Automotive Electronics
Figure 3: Microchip’s PIC16F1829LIN RGB Ambient Lighting Board
scenarios make the usage of a microcontroller, such as a PIC MCU with non-volatile memory, inevitable. Furthermore, the need to network those RGB lighting nodes in the vehicle, along with the desire for diagnostics, calls for a suitable low-cost communication protocol. While the first generations of interior lighting were individually wired, the latest generations and recent developments at OEMs make use of the well-known, cost- effective LIN / J2602 communication bus. The LIN communication speed of 19.2k baud is sufficient to support colour changing and lighting scenarios without a noticeable impact on the driver or passengers. More recently, LIN communication with auto-addressing capability is being considered for this type of application by some car makers. There are several known auto-addressing methods, each with pros and cons (see Figure 2). Common to all of them is that they add costs to the silicon, when compared with standard LIN communication. However, those additional costs yield reduced logistics costs at the OEM and Tier1 levels.
Addressing space constraints Typical interior-lighting applications are very space constrained. Light nodes are embedded in switches, cup holders, door handles, dashboards, seats, reading lights, footwell areas and overhead consoles. The available space for the electronics is often squeezed in to an area of 10 mm x 20 mm or less, driving small package solutions in SSOP, QFN and DFN housing. Ambient temperature and self heating in such environments require careful heat management, for semiconductor devices with low power dissipation and extended operating temperature ranges from -40°C to 125°C. Usually, the nodes are connected to terminal 30 and thus require very low standby current, significantly below 100 µA.
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Microchip’s Automotive Ambient Interior Lighting Module Reference Design demonstrates microcontroller-based control of RGB LED devices. This module can be controlled remotely by a master body controller, via the LIN bus. These modules are offered in a very compact 10x20 mm form-factor board, and are comprised of a PIC16F1829LIN solution, including a LIN transceiver, voltage regulator, 8-bit PIC microcontroller and RGB LED. LIN commands are interpreted by the module to control colour mixing (16,383 colours) and intensity (1023 levels).
The kit ships with four modules to assign as lighting zones in a LIN or J2602 network. These modules can also be used in conjunction with Microchip’s LIN Serial Analyzer to create a working LIN RGB network, straight out of the box. A microcontroller-based solution
provides the flexibility and integration required for future RGB LIN-based interior lighting applications. Carefully considered system architecture designs allow the usage of low-cost 8-bit microcontrollers without compromising performance. This enables OEMs to offer colour interior lighting in high-volume, mass-market vehicle models, increasing their value proposition and enhancing driving comfort and safety. Features such as approach sensing and capacitive-touch switches are additional functions that are easy to implement at almost no additional cost with PIC microcontrollers, thus further enhancing the value of the system.
Microchip |
www.microchip.com
Johann Stelzer is European Automotive Marketing Manager, Andreas Reiter Senior Business Development Manager and Frank Ziegenhorn Principal Automotive Applications Engineer at Microchip Technology
Components in Electronics October 2012 11
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