For those looking into enhancing their car security system or simply keen on a DIY project, programming your own remote control for your car alarm is an exciting venture. Utilizing readily available components and a bit of coding, you can create a custom remote that not only arms and disarms your car alarm but also integrates additional functionalities. This article delves into a fascinating project that uses an Arduino and a Xenon Design keychain Tx/Rx set as a foundation for building a personalized car alarm remote control system.
Project Overview: Building a Custom Car Alarm Remote
This project leverages the affordable Xenon Design keychain Tx/Rx set as the core radio communication platform. The primary objective is to program an Arduino to execute a series of “remote functions” for your car. This goes beyond basic locking and unlocking, aiming to integrate features like window control, trunk release, and even interior lighting.
A noteworthy aspect of this project is the implementation of EEPROM wear-leveling. This clever technique is designed to extend the lifespan of the EEPROM when saving crucial states like arm/disarm and alarm status. By cycling through EEPROM cells and writing data multiple times to each before moving to the next, the system ensures longevity and reliability, addressing the typical EEPROM write cycle limitations.
Key Components and Pin Configuration
Building your own car alarm remote control requires careful consideration of both hardware and software. The project utilizes specific I/O pins on the Arduino to manage various car functions. Here’s a breakdown of the planned pin configuration:
- Digital Pins:
- 0: Serial RX (for potential communication with other devices)
- 1: Serial TX (for potential communication with other devices)
- 2 (Interrupt 0): Data Received (signals remote button press)
- 3 (PWM) (Interrupt 1): Motion sensor (future implementation)
- 4: Window Direction Control
- 5 (PWM): Interior Lights (for dimming control)
- 6 (PWM): Ignition kill relay (for security)
- 7: Activate Window 1 (Driver side)
- 8: Activate Window 2 (Passenger side)
- 9 (PWM): Door Lock
- 10 (PWM): Door Unlock
- 11 (PWM): Siren/Speaker (for alarm sounds)
- 12: Trunk Release
- 13: Brake Light Flash (for visual alarm indication)
- Analog Pins:
- a0: Button A (Remote button input)
- a1: Button B (Remote button input)
- a2: Button C (Remote button input)
- a3: Button D (Remote button input)
- a4, a5: Available for future expansion
This pin layout is designed to accommodate a wide range of functionalities, drawing upon the Arduino’s PWM capabilities for features like interior light dimming and siren control. The analog pins are dedicated to reading input from the Xenon receiver buttons.
Remote Button Functions and Customization
The remote control, built around the Xenon Tx/Rx system, is designed with four buttons, each configurable for single and combined press actions to maximize functionality. Here’s a breakdown of the planned button functions:
- A: Lock / Arm – Pressing button A will lock the car doors and arm the car alarm system.
- B: Unlock / Disarm – Button B will unlock the doors and disarm the alarm.
- C: Special Modes – Button C acts as a modifier, enabling additional functions when combined with other buttons:
- C+D: Open trunk
- C+A: Roll both windows up
- C+B: Roll both windows down (partially)
- C (hold) + A: Roll driver-side window up
- C (hold) + B: Roll driver-side window down
- D: Interior Lights On – Pressing D will turn on the interior lights for a timed duration (e.g., 1 minute) with a fade-in/fade-out effect.
- D (hold) + A: Roll passenger-side window up
- D (hold) + B: Roll passenger-side window down
The Xenon Tx/Rx system’s button detection is sequential; it only registers the first button pressed in a simultaneous press until all buttons are released and re-pressed. This characteristic is important to consider when programming the button combinations.
Code Snippet and Functionality (Conceptual)
Below is an initial code snippet demonstrating the fundamental aspects of reading button presses and initiating the EEPROM wear-leveling process. It’s important to note that this is a work in progress and not a fully functional code base.
