Microchip Technology Inc

Electronic Compass System

Auto-dimming rear-view mirrors not only increase safety in driving but provide the car OEM with a cost-effective way to deliver value added features, such as electronic compass, to the driver. The electronic compass system determines the direction in which the car is heading as it senses the absolute position and the change in direction of the car using the earth’s magnetic field as a reference. The direction can be displayed using a low-end segmented LCD integrated with the auto-dimming rear-view mirror or in conjunction with the vehicle’s on board navigation display. The sensor technology utilized is either magnetoresistive or inductive sensors.

Design Considerations
  • Robust, general purpose, performance-oriented microcontroller with small footprint
  • Flexible sensor interface
  • Signal conditioning hardware
  • PIC16, PIC18 and PIC24 microcontrollers enable a broad array of diverse on-chip peripherals from IIC to CCP to ADC to SR Latch to CTMU. Thus, providing the system designer an opportunity to match the appropriate peripheral set with the sensing methodology utilized within the electronic compass system. Even with on-chip ADC of the microcontroller, the output signal generated by magneto-resistive sensors generally has a low-level requiring amplification using either on-chip operational amplifiers or stand-alone differential amplifiers, depending on available board space.
  • The output signal generated by the magneto-resistive sensors is generally of a low magnitude, which needs to be amplified before being fed into the ADC module. Microchip provides the user with the option of using stand-alone differential amplifiers or using integrated amplifiers, which saves external component cost and board space. Microchip microcontrollers also have on-board ADC modules, providing the user greater control and flexibility to use the signal data.
  • The inductive sensors are connected to a known resistance value to create an LR oscillator circuit. With change in position, the inductance of the system changes, hence, the frequency of the circuit changes. Timing algorithms developed for the PIC® microcontrollers enable the system to measure the change in frequency of the circuit, to measure the change in inductance value and process the data to determine the direction of change.
  • The on-chip EEPROM peripheral of PIC microcontrollers or stand-alone SEE provides the system designer with a non-volatile memory array to store system variables that may be recovered to identify the last known settings or conditions.
  • Utilizing PIC microcontrollers with on-chip LCD modules support the direct drive of the LCD display, eliminating the need for an incremental LCD driver chip. A Graphics library is readily available to support the system designer’s code development efficiency.
  • With on-chip peripherals to support LIN and CAN communication protocols, the system designer is able to choose the appropriate PIC microcontroller that matches the overall system requirements. Plus, CAN and LIN transceivers options are available to the system designer for the physical layers interface requirements.
Development Tools