R56 MINI Cooper Auto Sport Button Mod Rev 1.0

I’ve finally hit 1.0! Recently I’ve started to finish up some of my projects that I never completely polished off, and this is one of them! My first stab at putting together this circuit was documented in a previous post here.

This time around, I went ahead and simulated the circuit before fabricating the circuit boards and such. Below you can find the simulation circuit, and the accompanying graphs. It’s important to note that I added an additional resistor between the shottky diode and the capacitor (50kΩ in the image below). This resistor limits the current flowing into the capacitor and causes the MOSFET to be delayed in turning on. This is needed on some MINIs because the ECU in some cars may take longer than others to begin looking for an input from the sport button, sort of like trying to type in your password when your computer hasn’t booted up completely. In the final design I’ve added a 10k ~ 100k potentiometer in order to allow for adjustment, but 50kΩ seems to work well for the cars I’ve tested.

The blue, red, and green probes below correspond to the same color plots in the graph below. We see that once the car is turned on (U2 switches on) the shottky diode (D2) breaks down around 5.1V and C1 begins to charge. The MOSFET turns begins to turn on and, once the threshold voltage is reached, begins to conduct current. For simulation purposes, I’ve added a 10MΩ resistor and 1VDC source to the circuit in order to see the change in voltage as the MOSFET turns on. On the actual circuit, one side of the MOSFET will be held at a potential, and the other will be tied tied to ground.

Simulation_Circuit Simulation_GraphsOnce the simulation was vetted out, I put the circuit together in EagleCAD and got a layout in place, DRC’d, and fabricated using OSH Park. The actual hardware schematic, board, etc. can be found linked below. Here’s what everything looks like in Eagle and after putting it together!

schematic layout

You can see that the circuit is slightly different from the simulation above. I’ve added the potentiometer (R4) instead of a fixed resistor and I’ve also added a switch between the output connector and the MOSFET in order to allow the user to enable/disable the circuit. The board dimensions can be dramatically reduced by removing the switch, if needed.

Below is a picture of the back of the circuit. I chose 0805 pitch resistors and capacitors in order to save space, but I may put together a through-hole version of the circuit if people want to put this together at home.

2013-07-11 19.11.08I hope this helps you put your own Auto Sport Button mod together! If you would like to buy a board (or if you’re local and would like to buy a circuit from me directly), shoot me an e-mail and let me know!

Click the link below to download the files! These files are licensed under a Creative Commons Attribution Share-Alike license. Please remember to credit me for the design if you decide to use them! I only ask that you keep the attribution on the PCB and schematic as-is!