[attachment=11777]
HISTORY
The commonly used key systems for locking/unlocking of car doors, turning on/turning off of engine and security systems has been enhanced by the new technology developed under Automotive electronics. The technology is termed as SMART KEY SYSTEM. The rapid growth of new technologies began in early 20th century. Mercedes Benz was the first automotive manufacturing company to implement the SMART KEY SYSTEM technology back in the 1990’s. Locking keys inside a vehicle was all too common experience for many drivers.
On newer cars, keys do a lot more than just lock and unlock doors . Smart keys are part of a computerized system that uses sensors and microchips to automatically unlock the doors and start the vehicle without the use of a key. Smart keys are often shaped more like plastic cards than actual keys.
1) INTRODUCTION
A Smart key System for an automobile includes a control module configured to receive signals about an operation state of the automobile. It also includes a lock preventing circuit controlled by the control module,a knob housing, a user operable start-up knob disposed in the knob housing and a slidable projection on the start up knob controlled by the lock prevention circuit based on the operation state of the automobile.
Briefly summarized, according to one aspect of the present invention, an anti-lockout smart key system for a vehicle comprises a smart key having a built-in transmitter/receiver, a battery, and a mechanical switch. Insertion of the key into a lock opens the mechanical switch deactivating the transmitter/receiver. The system includes a door locking system having a door with a door lock for receiving the smart key and having means for generating door condition signals representing locked, unlocked, open and closed conditions of the door; an ignition locking system having an ignition lock for receiving the key and having means for generating ignition condition signals representing on, off, key inserted and key removed conditions of the ignition lock; a vehicle transmitter/receiver for communicating with the transmitter/receiver in the key; an alarm; and a controller receiving signals from the ignition locking system, door locking system and vehicle transmitter/receiver, the controller activating the alarm and temporarily unlocking the door when the key is left in the vehicle and the door is closed and locked.
Smart Key Systems
The Smart Key System comprises of :
1) The ECU (Electronic Control Unit)
2) DIP Switches
3) Transmitter / Receiver
The Electronic Control Unit
It mainly consists of a Power source, Voltage regulator and a microprocessor. The power source provides DC current. The voltage of the battery may constantly vary due to charging and discharging. Hence a voltage regulator is provided to regulate constant voltage in the circuit. The constant voltage in the circuit ensures that there is no trip or short-circuiting in the main circuit due to excess of voltage.
The microprocessor is heart of the ECU. It monitors the functions, interruptions and carries out the commands that have to be executed.
The control units in the microprocessor identifies the commands to be executed and thus the locking/unlocking door, starting/stopping engine etc tasks will be performed.
The DIP Switches
DIP switch (blue).
A DIP switch has eight tiny switches arranged in a small package and soldered to the circuit board. By setting the DIP switches inside the transmitter, the code that the transmitter actually sends is controlled.
In the above figure, as there are Eight DIP switches, only 256 combinations of codes is possible.
The Transmitter
The transmitter consists of two transistors and a couple of resistors. A two-transistor transmitter, powered by a 9-volt battery, is as simple as a radio transmitter.
The transmitter in the smart key actually transmits the generated codes of commands to be performed. These codes are received at the other end by the receiver present inside the car.
The Modern Arrangements
There is a small chip that creates the code that gets transmitted, and the small silver can (about the size of a split pea) is the transmitter.
• The transmitter's controller chip has a memory location that holds the current 40-bit code. When you push a button on your key fob, it sends that 40-bit code along with a function code that tells the car what you want to do (lock the doors, unlock the doors, open the trunk, etc.).
• The receiver's controller chip also has a memory location that holds the current 40-bit code. If the receiver gets the 40-bit code it expects, then it performs the requested function. If not, it does nothing.
• Both the transmitter and the receiver use the same generator.
METHODOLOGY
The fob that you carry on your keychain or use to open the garage door is actually a small radio transmitter. When you push a button on the fob, you turn on the transmitter and it sends a code to the receiver (either in the car or in the garage). Inside the car or garage is a radio receiver tuned to the frequency that the transmitter is using (300 or 400 MHz is typical for modern systems). The transmitter is similar to the one in a radio-controlled toy.
• The transmitter's controller chip has a memory location that holds the current 40-bit code. When you push a button on your key fob, it sends that 40-bit code along with a function code that tells the car what you want to do (lock the doors, unlock the doors, open the trunk, etc.).
• The receiver's controller chip also has a memory location that holds the current 40-bit code. If the receiver gets the 40-bit code it expects, then it performs the requested function. If not, it does nothing.
• Both the transmitter and the receiver use the same pseudo-random number generator
• When the transmitter sends a 40-bit code, it uses the pseudo-random number generator to pick a new code, which it stores in memory. On the other end, when the receiver receives a valid code, it uses the same pseudo-random number generator to pick a new one. In this way, the transmitter and the receiver are synchronized. The receiver only opens the door if it receives the code it expects.
• If you are a mile away from your car and accidentally push the button on the transmitter, the transmitter and receiver are no longer synchronized. The receiver solves this problem by accepting any of the next 256 possible valid codes in the pseudo-random number sequence. This way, you (or your three-year-old child) could "accidentally" push a button on the transmitter up to 256 times and it would be okay -- the receiver would still accept the transmission and perform the requested function. However, if you accidentally push the button 257 times, the receiver will totally ignore your transmitter. It won't work anymore.
So, what do you do if your three-year-old child DOES desynchronize your transmitter by pushing the button on it 300 times, so that the receiver no longer recognizes it? Most cars give you a way to resynchronize. Here is a typical procedure:
• Turn the ignition key on and off eight times in less than 10 seconds. This tells the security system in the car to switch over to programming mode.
• Press a button on all of the transmitters you want the car to recognize. Most cars allow at least four transmitters.
• Switch the ignition off.
Given a 40-bit code, four transmitters and up to 256 levels of look-ahead in the pseudo-random number generator to avoid desynchronization, there is a one-in-a-billion chance of your transmitter opening another car's doors. When you take into account the fact that all car manufacturers use different systems and that the newest systems use many more bits, you can see that it is nearly impossible for any given key fob to open any other car door.
You can also see that code capturing will not work with a rolling code transmitter like this. Older garage door transmitters sent the same 8-bit code based on the pattern set on the DIP switches. Someone could capture the code with a radio scanner and easily re-transmit it to open the door. With a rolling code, capturing the transmission is useless. There is no way to predict which random number the transmitter and receiver have chosen to use as the next code, so re-transmitting the captured code has no effect. With trillions of possibilities, there is also no way to scan through all the codes because it would take years to do that.