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
- 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.
- 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
- 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.