This is my first indestructible, I wouldn't have posted this because I always do things like this and I lose site that sometimes they can be cool or useful to others, but a coworker told me I should, so here I am. Also I underestimated the current draw and capabilities of the original design and had to correct it. This gave me the opportunity to take pictures and such for illustration. Before I get started let me say that while this indestructible will tell you how to start your car with a flash drive; this will be a reengineered flash drive and should never be plugged back into a computer or plug an un-engineered one into the car for fear of what might happen. The reason for this indestructible is quite simply I am cheap (new part is $100 and labor is $200) and I love creatively fixing things around the house with junk I have laying about. So the problem is the ignition stopped turning in my car, a '96 BMW 328i (this makes the problem more complex later). I will cover the unique challenges my car represented but also instruct the general techniques needed to adapt this for any vehicle. A side from the three automotive relays (purchased to solve the current draw issue) everything used was found lying around in my junk bins.
My parts list is:
1x Front panel USB plug from an old computer case
1x Old 2GB USB SanDisk Cruzer flash drive (who uses 2GB flash drives these days anyways)
2x automotive relays with two normal open contacts
1x automotive relay with one normal open and one normal closed contact
1x 12v relay with one normal open and one normal closed contact for electronics (had it laying around but could have used another automotive one as well)
Step 1: Remove the vehicles interior panels
The first step is to remove the interior panels in the car to gain access to the wire harness used for the ignition. This varies for every vehicle and is outside the scope of this indestructible. While you are removing the panels take note and plan where you are going to mount your USB plug. I chose to mount it on the lower panel that covers the steering column. Keep in mind that your wire length will also be a limiting factor in your placement. Carefully measure and cut a hole where you wish to mount the plug, keep in mind there needs to be clearance from other parts in the vehicle when you reinstall the panels. You may want to double check multiple times to ensure you have chosen the right placement. A wrong choice will lead to multiple holes in your interior panels which never looks good.
By the way, the interior plastic is very tough to cut so if you chose to do it by hand as I did please be extremely careful not to cut yourself. I used a hobby knife to carefully cut the hole in the plastic, but what you have or choose to use is up to you. I thought about using a Dremel but chose to do it by hand so I had more control and provide a more accurate result.
Step 2: Dismantle the wire harness
Next you have to figure out which color wire does what for the vehicle. You can get a manual from your local auto parts store or you can just figure it out like I did. I removed the wire harness for the ignition and took it inside to my desk. I then carefully (there maybe springs and such inside) took it apart trying not to break it in case I ever want to fix my car the right way. Once I got it apart and located the little steel ball that went flying across my office (did I mention springs and such) I examined the contacts and used a multi-meter and determined the information that I needed, and also found my first curve ball that BMW threw.
Step 3: Create a schematic
The typical ignition has four stages/positions; off, auxiliary, on, and start. In most cars off is off, no power is applied to anything here was the curve ball courtesy of BMW. My car has an anti-theft device that is armed when the key is in the off position. The next position is auxiliary, in this position most power is applied to the radio and 12v power outlets. When the key is in on position everything has power, however the mechanics of the ignition accomplish this by having two contacts, the auxiliary contact and the "on" contact. The key being in the on position completes the circuit for both contacts applying power to auxiliary and everything else. Last is the start position, normally this position takes the "on" position and adds the completion of the starter circuit causing the starter to turn (curve ball two from BMW). In the start position for my BMW the auxiliary contact is released while the starter is engaged (I can only speculate that this limits power drain from the battery while the starter is turning, did I mention I have a German spec BMW). Now that I know what does what I can create my schematic.
Step 4: The fun begins
Now armed with a schematic, parts and junk bin the fun can begin. First grabbed a burned out ATX power supply for wires and carefully pulled a few of the Molex connecters out of their housing (going to use these to attach the completed project to the vehicles stock harness). I then drilled a hole in each terminal on the relays to provide better support for soldering the wires to. I proceeded to solder all the wires to the relays and added a small bit of shrink tube to each terminal after the wire was attached to limit the chances of a short while driving.
Step 5: Soldering the bread board
Next I grabbed a circuit board from an old IDE hard drive and clipped four of the pins off the board and carefully pulled them from the housing. I will use these to solder into my bread board as a plug for the USB front panel wire. Now it's time to solder the last relay, the four IDE pins, and the wires from the other relays to the bread board. Once that was completed I cleaned up the bundle of mess with some electrical tape and moved onto the key (flash drive).
Step 6: Time for the "key"
Carefully take apart the flash drive (no worries here there are no springs in the flash drive). I de-soldered the contacts of the USB drive from the board so I can solder to them and not worry about the circuitry of the flash drive and the unwanted effects they may have on my key. Using a small piece of wire I soldered it across the two inner contacts so that when the drive is simply plugged in it will complete the circuit effectively turning the car on. Next I removed a surface mounted power button from an old laptop and soldered it to the two outside contacts. When the button is pressed it completes the circuit engaging the starter. Due to the fact the circuit board of the flash drive wasn't designed to have a button in the location I wanted, one of the chips needed some modification (broken off with a screwdriver) to allow it to fit and I was forced to superglue the switch into place.
Step 7: Time for the test
Now it is time to head back outside and install my new bundle of wires into the car. I plug in the flash drive and the car and radio turn on, so far so good. Press the hidden button inside the flash drive and wait nothing happened. Well that doesn't make any sense the logic is sound, the schematic is well designed, why doesn't it start. I can hear the relay clicking so I know it is wired right, what gives? Bam hit by another curve ball from BMW. Another anti-theft device, the factory key contains a small RFID chip that must be very close to the ignition for the car to start. Well that isn't cool; the point was to replace the key. So I removed the RFID sensor from around the ignition and took it inside. At my desk, again I carefully pried open the key (again no springs here) and removed the tiny RFID chip, and reassembled the key.
Step 8: The old key
Back to the car to experiment with the placement of the chip in relation to the ignition to find out how close it has to be to still work. This thing needs to be almost right in the ring for it to sense that it is there. Well superglue it is, well maybe not, apparently whatever this thing is made out of won't stick to superglue. So back to the house to rummage the junk bins; there has to be something here I can use to create a nice cover over the ignition and hold this chip in the perfect spot. I couldn't find anything that would look nice, if only I had the 3D printer my wife won't let my get, I could fabricate a very nice cover and you would swear it came from the factory that way. I found things that would work but they turned out to be ugly. I want it to look nice it is a BMW after all, even if it is 17 years old. Well for the time being a small piece of electrical tape will do. I will hit the stores on Monday when they open to see what I can find to replace the tape, even though you can barely tell it's there. I still know it is and that just isn't good enough.
Step 9: Finally Complete
One last test; and she starts, pull the drive and she dies. Finally everything is working as planned, time to put the interior panels back on and take her for a spin.
I hope you enjoyed this indestructible and I welcome any comments and criticism. I look forward to posting more of these as it really drives my wife crazy. Now my small tinkering projects will go from an hour or so to all day events and I steal her camera for the duration.