Optical buses and connectors for cars. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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Automotive electronics, which have received great development in recent years, require fast and reliable transmission of large amounts of information. For this purpose, the optical system "MOST" (Media Oriented System Transport) [1-4] was developed. Specialists from the Tyco Electronics concern took part in the development of the concept of building this system and components for it. The "MOST" system has been successfully tested, and AMP catalogs already have sections where you can find the parameters of the system's connectors.

The main elements of the car's electronic system are shown in Fig.1. The amount and type of data transmitted depends on the complexity of the equipment used in the vehicle and on its functional purpose (control, regulation, communication or entertainment).

Rice. 1. The main elements of the car's electronic system

The components of a quick control system (for example, a motor or a drive) are connected to each other by a CAN bus (in fig. 1 CAN C). This bus carries electrical signals and uses copper wires for the bus.

The communication system provides unidirectional data transmission, such as radio (AM/FM), TV data (DAB) and navigation (GPS) and bi-directional telephony (GSM).

Until recently, entertainment electronics consisted of a radio, a laser disc player, a navigation system and telematics. At present, along with the classic radio station, it includes a car telephone, a GPS system screen, service elements and a newly created voice alarm system. In the future, it is planned to introduce new modules that will allow the use of several subsystems simultaneously (Fig. 1). All elements of systems for rapid regulation, control, communication, entertainment and voice notification are connected by a bus. The rapidly increasing functionality of all subsystems requires an increase in bus performance. The required information transfer rates are given in Table 1.

Table 1

According to modern views, a system-wide bus in cars should be built using an optical line. In addition to higher performance, the optical line provides good electromagnetic compatibility.

To study the possibility of building optical systems and introducing them into mass production, a consortium of firms with the participation of Tyco Electronics AMP designed the D2B bus. For the first time, this tire was used in the new S-class of Daimler Chrysler cars. The bus combined a radio and navigation system, an amplifier, a CD player, a public address system and a car phone into one system. A fiber optic line is used for data transmission. The data transfer rate in the D2B bus is about 5.6 Mbps.

Structure of the MOST system

The MOST system is a product of a consortium of German and international car manufacturers. The topological structure of the system is a ring (Fig. 2). Light signals travel along a light guide line from one device to another.

Rice. 2. Structure of the MOST system

In each device, the received light signals are converted into electrical signals, processed by the MOST processor, and again converted into light signals using an LED. The data transfer rate is 24.8 Mbps. Based on experimental tests, it was found that the system should have the following properties:

• the system must have a central system clock that provides bus clocking,
• the possibility of upgrading the system (plug and play) should be provided, i.e. connect a new or exclude one of the existing devices,
• there should be MOST specifiers that compensate for small signal differences between system nodes,
• each device has access to the bus at any time.

To ensure high reliability, optical connectors must meet the requirements that apply to electrical connectors:

• the fixation of the wires in the connectors must withstand a maximum force for disconnection of 60 N without damage.
• the allowable temperature range should be from -40 to +85 C. with an air humidity of 95%.
• connectors must withstand specified climatic, vibration and shock loads.

In addition, for optical systems, it is mandatory that the power consumption be equal to the difference between the transmitter power and the receiver sensitivity. During operation, scratches may occur on the optical surface, films may appear due to exposure to cigarette smoke and gas release from plastics, as well as dust deposits, etc. Therefore, transmitters must be provided with adjustments to compensate for the effect of negative factors. Tyco Electronics AMP is ready to supply components for MOST systems that meet these requirements.

MOST System Components

The most complex element of the MOST system is the MOST processor and its software. The second element is the data bus. When developing the requirements for the bus, one should take into account the large difference between the connected elements from each other. The third element of the MOST system is the communication system. It includes linking the fiber optic transmitter (FOT) to the MOST processor, linking the fiber to the FOT, and the connectors in each device, the sleeves, and the light guide wires themselves. The main elements of the communication system of the MOST system are shown in Fig.3.

Binding devices to light guide lines

To tie fixtures to light guide lines, Tyco Electronics AMP develops products that allow for the insertion of new elements. There are connectors for one and two light guide lines, which, due to their special shape, are designated "Pigtail" (Fig. 4). The reason for separating optical connectors from connection elements with electro-optical converters was the possibility of more effective protection against electromagnetic influences, the interchangeability of transmitting and receiving elements, and more effective protection of the optical surface. For special cases, "Pigtail" integral elements are available for sale, which are coordinated with existing devices. They are compact and interchangeable. The transmitting and receiving elements of the functional modules of the MOST system consist of a CMOS chip and one high-speed PIN diode. The transmission speed of these elements can reach 25 Mbps.

Rice. 3 Communication system components of a MOST system a) light guide connectors 1, 2 b) standard modules 3, 4, 5 c) light guide lines

Standard modules

To bind devices to the MOST bus, there is a complete range of modules (Fig. 5) with 2 or 4 optical connectors and 12, 20 or 40 electrical contacts. All components comply with the requirements established by the MOST consortium and have the appropriate optical, electrical and mechanical parameters.

Fig.4. "Pigtail" connectors for one and two light guide lines

Fig.5. Modules: a) 2 optical connectors and 20 electrical contacts b) 4 optical connectors and 40 electrical contacts

Tests have shown that good protection of optical surfaces as well as device and cable connectors can be guaranteed.

Couplings

Optical couplers are required for connecting new devices to the MOST bus, for cable harness communication, and for service purposes. Single-pole and two-pole variants of couplings have been developed. They are compatible with the two-pole connectors of the modules described above in accordance with the MOST Consortium guidelines.

light guide wires

A new optical fiber has been developed for the MOST bus based on the tests of the previous D2B system. It has better elasticity, is resistant to fire, pressure and does not change transparency. The special inner sheath guarantees excellent mechanical and optical properties and ensures easy machinability. The operating temperature range of modern artificial light guide lines is from -40 to +85 C with an optical loss of 0.2 dB/m. A bend with a radius of 25 mm is allowed. At a bend radius of 15 mm there is a slight increase in attenuation. For more information on AMP MOST system connectors, please visit tycoelectronics.com and contact the Technical Advisory Center, amp@pit.spb.ru.

Literature

1. 1. Ch. Thiel, R. Konig: Media Oriented Systems Transport (MOST) ein Standard fur Multimedia Networking im Fahrzeug; Tagung Elektronik im Kraftfahrzeug 1998, VDI-Bericht 1415, VDI-Verlag, Dusseldorf 1998.
2. 2. D.Schramm: Lichtwellenleiter- Erfahrungen und Potentiale/ Tagung Forschritt und Zukunft der Automobiltechnik; Verlag Moderne Lndustrie, Stuttgart 1999.
3. 3. W. Heckel, S. Schroder: Kunststofflichtwellenleiter fur optische Ubertagungssysteme im Automobil; Vde-Fachberict Kontaktverhalten und Schalten, VDE-Verlag, Berlin, Offenbach 1999.
4. 4. A. Engel, D. Schramm: Optisches Bussystem fur automobile Netzwerke: F@M Special, 7-8/2000, s 53-56, Carl Hanser Verlag, Munchen.

Author: Petrakov Valery; Publication: radioradar.net

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