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General BMW Questions
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  #1  
Old 07-15-2016, 07:43 AM
nbruno1108 nbruno1108 is offline
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How does keyless entry work?

New here, not new to BMWs. I've been doing some research on BMW's keyless entry system and I can't for the life of me figure out how it works. How does the car sense the key is in required proximity? What kind of sensors are in the door handle to detect touch to lock and unlock the car?

Can any BMW techs or engineers enlighten me?
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  #2  
Old 07-15-2016, 08:48 AM
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acoste acoste is offline
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Quote:
Originally Posted by nbruno1108 View Post
New here, not new to BMWs. I've been doing some research on BMW's keyless entry system and I can't for the life of me figure out how it works. How does the car sense the key is in required proximity? What kind of sensors are in the door handle to detect touch to lock and unlock the car?

Can any BMW techs or engineers enlighten me?

The key sends a signal every couple of miliseconds. This signal fades in ~100 feet so one antenna in the car can detect the key if it's within that distance. However one antenna can't tell where the key is.

Therefore they put 5 antennas in the car at different locations and the control unit calculates the location of the key based on the signal strength received by the antennas and using triangle method similar to the GPS system.

Door handle has a capacitive sensor on it. (similar to touch screen) The value of a capacitor depends on the permittivity of the dielectric material. When no one is touching the handle, the dielectric material is air. The human body has a different permittivity than air so when someone puts their hand there, the capacitance of the sensor changes. And that's what the car is monitoring.



EDIT: have to make some correction: similarity to GPS on location is a bit vague. The GPS uses signal delay to calculate distance where the comfort access uses signal strength, the triangle principle is the same.
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Last edited by acoste; 07-15-2016 at 08:54 AM.
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  #3  
Old 07-15-2016, 06:46 PM
Rick D Rick D is offline
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All I can add here is it works slick....
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  #4  
Old 07-29-2016, 09:53 AM
jaye944 jaye944 is offline
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to add; the key must be close enough to the sensors usually in your pocket; if a guy is trying to fuel up with key in pocket, you can jump in but not start the car
you can't also lock the cars from outside with the keys inside the car or in the boot (tried it!)
and the key needs to be in a specfic place to start" the car as well (usually with the driver, center console, front door areas wheel wells
you get a warning if it cant detect the key, especially if you've started the car and got out and dropped it,
so you can't "accidentally drive off" with no key, if you do; it wont start again
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  #5  
Old 07-29-2016, 09:54 AM
jaye944 jaye944 is offline
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its called CA - Comfort Access
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  #6  
Old 07-29-2016, 10:24 AM
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Tom K. Tom K. is offline
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Originally Posted by jaye944 View Post
its called CA - Comfort Access
And was originally termed "Convenient Access"

From my '07 manual table of contents:
"Comfort access, refer to Convenient access"

Tom
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  #7  
Old 07-31-2016, 12:55 AM
328iblack 328iblack is offline
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Very interesting, also you can use your head as an antenna. Your brain is 80 percent water and will amplify the signal from your remote. Put your remote on your head and try it. Also works for a cell phone. I can't use all those scientific words, but it's pretty spiffy!!
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Old 07-31-2016, 09:42 AM
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acoste acoste is offline
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Originally Posted by 328iblack View Post
Very interesting, also you can use your head as an antenna. Your brain is 80 percent water and will amplify the signal from your remote. Put your remote on your head and try it. Also works for a cell phone. I can't use all those scientific words, but it's pretty spiffy!!
Amplification won't happen, but reflections. The total power emitted from the antenna spreads in all the direction, 360 degree. Now if your head is in the way, some of the radiation will get reflected on the border where permittivity changes (this case it's the first layer of the skin). Therefore the signal that goes toward the other direction will have the direct and the reflected waves combined increasing the signal strength by 10-20%.
This effect is definitely measurable with instruments. I'm surprised you can experience this in real life.
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Last edited by acoste; 07-31-2016 at 03:42 PM.
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  #9  
Old 07-31-2016, 11:36 AM
328iblack 328iblack is offline
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How does keyless entry work?

I have a powerful head!!! Science is so cool!!
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  #10  
Old 07-31-2016, 02:51 PM
ProRail ProRail is offline
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Originally Posted by 328iblack View Post
I have a powerful head!!! Science is so cool!!
True dat. Would that the world (the US world) agreed.

Last edited by ProRail; 07-31-2016 at 02:53 PM. Reason: clarification
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