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2Addicts | BMW 2-Series forum Technical Topics DIY and Coding Discussions How exactly does the Start button work?

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      10-28-2014, 04:05 PM   #1
cw128
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How exactly does the Start button work?

I'm wondering if anyone knows exactly how the Start/Stop button works in the M235i... I have a slightly crazy idea about replacing it with something else that I can control from a microcontroller (perhaps a fingerprint reader hooked up to a Raspberry Pi). Yes I know it is a stupid idea but humour me

So I'm just wondering if it is simply a case of when you press the Start button it closes a relay to make up a circuit (in which case I can easily tap in to that) or if it is a lot more complex than that? I'm not sure if it is standard but I have the "keyless go" option where you just need the key to be somewhere close to the car and then the Start/Stop button will work, so I'm assuming there is no actual security required behind the button itself and my microcontroller closing a relay would have the exact same effect as pressing the original button would have (assuming I had taken the button out) ... but that seems to easy to be true.

In reality I'll probably never have the balls to actually try and implement this but it would be nice to know if it is possible

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Chris
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      10-28-2014, 04:56 PM   #2
zipphreak
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The transponder in the key still has to communicate with the ECU and handshake the security protocol. The start button is merely there to send a digital request (over CANbus network) to the computer to control the starter/ignition/accessory wires I assume. Ever notice when you get near the car with the key there are some relay noises, whereas I assume it is the computer engaging the fuel pump.

Check this out..

http://hackaday.com/2012/07/07/keyle...easy-to-steal/
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