city link proximity detectors- how do they work?

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Heywood Jablome - 29 Nov 2004 01:48 GMT

I have lately been interested in proximity detector technology. I see that
the USB devices that lock your computer if you are greater than 2m away are
becoming relatively cheap, but their battery life of the transmitter is only
a stated 2000 hours (I'm guessing less). That means that you need to change
the battery every two months. After all they operate on 433mhz and have to
transmit intermittently all the time.

The new petrol electric Toyota Prius has an option for a proximity key,
which opens the central locking if you are within a short distance from the
car. Thats a nice feature when your hands are filled with shopping -etc, but
their website has no info on what this technology is based on, so I dont
know whether the transmitter has a battery in it at all.

The city link car detectors in victoria do have a battery inside, but they
seem to last a few years. Does anyone know what technology they are using?

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David L. Jones - 29 Nov 2004 02:44 GMT

> I have lately been interested in proximity detector technology. I see that
> the USB devices that lock your computer if you are greater than 2m away are
[quoted text clipped - 8 lines]
> their website has no info on what this technology is based on, so I dont
> know whether the transmitter has a battery in it at all.

If a device does not have a battery then it's most likely using RFID
technology.

Dave :)

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dmm - 29 Nov 2004 21:31 GMT

>If a device does not have a battery then it's most likely using RFID
>technology.
>
>Dave :)

Congratulations Dave on getting a Distinctive Excellence Award for your Battery sAVR design
in the Circuit Cellar AVR contest..

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Michelle Vadeboncoeur - 29 Nov 2004 21:00 GMT

> I have lately been interested in proximity detector technology. I see that
> the USB devices that lock your computer if you are greater than 2m away are
[quoted text clipped - 11 lines]
> The city link car detectors in victoria do have a battery inside, but they
> seem to last a few years. Does anyone know what technology they are using?

For the Smart Entry and Smart Start (SE&SS), aka Smart Key,
there is a flash demo of it here:
http://www.toyota.com/vehicles/2005/prius/key_features/smart_entry.html
(the doors do not automatically unlock when you're nearby, you still
have to touch the handle to trigger the unlock)
(True, there's not much info on the toyota.com.au site about the Smart
Key: http://prius.toyota.com.au/Prius03/Portal/Article/0,1225,191-254-6231,00.html
...)

Yes, there is a battery inside of the keyfob, which is mostly there if
you need to press the lock/unlock or Panic buttons, but it is also
required for the Smart Key system to recognize the fob at range. (If
the fob battery goes dead (uses a calculator/watch battery), you can
still use the dash slot which uses a passive system to identify the
fob
(which is what people without a Prius package that comes with the
Smart
Key do normally).

IIRC the keyfob uses RFID.

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Electronics Forum / Electronics / November 2004

city link proximity detectors- how do they work?