Active RFID "convenience entry" and "keyless ign"

 

The goals are to minimize what is carried and maximize real world convenience. Therefore, if I have to press a button, I may as well fish out a car remote. If I have to activate any additional switches than normal, I may as well use a car key. In short, whatever I have to do MUST IMPROVE the convenience factor over a standard vehicle. Otherwise, it's no good.

 

The product found and used is a combination piece. It is an RFID and standard RF code hopping keyless entry. The idea is this: the RFID enables the RF signal to be sent. Even if the RFID is spoofed, the car will not activate in any way because the codehop signal is not sent. The codehop signal is sent every 2 seconds at long range but is not translated by the unit until the active RFID is sensed as in range.

 

The effective range is approximately 2 meters. This changes drastically of course with antenna position, orientation, and proximity to metal (especially between tags). The CnF used ONE antenna which was OK at best. The tag had to be fairly close to the car to work. This problem was solved by moving the antenna to the exterior of the car, just next to the drivers side door handle. This fixed all the range problems, but only when approaching the driver's door. This covered me for 95% of car use, but not if I approach the tailgate only, or a passenger side door.

 

The solution was to expand the system to a five antenna system, which I finished construction this evening.

 

Five antennas feed all their data into a main control module (based off an Atmega microcontroller) which interprets incoming signals from the RFID and also the main system alarm. This prevents door operation from happening if the doors are previously unlocked from the standard alarm fob. This also prevents door lock operation from RFID signals getting picked up or dropped all over the place, which is VERY likely to happen in an environment like a car.

 

I suppose I should mention the safety systems in place, such as disabling the RFID into the "on" state when the accessory line is on to prevent door lock operation when the car is moving, etc.

 

So without further ado! Here is how the whole system essentially behaves:

 

1. If any of the five antennas are sensed, door unlocking is enabled.

2. Door unlocking is enabled using a shock sensor sensitive enough to sense knocking on any part of the car, such as a window. This was NOT a part of the CnF product and may be bypassed. The CnF design unlocked the car when in range, which meant the car would unlock then lock if I simply walked by to get to my wife's car. The shock sensor also allows me to avoid running additional wiring into every door for capacitive touch sensors

3. Three antennas placed at the exterior of the car ensure the car can be approached fro many direction and allow access. The antenna locations are one to each side by the doors and one behind the rear bumper to enable the tailgate.

4. Door unlocking is done via remote keyfob inside the car. Traditionally, this method is a waste of time because OEM alarms can be disabled electronically, usually by pulsing a particular wire with ground. However, this method was chosen to ensure an aftermarket keyless entry/remote starter remained in sync with the factory alarm and doorlock positions at all time. This behavior is absolutely dictated by the system controller.

5. The additional two antenna are located inside the cabin and serve no purpose (for now) other than to bypass the factory RFID transponder. This is accomplished using an RFID key located in the center console of the car electronically tied to the ignition switch.

 

The center console location was chosen to allow my access to the key as a backup method to start the car. None of my designs are relied upon for sole control of the car and are typically augmented by at LEAST two backups, preferably three. The key is kept safe by placing it inside a lockbox used by realtors to store house keys. Any theft could not result in a stolen car.

 

The use of the wireless keyfob allows the control of a secondary device. In particular, a garage door opener similar to a homelink system. This allows for the removal of additional clutter in the car since a traditional remote garage door opener is no longer required.

 

The tag itself is stored in my wallet in the form of a flatpacked PCA placed next to the coin battery. The thickest device is the status LED retained as a visual confirmation the RFID is operational (it blinks every time the RFID and RF signal are sent), allowing for placement into a credit card slot of the wallet. The tag bypass switch is removed to prevent accidental activation under conditions such as sitting on the wallet. Testing so far has shown the PCA itself resilient to damage by this stimulus.

 

The whole contraption inside the car is stored where a factory amp once lay, under a passenger seat, protected from any outside influence from a rear passenger foot or any other wandering appendages.

 

Here is a shot of the device after RFID programming, well after system controller programming.

 

 

It's clear this is an alpha. The five system boards are seen stacked as tightly as possible, with the system controller located at the upper right next to the keyless fob. Main power comes in from the bottom left as do the status inputs and outputs. Bottom center is the shock sensor set REALLY REALLY sensitive to allow the slightest vibration to unlock the doors when the wallet tag is sensed in range. I am hoping this design choice is not premature, that it is ready for prime time.

 

The total cost for this is all quite cheap. The RFIDs are K9 sombras from eBay at a cost of $35 a pop including two tags. The Atmegas if overpaying are just above $10 a pop. The keyfob is not required and only used in this case to enable remote starting. The transponder bypass is not needed either and only used to enable the separate installation of a keyless ignition. This is done by epoxying a keycopy to a knob and leaving it in the ignition after disabling keysense. This prevents thieves from recognizing a key in the ignition as many modern cars now have knobs where the ignition switch used to be (nissan versa, nearly every mazda since 2007, selected BMW and mercedes) but allow the whole assembly to start the car. Of course only when the fob is sensed inside the car by the two internal RFID antenna.

 

Thanks for looking at my bloody mess of wiring.

 

The shock sensor was a failure. For some reason, car alarms go off left and right at 3AM when a cat sniffs the paint, but I couldn't mount the sensor solidly enough and set it sensitive enough to operate in a "classy" way. Meaning at least as convenient as MBZ or BMW convenience entry cars.

 

So I rewrote the software to CnF operation, which is simple. Sense in range, unlock the doors. period. It works, and much better now with five antennas in the system. No instabilities yet.

 

I did just re-place every antenna in the car. So the alpha needs a few months to see if the placement is workable. Still some operation delays on the passenger side of the car and I'm not sure I have the rear antenna placed far back enough yet (it is just "in the trunk", not "behind the rear bumper", so sensitivity might be lower than I'd like)

 

I'll have to take a shot of it installed in the car. It is located where the OEM stereo amplifier was, so it's protected from passenger feet and sticky hands.

 

all in all, I am very happy to have a system in place. I took out the CnF product several months ago and it was just inconvenient to operate the car!