It seem strange that in this day of glitter with consumer electronics that quietly chugging along in the back ground is automotive electronics. Todays cars typically contain more than 100Kg of electronics, close to 2Km of wiring and up to 50 or more embedded processors.To operate these processors , cars contain more than one million line of computer code. Complex electronics containing large numbers of 8-, 16-, or 32- bit microcontrollers. Increasingly, automotive electronics are made up subsystems connected through a shared, 'safety critical' communication network, separated by gateway controllers......... Make you think what happens when it don't work!!

As a member of the RSGB (Radio Society of Great Britain) I was reading a feature in RadCom (RSGB Magazine) about GPS and how its works, and as so many cars are using this technogy I would include it in as general information in my technical topics page. So with very little editing here goes. The global Positioning Satellite system is designed to allows a user anywhere on (or above) the earth's surface to determine his position to an accuracy of a few metres. It does this by maintaining a constellation of satellites in very accurately-determined orbits, such that at least four are visible from any location at one time. Each satellite transmits a spread -spectrum code so that observers are able to determine the time of flight of the signal, and hence their distance, from each satellite observed. Once these distances are know, trigonometry and triangulation allows the observer's position to be calculated.In order that the exact distance from each can be determined, the satellites have to be locked together in time. To ensure this, each satellite carries a caesium frequency standard (plus a rubidium one, and crystal oscillators, asback-up in the event of failure). So each and every satellite nows transmits a code to the ground that allows the exact time to be determined. To measure distance accurately to a few metres, timing accuracy has to of the order of nanoseconds (3ns f 1 metre of signal travel in free space). Any GPS receiver locks to the codes, measures the time-of-arrival difference and calculates the distances to its location from each satellite, determining the user's location. I should add that if you would like further information about the RSGB  link to www.rsgb.org