NFC Central Locking/Ignition
Posted: Thu Jun 23, 2016 5:14 pm
Thought I'd start a thread for this just to keep it a little documented.
The idea is to be completely keyless and to only have to carry an NFC ring or even a card in your wallet.
Started this project a couple of years ago and have had it running on my bike for the past year.
I've had the door locks working in the FTO for the past year as well, but not hooked up because having the reader on constantly drains too much power and would eventually drain the battery.
I have since figured out a way to only have the reader turn on when you put your hand up to it. And that is by using a capacitive touch sensor.
I have made a larger conductor out of a piece of copper board.
I was worried that it would interfere with the NFC signal as anything metal does. But I have made it small enough to not interfere with the antenna.
The only downside to this is it causes a 1.2sec delay. From when you put your hand to it to when it unlocks/locks the doors.
In the video it's running off an arduino so the time is a little longer as it takes longer to boot, but using just the chip on its own is faster.
The lights on the left indicate it's powered up and the light on the right indicates the door is locked/unlocked.
The reader sits in the drivers side quarter window.
It takes an input from the switch in the central locking actuator to know if the car is locked or unlocked and does the opposite.
When it unlocks the car it also flips a latching relay which turns on the reader for the ignition. The latching relay will stay in its position even if it loses the signal power, which it will as the circuit is only on when your hand is near it. The relay flips off again when the doors are locked.
The ignition circuit is a lot more complicated.
So first let me go through the steps of which it operates.
The FIRST tap with an NFC tag turns on accessory. If you open a door at this point the beeper will warn you that it's on, just like leaving your key in the acc position.
A SECOND tap turns on the ignition.
A THIRD tap brings it back to accessory. Now if you open the door here everything will shut off. Let's call this state retained accessory power (RAP)
Now whenever it's in the RAP state, if you tap it will bring it back to ON and keep cycling back and forth.
While in the ON position if you put your foot on the brake and then tap, it will start cranking the engine until it either starts the car or you tap again to go back to the ON position.
When it gets an input from an RPM switch that activates once the car is running above a certain RPM, it stops cranking and we are now in the running state.
At this point tapping will do nothing. So there are no accidental taps and you don't turn the car off at speed.
To turn the car off you need to pull the handbrake up at which point you can tap and it brings you to the RAP state where accessories stay on until you exit the vehicle.
Here is a video that might be easier to understand if you didn't understand some of that.
There are also some mechanical safety features built into the circuit.
The acc and ignition are also on latching relays, so if for some reason power to the chip is lost while the engine is running it won't shut the car down.
If power to the chip is lost when the engine is running it will automatically reset itself to the running state.
I will also be making another reader for the boot release. So you just hold your hand at the bumper and it pops the boot.
I will keep this thread updated as I progress.
The idea is to be completely keyless and to only have to carry an NFC ring or even a card in your wallet.
Started this project a couple of years ago and have had it running on my bike for the past year.
I've had the door locks working in the FTO for the past year as well, but not hooked up because having the reader on constantly drains too much power and would eventually drain the battery.
I have since figured out a way to only have the reader turn on when you put your hand up to it. And that is by using a capacitive touch sensor.
I have made a larger conductor out of a piece of copper board.
I was worried that it would interfere with the NFC signal as anything metal does. But I have made it small enough to not interfere with the antenna.
The only downside to this is it causes a 1.2sec delay. From when you put your hand to it to when it unlocks/locks the doors.
In the video it's running off an arduino so the time is a little longer as it takes longer to boot, but using just the chip on its own is faster.
The lights on the left indicate it's powered up and the light on the right indicates the door is locked/unlocked.
The reader sits in the drivers side quarter window.
It takes an input from the switch in the central locking actuator to know if the car is locked or unlocked and does the opposite.
When it unlocks the car it also flips a latching relay which turns on the reader for the ignition. The latching relay will stay in its position even if it loses the signal power, which it will as the circuit is only on when your hand is near it. The relay flips off again when the doors are locked.
The ignition circuit is a lot more complicated.
So first let me go through the steps of which it operates.
The FIRST tap with an NFC tag turns on accessory. If you open a door at this point the beeper will warn you that it's on, just like leaving your key in the acc position.
A SECOND tap turns on the ignition.
A THIRD tap brings it back to accessory. Now if you open the door here everything will shut off. Let's call this state retained accessory power (RAP)
Now whenever it's in the RAP state, if you tap it will bring it back to ON and keep cycling back and forth.
While in the ON position if you put your foot on the brake and then tap, it will start cranking the engine until it either starts the car or you tap again to go back to the ON position.
When it gets an input from an RPM switch that activates once the car is running above a certain RPM, it stops cranking and we are now in the running state.
At this point tapping will do nothing. So there are no accidental taps and you don't turn the car off at speed.
To turn the car off you need to pull the handbrake up at which point you can tap and it brings you to the RAP state where accessories stay on until you exit the vehicle.
Here is a video that might be easier to understand if you didn't understand some of that.
There are also some mechanical safety features built into the circuit.
The acc and ignition are also on latching relays, so if for some reason power to the chip is lost while the engine is running it won't shut the car down.
If power to the chip is lost when the engine is running it will automatically reset itself to the running state.
I will also be making another reader for the boot release. So you just hold your hand at the bumper and it pops the boot.
I will keep this thread updated as I progress.
