This OnStar® system consists of the following components:
| • | Communication Interface Module (CIM) |
| • | OnStar® button assembly |
| • | Microphone |
| • | Cellular/GPS antenna |
| • | Back Up Battery (BUB) |
This system also interfaces with the factory installed vehicle audio system.
Communication Interface Module (CIM)
The communication interface module (CIM) is a cellular device that allows the user to communicate data and voice signals over the national cellular network. Power is provided by a dedicated, fused B+ circuit. Ground is provided through the vehicle wiring harness attached to the module. The ignition state is determined by the CIM through serial data messaging.
Dedicated circuits are used to connect the CIM to a microphone, the button assembly, and to command the status LED. The CIM communicates with the rest of the vehicle over the serial data bus.
The module houses 2 technology systems, one to process GPS data, and another for cellular information. The cellular system connects the OnStar® system to the cellular carrier’s communication system by interacting with the national cellular infrastructure. The module sends and receives all cellular communications over the cellular antenna and cellular antenna coax. GPS satellites orbiting earth are constantly transmitting signals of their current location. The OnStar® system uses the GPS signals to provide location on demand.
The module also has the capability of activating the horn, initiating door lock/unlock, or activating the exterior lamps using the serial data circuits. These functions can be commanded by the OnStar® Call Center per a customer request.
OnStar® Button Assembly
The OnStar® button assembly may be part of the interior courtesy lamp assembly, or a separate, stand alone unit. The button assembly is comprised of 3 buttons and a status LED. The buttons are defined as follows:
| • | The answer/end call button, which is black with a white phone icon, allows the user to answer and end calls or initiate speech recognition. |
| • | The blue OnStar® call center button, which displays the OnStar® logo, allows the user to connect to the OnStar® call center. |
| • | The emergency button, which displays a white cross with a red background, sends a high priority emergency call to the OnStar® call center when pressed. |
The CIM supplies 10 volts to the OnStar® button assembly on the keypad supply voltage circuit. When pressed, each button completes a circuit across a resistor allowing a specific voltage to be returned to the CIM on the keypad signal circuit. Depending upon the voltage range returned the CIM is able to identify which button has been pressed.
The OnStar® status LED is located with the button assembly. The LED is green when the system is ON and operating normally. When the status LED is green and flashing, it is an indication that a call is in progress. When the LED is red, this indicates a system malfunction is present. In the event there is a system malfunction and the OnStar® system is still able to make a call, the LED will flash red during the call.
If the LED does not illuminate, this may indicate that the customers OnStar® subscription is not active or has expired. Push the blue OnStar button to connect to an advisor who can then verify the account status.
Each LED is controlled by the CIM over dedicated LED signal circuits. Ground for the LED is provided by the wiring harness attached to the button assembly.
OnStar® Microphone
The OnStar®, or cellular microphone, is located in the interior courtesy lamp assembly. The CIM supplies approximately 10 volts to the microphone on the cellular microphone signal circuit, and voice data from the user is sent back to the CIM over the same circuit. A cellular microphone low reference circuit or a drain wire provides a ground for the microphone.
Cellular/GPS Antenna
The cellular antenna is the component that allows the OnStar® system to send and receive data over airwaves by means of cellular technology. The antenna is connected at the base to a coax cable that plugs directly into the CIM.
The GPS antenna is used to collect the signals of the orbiting GPS satellites. Within the antenna is housed a low noise amplifier that allows for a more broad and precise reception of this data. The antenna is connected at the base to a coax cable that plugs directly into the CIM. The cable also provides a path for DC current for powering the antenna.
The OnStar® Call Center also has the capability of communicating with the vehicle during an OnStar® call to retrieve the latest GPS location and transmit it to the OnStar® Call Center. A history location of the last recorded position of the vehicle is stored in the module and marked as aged, for as long as the module power is not removed. Actual GPS location may take up to 10 minutes to register in the event of a loss of power.
Audio System Interface
When the OnStar® requires audio output, a serial data message is sent to the audio system to mute all radio functions and transmit OnStar® originated audio. The OnStar® audio is transmitted to the vehicle audio system by a dedicated signal circuit and a low reference circuit.
The audio system will mute and an audible ring will be heard though the speakers if the vehicle receives a call with the radio ON.
On some vehicles, the HVAC blower speed may be reduced when the OnStar® system is active to aid in reducing interior noise. When the system is no longer active, the blower speed will return to its previous setting.
