Vermes
Advanced Member level 4
Originally immobiliser was a simple system that couldn't be modified in any way. It consisted of only one chip with gates and few RC systems. The original system cannot be unlocked when door is open – every open door is detected as break-in, even if the driver went out to scrape ice from windscreen. That is how the idea came to make a car immobiliser of own construction.
Assumptions:
- protection as a hidden button
- anti-theft and anti-jacking protection
- LED signalling (in this simulation alarm)
- sound signal
- possibility of integrating the service mode (deactivating so you don't have to give location of the switch to the service)
- immobilization of the vehicle by cutting off the ignition
- possibility of opening the door and inform the system that the driver is inside and there is no need to initiate the anti-jacking action
- extremely low power consumption
- simple and compact design
Program was written in WinAVR environment and it takes about 1,8kB. A watchdog is activated, it resets the system when needed, the processor works on internal RC 4MHz. Counting the time is done on timer 1, controlling LED signalling and buzzer in interrupt on timer 0, each 50ms. The system has input protection against overvoltage, transildiode on power supply +5V, varistor on power supply input, two inputs controlled by the mass and one +12V by the key.
The plate is one-sided, made by iron method.
The whole with LED takes about 8-9mA in standby mode and 55mA with the pump relay turned on.
The principle of unset is simple, open the door, then get on the car. When turning the key, the calculation starts (indicated by a slow at first, then faster and the fastest flashing LED steady light and the corresponding beeps). At first, the signals are very discreet, so the burglar doesn't know when they come from and where the system is, at the same time they are loud enough (getting louder) so a car user do not fell into his own trap. Counting lasts 25sec until turn off the fuel pump. After that the system locks up, shuts off the pump, lights the LED and off sounds. It can be wake of this state by pressing the discreet button. Pressing this button during counting interrupts it, the LED goes out, the signal stops. If the car is off and if the ignition is turned off, within 15 seconds without opening the door again the car is started again, re-authorized would not be needed (for safety). However, if the ignition is switched off for longer than 15 seconds or the door would be open, the car would go into the state of imitation of the alarm what means single brief flashes each more than second. If the door is opened (in fact, closed, because the closure is controlled rather than opening) when the engine is running, the countdown 25sec begins. If it wouldn't be authorized by pressing the button, the car turns off. The door can be also opened, the button pressed at once and thanks to that, the door can be closed without authorization. Longer (8sec) holding the button pressed while the ignition is on, causes switching the system into service mode – indicated by a steady light of the LED. Thanks to that, there is no need to inform the service about the presence and location of the button. Service mode can be turned on the same way as it is turned off. The fact of being on and off is written in EEPROM, so even disconnecting the clamps does not cause spontaneous activation of the immobiliser.
Link to original thread (useful attachment) – Immobiliser samochodowy na ATtiny2313
