Half a croissant, on a plate, with a sign in front of it saying '50c'
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Or, how to never lose your car in a multistorey carpark again
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I'd love a radio direction finder car tracking system. OK, I'm absent-minded enough to lose my car in car parks on a semiregular basis. This idea would help me find my car again!

What you have is three class 1 Bluetooth modules, so a theoretical 100m range as I understand. The exact tech isn't important, Bluetooth merely seems possible. Modules are sold together and share serial numbers so the system can still operate if more than one person has it per carpark.

Modules 1 and 2 sit at opposite ends of the car and share a clock - either they're wired together or one has a clock and the other reads the time from it. For a retrofit, that seems more practical. This clock will need at least millisecond accuracy.

Module 3 is on your keyring and has a small buzzer and a button. Pressing the button sets the module to seek. If it can't get a response from either module, you're out of range. If it can, it checks the time with both modules. It then beeps every second for as long as you hold the button in with the pitch of the beep indicating the difference in time received from the two modules.

I know 2 alone isn't normally enough to get a position, so I'd envisage the user sweeping their keys to gain an initial direction. From then on, it should be enough. 3 transmitters begs the question of where to put the third transmitter...

eftpotrm, Dec 30 2004


       take a can of spray paint and write the floor number and area in big letters in the lobby as you leave
benfrost, Dec 30 2004

       take a can of spray paint and write the floor number and area in big letters on your car door as you leave
phundug, Dec 30 2004


       Could actually work unlike Polocator, has no graffiti (and so consequently scales) and should do nothing whatsoever if you're on the wrong floor so would be somewhat useful in a multistorey carpark.   

       And if you can whistle loud enough to activate this reliably when you can't actually see the car, you are either a public health hazard through volume or you shouldn't be driving :-)
eftpotrm, Dec 30 2004

       Assuming an SUV that is 5 meters long, the difference in travel time for the clock signals to your keychain is at most 16 nanoseconds. (And could be considerably shorter, for instance if you are directly to one side of the vehicle). You'd need atomic clocks in the vehicle and your keychain to get that kind of accuracy.   

       That would either make this "bad science" or the most expensive car accessory ever made.   

       Or did I miss something?
krelnik, Dec 30 2004

       The Cesium option.
bristolz, Dec 30 2004


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