DIY Mk 4 Switchblade Keyfob Remote using aftermarket alarm keyfob circuit board.

**Cybersombosis** · 12-11-2005 06:47 PM

Well since no one has submitted an aftermarket alarm to MK 4 switchblade remote circuit board swap, I thought I’d post one after completing the final steps last night. This DIY is for a Black Widow 2 button remote. I am sure that all these generic 2 button remotes are very similar and the procedure would be very similar. Most fobs are approximately the same size so I am assuming that if you are going to attempt this, you will have something similar to the size of my fob in the pictures to follow.

The tools that you will need to work with are
- razor knife
- soldering pen (15-25 watts)
- some sort of small vise to hold the piece your working on(I used my fly fishing, fly tying vise)
- wire (I used cat 5 ethernet cable. Small gauge solid copper wire that is color coded)
- small chisel
- multimeter
- electrician’s tape
- extra LED’s. Surface mount LED’s are small enough to fit in the space required. On the original Mk 4 keyfob there is a surface mount red LED that will fit nicely (assuming you have the same keyfob that I got off of eBay). I broke the contacts on my original one so I ordered 5 red and 5 green from my local electronics store.

Here is what I had to work with.

First things first. If you are going to attempt this, make sure you have the aftermarket alarm keyfob programmed. On my first attempt, I used an extra fob I had lying around and didn’t remember to program it. From the first cut I didn’t know if it still worked or not. On the second fob I realized that programming it prior to cutting the circuit board was a must. I essentially used my first fob as a mock up making sure the cut pieces fit the interior of the fob space wise. The second attempt had me running back and forth from my work desk and the car making sure that the fob worked with every new cut and solder. I highly recommend that you take it very slow and make sure your remote works after every cut and solder. Otherwise you are flying blind. Also I stuffed a sock in the aftermarket alarm’s siren so that you could hardly hear the chirp chirp when arming and disarming the alarm constantly throughout this process.

The biggest challenge was getting that big battery into the small space. I had to work around the things that I could not change. I tried to use the 3 volt button battery but the alarm fob decided not to work after hooking it up to the terminals. At first I thought that I would never be able to fit all of the guts of the aftermarket keyfob into the Mk 4 fob but after gutting the interior of the fob of any extra tid bits. I had more room to work with. I took my soldering iron and melted away space for the battery and circuit board then took a chisel and razor knife to cut any of the melted plastic that was still in the way.

You will constantly have to make more room for the components so don’t do any extra work that you don’t need to. Just cut away the obvious things that are sticking out like the circuit board plastic pins and the battery housing for now.

On to the circuit board. Here is a picture of the prospective cuts I will need to do.

After making the first cut on the bottom, I soldered solid wire to the chip fingers that lead down to the circuit to save space. To attach the leads that led from the back and front of the circuit board, I scraped the green circuit board coating coving the copper traces and then prepared the surface and wire you are adding with a touch of flux. The key here is to get some solder onto the tip of your pen first so that you are not waiting for the surfaces to heat up when you have your pen touching the components. Damage can occur if too much heat is applied to the delicate components. Essentially I just tapped the parts I wanted to be attached with the soldering pen and let them fuse together.

Here is a picture of the original cut circuit board. Please note that with the second attempt, the first cut was made and then attached to the remaining three quaters of the circuit board and not as shown as the second cut half way up the board.

With the first cut, I left everything in tact including the battery terminals so that it was easy to test the unit. I clipped the terminals off at the last moment for final fitament. Now for the test.

A point of note, when you have the bare circuit board and are attempting to test the fob, make sure you are not touching the circuit board with your bare hands. I found that a lot of the initial tests worked sometimes and sometimes not depending on how I was holding the bare fob. I am assuming the circuits were either grounding or shorting out on my oily hands or something to that effect. I just held the keyfob in my shirt while testing and that seemed to work fine.

I pushed button 1 and it armed/disarmed, then on to button number 2 and the same. Test completed. Now if you find that you are not getting the results you would if the original circuit board was in tact then back track to all the circuits and make sure you got them all. On the initial cut I had to make 8 connections (16 solders). Make sure the fob is working properly before you move on to the next step. It’s impossible to trouble shoot these little things unless you have some sophisticated equipment which I am sure most of us don’t have. After cutting the first fob, I was left wondering what the hell? I had to move onto the second fob because I didn’t know where to begin. I cannot stress enough about testing the fob at every step. Don’t skip it cause you will regret it and give up on the project (Positive reinforcement!!! Sort of like dogs and treats; humans and chirp chirps).

After making the second cut, I used longer wires to attach the bottom half to the top half. I would eventually replace the third quarter of the circuit board with buttons and remove the third quarter all together. Attach all the leads of the first half of the circuit board to the leads of the second half.