Remote Car Starter - Controlling the Motorola c168i with Arduino

I have began making progress on my remote car starter project. The basic concept is to build a home brew version of the Viper SmartStart system. My version will utilize text messages to relay the commands from my cell phone to the car via the Motorola c168i pay-as-you-go phone.

The first steps to getting this project started are learning the ropes of communicating with the c168i via the TTL serial port in the 3/32" headset jack on the top of the phone. The phone uses what are called "AT commands." Many phones can be controlled using these commands but each phone will not necessarily work with every command. There are also other quirks to account for such at the excessive power management of the c168i that requires sending something over the serial connection to wake the phone up before sending an actual command.

To connect your Arduino to the c168i you will need a 3/32" headset plug. I used part 274-0298 from Radio Shack. The connection uses three wires: ground, TX (transmit) and RX (receive). The tip on the 3/32" headset plug is the TX signal and connects to pin 1 on the Arduino, the ring is connected to the RX signal or pin 0 and the shield is connected to ground.

Below you will find the basic test sketch I used. Every line except for the repeated delay commands is commented to explain what it does. Eventually the delays will be removed and I will program the Arduino to listen for an ok response or error from the phone before proceeding to the next command.

void setup() {

pinMode(13, OUTPUT); // Initialize pin 13 as digital out (LED)

Serial.begin(4800); // Open serial connection at baud rate of 4800

delay(500); // Wait half a second

Serial.println("AT"); // Sends AT command to wake up cell phone

delay(500);

Serial.println("AT+CMGF=1"); // Puts phone into SMS mode

delay(1000); // Wait a second

Serial.println("AT+CMGW=\"+15555555555\""); // Creates new message to number

delay(1000);

Serial.print("This message was generated by Arduino!"); // Message contents

delay(1000);

Serial.println(26, BYTE); // equivalent (signals end of message)

delay(1000);

Serial.println("AT+CMSS=1"); // Sends message at index of 1

delay(10000);

Serial.println("AT+CMGD=1"); // Deletes message at index of 1

}

void loop(){

digitalWrite(13, HIGH); // set the LED on

delay(250); // wait for 1/4 a second

digitalWrite(13, LOW); // set the LED off

delay(250); // wait for 1/4 a second

}

Useful Resources

• http://biobug.org/index.php/2010/02/19/lotd-clean-your-cell-phone/
• http://code.google.com/p/sserial2mobile/
• http://www.tigoe.net/pcomp/resources/archives/avr/000749.shtml
• http://wiki.forum.nokia.com/index.php/Using_AT_commands_to_send_and_read_SMS