Car Electronics Page

    General information

    Global demand for OEM automotive electronics is increasing at considerable higher than that of vehicle production itself. Notable gains are expected in safety, entertainment and communications systems as well as in emissions controls and engine management systems. All sorts of electronics are now present in the car. It is predicted that in the near future as much as 20-30% of the cost of a car may be due to electronics.

    The following classification of electronics in modern car can be made:

    • Engine and chassis control electronics: engine control, automatic gearbox, ABS/ASR,intelligent cruise control, etc.
    • Cabin comfort: air conditioning, dashboard, trip computer, display range, radio, telephone, navigation, etc.
    • Body: intelligent switch unit, (lights, wipers, locks, etc.), anti-finger trap system for power windows, power seat, column switch, alarm, etc.

    As a result of the high diversity of electronics used, a wide range of microcontrollers is used. 32 bit 68332 is often used in the united state to combine airconditioning and engine control and automatic gear. 16 bit 80C166 and TMS370 are favourites for engine control. 8 bit microcntrollers are used for small devices. Popular 8 bit microcontrollers in car electronics are H8 (dashboard electronics), 8051 (radio) and 68hc11 (dashboard or trip computer). Also some 4 bit NEC microcontrollers are used in some low-end electronic dashboard applications.

    A major technology shift is being prepared in the car wiring. The idea is to replace the application specific point to point wiring with some control network, and consequently reducing wiring cost and enhancing connecting reliability. The diversity of automotive electronics and the fact that a system approach is used has led to approaches where the network speed and the message system are tailored. Many automotive networks include object-oriented concepts. Several initiatives have been taken all over the world for car networks. Here is few systems to mention:

    • Class A (body) multiplexing experimented by Renault and PSA, used to connect low-end equipment e.g. lights..
    • I2C control network with a token bus protocol for radio, telephone, "satellite" column switch and shared display range
    • J1850 is an automotive local area network (in the car) standardized by SAE. J1850 is mainly used in USA.
    • CAN (Controller Area Network) was initiated by Bosch with the collaboration of Intel. CAN has been adopted worldwide for trucks and is in wide use in Europe, also adopted by some US manufacturers. CAN is a serial, asynchronous, multi-master communication protocol for connecting electronic control modules in automotive and industrial applications. CAN was designed for applications needing high levels of data integrity and data rates of up to 1 Mbit/s.)
    • VAN is a French initiative as an alternative to CAN.

    There are also other networking systems competing on car networks sector:

    • FlexRay is a car control network developed by BMW in 1990s (origianlly called Byteflight). Is is supported by BMW, Daimler-Chrysler, Freescale and Philips. FlexRay is designed for x-by-wire subsystems like breaks and suspension control. The maximum speed for the bus is 10 Mbit/s using two communication channels.
    • LIN (Local Interconnect Network) is an end-to-end solution for in-vehicle and industrial control communication and networking. It is a single-wire serial communications protocol based on the common SCI "UART" byte-word interface.
    • MOST (Media Oriented System Transport) is a car multimedia network that used transport speed 50 Mbps over plastic optic fiber.

    Concerning software structure, a majority of systems are based on the endless loop approach. Cyclic kernels are also used as alternative to the endless loop approach. The multithread approach is still rarely used, except in high-end embedded systems with real-time constraint (engine control) or in highly structured systems (radio equipment).

    The automotive market is demanding for electronics devices. Electronics must operate underextreme temperatures (easly from -30 to +50 degrees celsiues) and be able to withstand vibration, shock, and EMI. The electronics must be reliable, because a failure that causesan accident can (and does) result in multi-million dollar lawsuits. Reliability standards are high - but because these electronics alsocompete in the consumer market - they have a low price tag.Wires, fuses and connectors are found in every electrical device, and especially in cars. Along with increased reliability, the complexity of car wiring systems has increased dramatically. Cars now have literally thousands of circuits. This page will go through some of the key components in your car's wiring.

    Electrical power in car

    Cars nowadays use 12V electrical system. Keep in mind that 12V is not exactly 12V in an automotive environment. Voltage is anywhere between 7 and 14.5V (starting to running engine at full RPM with no electrical consumption and a fully charged battery and an "optimistic" voltage regulator on the alternator). A typical voltage when car is running or stopped is around 11-15V depending on the battery condition, is the motor running and how much electrical load is active at this particular time in the car. ). Then there are large spikes of many 10s of volts (usually 80V is considered "normal") to take into account. When doing electrical design that goes to car environment, the requirements must be fully understood or problems will arise. Car battery supplies power to the starter and ignition system to start the engine, supplies the extra power necessary when the vehicle's electrical load exceeds the supply from the charging system and acts as a voltage stabilizer in the electrical system. Car batteries are built using lead acid cells. They have a cell voltageof around 2 volts (means 6 cells in series makes 12V battery).Normal 12V car battery is designed to be quite robust. It canbe carged with almost any reasonably current limited constantvoltage source of around the nominal voltage of the battery(for example 13.5V for 12V car battery). Car batteries are built for heavy currents but DO NOT deep dischargethem, only shallow discharge. If you repeatedly run a car battery down tomuch below 50% of capacity you will seriously shorten its life. Warnings on car batteries:Car batteries contain dangerous acid hare heavy, so handle carefully.Charging car batteries can generate highly flammabble hydrogen,so it is best to charge those only in well ventilated spaces.Car batteries have very large short circuit current (hundredsof amperes), so do not short circuit them (a fuse near batteryterminal is essential for safety to avoid wire fires in short circuithappens).