#include <eeprom.h>
boolean buttonPressed = false;
volatile boolean buttonA = false;
volatile boolean buttonB = false;
volatile boolean buttonC = false;
volatile boolean buttonD = false;
boolean armed = false;
boolean readArmed();
void setup() {
attachInterrupt(0, toggleButtonPress, RISING); // Interrupt for data receive pin
Serial.begin(9600);
}
void loop() {
if (buttonPressed) { // Button press detected
if (buttonA) {
// Lock/arm functionality to be implemented here
}
delay(50); // Debounce delay
}
}
boolean readArmed() {
boolean state = false;
unsigned int eepromPos = 0;
byte eepromByte = EEPROM.read(eepromPos);
while (eepromByte == 255) { // Find the last used EEPROM byte
eepromPos++;
if (eepromPos == 1024) break;
eepromByte = EEPROM.read(eepromPos);
}
while (bitRead(eepromByte, 7)) { // Toggle state bits for wear-leveling
eepromByte = eepromByte << 1;
}
return state;
}
void toggleButtonPress() {
buttonA = (analogRead(0) > 800);
buttonB = (analogRead(1) > 800);
buttonC = (analogRead(2) > 800);
buttonD = (analogRead(3) > 800);
buttonPressed = true;
}This code provides a basic structure for detecting button presses and includes a rudimentary EEPROM read function as a starting point for the wear-leveling mechanism. Further development is needed to implement the full range of remote functionalities and refine the EEPROM management.
Expanding Functionality: Relays and Car Integration
To control physical car functions such as windows, door locks, and the trunk release, the project plans to use relays. A custom shield, potentially designed in Fritzing, will house these relays. Reinforcing the current lines for power-hungry components like window motors is also considered to handle the necessary amperage.
- Window Control: Will utilize 3 relays per window:
- 1 DPDT (Double Pole Double Throw) relay for reversing polarity to control window direction (up/down).
- 2 DPST (Double Pole Single Throw) relays to completely disconnect power from the window switches when inactive, enhancing safety and preventing accidental activation.
- Door Locks: 2 SPST (Single Pole Single Throw) 5V relays will be used to supply +12VDC to the car’s existing door lock relay system.
- Trunk Release: Another SPST 5V relay will be implemented to send a 12V signal to the car’s trunk release mechanism.
- Ignition Cutoff: A 10A SPST normally-closed relay will serve as an ignition kill switch, activating if the alarm is triggered, adding an extra layer of security.
- Brake Light Flash: The implementation for brake light flashing is still under investigation, requiring analysis of the car’s wiring diagram to ensure safe and effective integration.
Motion Sensor and Interior Lights (Future Enhancements)
While the project currently doesn’t incorporate a motion sensor, a pin has been reserved for future implementation. The challenge lies in identifying a suitable vibration sensor compatible with Arduino for reliable motion detection.
For interior lights, the plan is to use a PWM output from the Arduino connected to a MOSFET. This setup would enable smooth dimming and fading effects, mirroring the sophisticated interior lighting features found in modern vehicles.
Serial Communication with MPGuino (Advanced Feature)
An ambitious extension of this project is to establish serial communication between the car alarm system and an MPGuino (an Arduino-based car computer). This communication could enable the MPGuino screen to display relevant alarm system information.
Potential uses for this integration include:
- Displaying alarm status (armed/disarmed) on the MPGuino screen.
- Putting the MPGuino into a “screensaver” mode when the car is armed, potentially displaying a security-related message.
- Receiving notifications from the MPGuino if the car is running, which could be used to prevent accidental arming of the alarm while the engine is on.
This serial link would essentially transform the MPGuino screen into an extended display and interaction interface for the DIY car alarm system.
Conclusion
This Arduino-based car alarm remote control project represents a significant step towards creating a customized and feature-rich car security system. By combining readily available hardware with creative programming and thoughtful system design, it’s possible to achieve a level of functionality and personalization that goes beyond standard aftermarket car alarms. While still under development, the project showcases the potential of DIY electronics in enhancing vehicle security and convenience. For anyone interested in learning How To Program Remote Control For Car Alarm systems, this project provides a valuable and insightful example.
