need is a key circuit board with 433Mhz to program with my car. (Programming is really easy, many tutorials on the web). After a long search on eBay i found out you can buy a remote circuit board for a BMW diamond key in China for in between €15-25.
If i would buy the circuit board, take out the transponder from my simple spare key, buy a conversion case, assemble all, have the key cut/grinded and initialize the remote circuit board, would it work ? I am inclined to Say it would... Any thoughts on this key case conversion?
i would still have the diamond key and instead of the simple spare key a nice flip key. It would only cost around €25-35