    Car networks

    Modern car includes lots of electronics which is networked together.For this applications there are many networks developed. The most widely used car networks are CAN and LIN.


      CAN (Controller Area Network) is an automation bus used in automotive applications and in industrial automation.Controller Area Network (CAN) is a fast serial bus that is designed to provide an efficient, reliable and very economical link between sensors and actuators. CAN uses a twisted pair cable to communicate at speeds up to 1Mbit/s with up to 40 devices. Originally developed to simplify the wiring in automobiles.CAN supports operation up to 40m at 1 Mbps speed without repeaters, and up to1 km at 20 kbps speed. Can uses twisted pair wiring. Can uses CSMA bus arbitration. CAN data packets are 8 bytes long and use 11-bit packet identifier.


      Local Interconnect Network (LIN) protocol was designed by a consortium of European auto manufacturers as a low-cost, short-distance, low-speed network for automotive application. LIN is designed to communicate changes in switch settings and respond to switch changes, it is intended to communicate events that happen in "human" time (hundreds of milliseconds).LIN (Local Interconnect Network) is a low cost serial communication system intended to be used for distributed electronic units in vehicles, which complements the existing portfolio of automotive multiplexing networks. This open standard for class-A communication (up to 20kbit/s) was introduced in 2000 and is tailored towards sub-busses operating below CAN.

      ODB II and ither diagonig buses

      On-Board Diagnostic systems are in most cars and light trucks on the road today. During the '70s and early 1980's manufacturers started using electronic means to control engine functions and diagnose engine problems. This was primarily to meet EPA emission standards. Through the years on-board diagnostic systems have become more sophisticated. OBD-II, a new standard introduced in the mid-'90s, provides almost complete engine control and also monitors parts of the chassis, body and accessory devices, as well as the diagnostic control network of the car.All cars built since January 1, 1996 have OBD-II systems. Manufacturers started incorporating OBD-II in various models as early as 1994. Some early OBD-II cars were not 100% compliant. Basically what we have in a automobile built after 1996 ( USA/Europe/Asia )is an automobile LAN, using 1 of 3 protocols, with a central CPU, sensors forautomobile telemetry, Transceivers and/or receivers and transmitters, bus arbitration etc. The buzzwords hare are OBD-II, SAE, J1850 Diagnostic Scanners, CAN Bus etc. All OBD-II cars have a connector located in the passenger compartment easily accessible from the driver's seat. Check under the dash or behind or near the ashtray. A cable is plugged into the OBD-II J1962 connector and connected to AutoTap or another scan tool. OBD-II signals are most often sought in response to a "Check Engine Light" appearing on the dashboard or driveability problems experienced with the vehicle. The data provided by OBD-II can often pinpoint the specific component that has malfunctioned, saving substantial time and cost compared to guess-and-replace repairs.

      Other car networks

      • Auto network runs 25 Mbits/s over UTP wiring - The SMARTwire X technology and physical layer modules offer a fast and low-cost means of upgrading existing optically networked devices such as radio head units and CD chargers so they can communicate over UTP cables.    Rate this link
      • MOST Cooperation - Through the MOST Cooperation, all members combine their expertise and ambitious efforts to establish and refine a common standard for today and tomorrow's needs of automotive multimedia networking. Since the Cooperation was founded in 1998, 20 international carmakers and more than 50 key component suppliers are now working with the MOST Technology and contributing towards its innovation.    Rate this link

    Future car electrical systems

    The demand for luxuries in cars has grown to where 12/14-Volts is just simply not enough. The automotive sound enthusiasts are going to benefit greatly as amplification will be much easier and cleaner with 3 times the voltage availble. The standard that was recently agreed to by automakers and suppliers in Europe and the U.S. is a 36-/42-volt standard. Specifically, it is a tripling of the current voltage for both battery output (from 12 to 36) and generator voltage output (from 14 to 42). Vehicles with these next generation electrical systems will likely have dual batteries (12-volt and 36-volt) or at least a stepped-down, 12-volt circuit on board so that all electrical components don't have to change over at once. It seems cars will have dual systems for a while for legacy equipment.Beginning in 2004, the U.S. auto industry will begin its move from the 12-volt battery (14 volts at the generator/alternator) electrical systems toward a 42-volt standard, with 25 to 50 percent of new vehicles incorporating 42V electrical architectures by 2010, and all new cars by 2020.

    Car circuits

      Other accessories

      • Adaptive Wiper - windshield wiper controller circuit    Rate this link
      • Speed-limit Alert - This circuit has been designed to alert the vehicle driver that he has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving. There is a strict relation between engine's RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached. Its outstanding feature lies in the fact that no connection is required from circuit to engine. This circuit should be adaptalble for most combustion engine vehicles.    Rate this link

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