Capacitive door handle waveform

Posting this up for anyone else that might find this interesting. Nothing of huge diagnostic value, just me poking around in systems I don't know about. :silly: A 2013 Lincoln MKT came in with part of the 'Intelligent Access' system inoperative. The what? In English, the system that'll lock and unlock the doors for you if you touch the door handles, as long as you have the key on your person. There are two capacitive sensors in each door handle. One is inside the handle itself to request unlocking, and the other is shaped like a button on the outside of the handle for locking.

The drivers side lock and unlock didn't work, which is what happens when someone leave the door handle connector unplugged the last time they had the door panel off. :lol: But I'm there now, so I decide to get some known good data anyway. Here's the snippet of the Ford wiring diagram for reference:





What I ultimately found was this: The ground is exactly that. The ANT + and - never did anything, zero all the time. The interesting part was the VBATT. Here's what you see on that wire while touching the lock button:





I didn't know what to expect, but it sure wasn't this. :lol: The unlock button generates a very similar signal, only small-big-small-small-big-small. Unplugged, the signal stays at a steady 12ish volts.

My takeaway is that this circuit functions in a very similar way to a Dodge/Chrysler digital wheel speed sensor , with the power feed and signal circuits being the same thing. OEM's love their capacitive touch panels on all kinds of stuff these days, so I'm honestly expecting to see more sensors generate signals like this in the future.

Hmm very interesting ? bI learned my trade inn simpler times,. anybody got a De Lorean or TARDIS I could borrow.?

Andy.MacFadyen wrote: Hmm very interesting ? bI learned my trade inn simpler times,. anybody got a De Lorean or TARDIS I could borrow.?

Right? :lol: But seriously, what was wrong with a normal switch input? Seems like some engineer needed to justify his paycheck.

Pretty cool! I wonder if you could set the scope up to detect changes in the ground side when your finger is near or on the touch area. I'm thinking you would have to set the voltage scale to a point where you also see "noise"

I was just reading about "capacitive touch panels" since you posted this cause I realized I knew nothing about them haha.

I was reading this
www.allaboutcircuits.com/technical-artic...itive-touch-sensing/

graywave wrote: Pretty cool! I wonder if you could set the scope up to detect changes in the ground side when your finger is near or on the touch area. I'm thinking you would have to set the voltage scale to a point where you also see "noise"

You might be right? I regret not being able to spend more time with this system, otherwise I'd be happy to play with it more.

I was just reading about "capacitive touch panels" since you posted this cause I realized I knew nothing about them haha.

I was reading this
www.allaboutcircuits.com/technical-artic...itive-touch-sensing/

YES. Good stuff.

I mean, it's useless in the day-to-day diagnostics, but that doesn't mean it's not interesting! :silly: