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Bench Talk for Design Engineers

Bench Talk


Bench Talk for Design Engineers | The Official Blog of Mouser Electronics

Computers on Wheels John Donovan

In 1984 John Gage at Sun Microsystems promoted the idea that “the network is the computer.” Gage was a bit ahead of his time; the Internet was just getting off ground—TCP/IP had only been standardized two years earlier—and the Netscape Navigator browser didn’t debut for another 10 years. Today virtually every computer in the world is part of the Internet.

The new frontier is automobiles, which are basically computer networks on wheels. While still rarely connected to the Internet, the 50-100 or more electronic control units (ECUs) in a modern automobile are all part of one of several networks, depending on their function. The primary networks are CAN, LIN, FlexRay, MOST, and Ethernet AVB. Connecting all the network nodes requires as much as a mile of wire in high-end cars.

The Controller Area Network (CAN) is currently the primary automotive network in the cabin, powertrain, chassis, and body systems.

• Active Safety CAN might control millimeter-wave radar, which can sense an oncoming vehicle and initiate a warning sound, braking, and even steering control.

• Car instrumentation, responding to a warning from radar over the CAN bus, could initiate a warning, whether by a sonic alert, spoken warning, and/or a heads up display.

• Reacting to a warning from radar the Brake Control CAN might initiate weak or strong brake control, depending on wheel speed and the proximity of another car.

• Also reacting to warning of a possible crash an MCU connected to seatbelts could pre-tension the belts, lightly at first but strongly if the crash looked immanent.

The Local Interconnect (LIN) network is a low data rate master/slave network that controls things like remote keyless entry, lighting, mirrors, and doors. Via the LIN network the doors may automatically lock when the car starts moving; an alarm sounds when seatbelts aren’t fastened or the car is turned off when the lights are still on; or the rear view mirror and seats automatically re-adjust to previous settings depending on who is driving the car.

In contrast to LIN FlexRay, is a high-speed, reliable protocol for next-generation application such as drive-by-wire. FlexRay systems provide greater accuracy in response to proximity alerts, adding the ability to consider acceleration angle to actively steer and brake a car to avoid a pending collision. This can be especially useful when a braking car starts to skid and slide on a rain slick street.

The Media Oriented Systems Transport (MOST) networks handle in-car multimedia, routing high-quality video, audio, and data within the vehicle. They’re responsible for hands-free phone calls and playing your cell phone music over the car sound system.

Ethernet is too well established and trusted not to have made it into the car, where it generally provides the backbone for polling ECUs in the engine, chassis, and body systems for faults. Ethernet Audio Video Bridging (AVB) competes with MOST to provide high-fidelity digital audio to passengers.

Cars are increasingly able to interact with each other as well as a modern wireless highway infrastructure. Now your car isn’t just a way to get to work or the convenience store—it’s a mobile network node. Now the network is truly the computer, which just happens to be your car.

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John Donovan is editor/publisher of and ex-Editor-in-Chief of Portable Design, Managing Editor of EDN Asia, and Asian editor of Circuits Assembly and Printed Circuit Fabrication. He has 30 years experience as a technical writer, editor and semiconductor PR flack, having survived earlier careers as a C programmer and microwave technician.

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