Using implant with factory keyless open and start

I got myself a car with keyless entry and pushbutton start. But carrying a fob is so 2010. Actually I’m really worried I’m going to lose it. It falls out of my pocket so easily.

The idea is

  • use an RFID access controller and build an interface between it and the fob
  • The interface controller will control the power to the fob as well as the lock/unlock.
  • A fob will need to be dedicated to it and be left installed in the car somewhere

Challenges:

  • The car senses when the (powered) fob is in the car making it difficult to lock the doors
  • The car knows when the fob is inside the car and disables the pushbuttons on the handle. Makes sense or locking your doors to keep people out while you are inside would be impossible. But it’s a consideration when the fob will be permanently in the car.

I used:

  • DT xAC (v1) EM access Controller
  • Seeeduino XIAO Arduino compatible microcontroller board
  • 3.3v voltage regulator
  • NPN Transistors (x3)
  • 10k resistors (x7)
  • Assorted wire, breadboard, headers and connectors

Logic:

  • On powerup, unit is at idle and goes to sleep waiting for an interrupt on the input from the access controller. Note the access controller is always powered up.
  • On a valid scan detect from the access controller, it powers up the key fob, it waits 500ms and unlocks the door (simulates pressing unlock button)
  • A countdown timer is started for 30 seconds. If you do not start the car in 30 seconds, the car doors lock, the fob turns off, and the the controller goes back to idle/sleep mode.
  • If the car is started, the ignition input goes high which puts it into a “driving” state that just keeps the fob powered up. It ignores any RFID scans.
  • Once the car is turned off, the countdown timer is again started. After 30 seconds, the car locks, the fob is powered down, and the controller goes to idle/sleep mode.
  • If a scan is detected during the countdown mode, the countdown is immediately completed, doors are locked and the controller goes to idle/sleep mode.
  • If the car is turned on while in idle/sleep mode (like a second key is being used), nothing happens. The fob stays powered down as to not interfere with anything and door locks are not activated.

I think it will work well.

I had to disable the “Left keys in the car” warning otherwise the horn beeps three times every time you close the door.

I haven’t installed it yet as I want to install it in a secure location which is not near where I want to put the antenna. So I am going to attempt to extend the RG-174 coax using SMA connectors. Hopefully I won’t lose too much range.

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Properly Extending the xAC (v1) antenna

Note that SMA connectors come in two flavors, regular, and “RP” for reverse pin. Standard SMA have a pin on the connector with the internal threads and a socket on the side with external threads. RP is the opposite. RP and non RP SMAs are not compatible with each other (they can actually damage each other). So make sure you get all the same type.

I purchased a 10ft SMA RG-174 “wifi extension” from amazon. This has regular SMAs.
https://amzn.to/31P7Cvp

Also got some male SMA crimps.
https://amzn.to/30HseWU

I opened the access controller and desoldered the coax. (red and clear insulation)

I cut off the stripped part of the wire and installed a male SMA. Note you will need a proper crimper to install them correctly. (.042" die for the pin, and .137" for the barrel) So now the antenna has a male SMA on it. You can connect it to the female side of the extension cable.

I cut off the male end of the extension cable and soldered it to the board like it was. Take the shield, twist it together and cover in heat shrink (red in the picture above) and strip the center conductor about the same length. Once soldered back, try out your extended antenna.

I noticed maybe a slight reduction in range, but still over 1". And 10 feet is a lot of coax. Shorter distances will have even less range reduction.

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@turbo2ltr your hardware work is always so clean and tidy :slight_smile:

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Hah, it took me twice as long to put that simple board together than it took for me to write and debug the code.

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hah I never said expedient… but quality takes time, and I appreciate quality.

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That’s why we like you @amal. Quality

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Got it installed.

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Didn’t realize the edit option times out. Was going to add this to the top post.

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Just did it for you (bottom of your first post) let me know if you want it moved

Great, thanks!