Automobile Digital Odometers

Both our family cars have digital odometers and today my curious mind wondered what devices are used for memory storage.

If they need to be continuously powered, what keeps them going when the car battery is dead or removed, and for how long will that auxillary power hold up.

Thanks guys,

Jeff

Jeffry Wisnia (W1BSV + Brass Rat '57 EE) The speed of light is 1.8*10^12 furlongs per fortnight.

Dunno.

Flash memory (probably with load leveling), RAM backed up with a 'supercap', a Lithium coin cell and to hell with you if you own the car more than a few years.

I suppose you could make it mechanical with absolute position readout on each wheel, if you wanted to be perverse.

My Ford is mechanical.

jeff_wisnia wrote in news:r4mdnUut3d460WfUnZ2dnUVZ snipped-for-privacy@giganews.com:

flash memory,just like the thumb drives so common now. They don't need batteries or power to hold their data.

And an inch is close to 1 atto Parsec.

I would expect it uses flash and something like the AES encryption for anti-tamper measures typical of the Mifare cards (which have incidentally been cracked). Many modern cars store a heck of a lot of other info about running and service dates and of course have a black box cyclic buffer inside the airbags. Flash memory is cheap and highly reliable now.

I was surprised to see how fast SSDs are now gaining ground in portable PCs. With no moving parts they tolerate much harder knocks and are lower power. It has pushed the price down a lot as they become more nearly mass market.

Last two cars have been all digital readout. The previous one had a much more sensible fuel economy readout though. The recent improvements are worse. At least the needle can't drop off with solid state readout.

Regards, Martin Brown