Citroën Pioneered the Use of Fiber Optics in Automobiles

Did you know that Citroën used fibre optic cables in DS models from 1972 – 1975? At the time, optical fibers were hardly known to the general public except for decorative lighting. Citroën was first in the automotive industry to find a practical and very useful application for them.

Citroën utilized plastic optical fiber (POF) to send light from the dashboard cluster to the illuminate the keyhole for ignition switch. The other end of the fiber optic cable plugged into the back of the gauge cluster.

Photos — Chris DuBuque.

It’s odd that Citroën did not decide to use fiber optic cables for the same purpose in the SM at the time. When you leave the door of the SM open for an extended period of time, the light-bulb in the steering column cover gets quite hot and in a few cases has melted the the ignition switch surroundings! 

Today, optical fiber transmits far more than illumination. It is used to covey data information to all our onboard screens. We didn’t see optical fiber used by other manufacturers until 1998 with Mercedes and then others followed. Dual bus fiber optic networks were developed for cars to transmit audio, video, voice, and data signals. In 2001 Byteflight, an automotive databus, was developed by BMW in partnership with Motorola, Elmos Semiconductor and Infineon, (it was first introduced on the BMW 7 Series) and then it evolved to become the more powerful MOST (media-oriented systems transport).

Modern buses utilize both parallel and serial communication, employing advanced encoding methods to maximize speed and efficiency. Features such as direct memory access (DMA) further enhance performance by allowing data transfers directly between devices and memory without requiring CPU intervention.

In modern vehicles, several automotive databus systems are employed, each serving specific purposes. Here’s a breakdown of the two most prevalent ones:

CAN (Controller Area Network):

• This is arguably the most widespread databus system.
• It’s used for communication between various electronic control units (ECUs) within a vehicle.
• CAN is reliable, robust, and cost-effective, making it suitable for numerous applications, from engine management to body control.  

LIN (Local Interconnect Network):

• LIN is a lower-cost serial communication system used for less complex applications.
• It’s often employed for communication with sensors and actuators in areas like door controls, window lifts, and lighting.