SparkFun Forums

[bglasner]

I'm currently working on a project to put a gps chip on a keychain to track keys if they are lost, but I don't have a lot of experience with gps and would appreciate some outside expertise.

We want to be able to use a smartphone to track the position of the keychain, but we are wondering if it is even possible for the receiver on the keys to send that information to the phone. Basically can the chip be tracked externally, or are the gps coordinates only useful for the keychain to locate itself (if that makes any sense)?

We've also been trying to do research on which components we need in this system, but so far the only information we've found is how the receiver communicates with the satellites to determine its location. We don't really understand how the receiver then decodes that information or how it transmits that information in a way that is meaningful to a user.

We assume we need a receiver obviously, and also an antennae and some kind of power source, but what other components might we need? Would we require some kind of onboard microcontroller to carry out other functions?

Any help you guys would be able to give on this project would be greatly appreciated, and thanks for your time.

[michelebavaro]

Hello bglasner,

A preliminary question: is GPS really necessary for a key tracker?
Do you really need to find your keys kilometres away (or on the other side of the World)?

If is enough to have a simple proximity device
then woulnd't BLE (Bluetooth Low Energy) be a more suitable solution?
The fact that it's easily integrated with recent smartphones seems to have better market perspective too, right?

I welcome your comments.

Cheers,
Mic

[fll-freak]

If you were to implement this as stated, you would need a GPS receiver, its GPS antenna (often incorporated into the unit), something to receive the GPS location strings (search NMEA), something to broadcast those strings to something else, something else that would pick them up, and of course a battery. Some people use cell phone modules to send text messages, others use wireless radio.

With today's technology, all that is not going to fit into a keyfob, unless you like plum sized keyfobs.

But the biggest problem I see is that your keys are often lost indoors. GPS systems do not do very well indoors. Unless you are using a very good (and large antenna) or you are operating next to a window than GPS will not pick up satellites and not report a position.

Ever hear of "clap-on clap-off"?

[bglasner]

Thanks for both of your guys' feedback.

Mic, I understand what you are saying about needing to find your keys at such long distances; it seems unnecessary. Our original idea was to use an RFID tag for short range tracking, but when we began researching RFIDs we found that very few of them can transmit at ranges greater than 2-3 feet, so this wouldn't be a very great tracking device. The reason we moved on to GPS was that we wanted to try and see if we could sort of integrate a long and short range tracking system where we would use the GPS to track your keys up to a certain level or precision if maybe you dropped them at the park or something, and then once at shorter range send out a radio signal that would turn on a beeper on the keyfob so that you locate the object.

We don't have a lot of experience with how GPS works or the individual components, so that's why we came here to find out if this idea was possible or even worth pursuing, but after what fll-freak said about the necessary components, it doesn't seem like a particularly user friendly system.

I am definitely interested learning more about the BLE technology you mentioned Mic. One of the ideas we considered was playing a sort of 'hot and cold' game with the object so proximity tracking would be a potential solution for us. I'm just curious, how would this system be different than RFIDs?

I appreciate all of your help
Thanks again

[fll-freak]

Don't want to totally scare you away from GPS, but it is not often what people seem to think. This magic system that has pin point precision any where in the world inside or outside. In fact today, at my location, there was a 15 minute period of time when not enough satellites were visible to get a semi accurate 3D GPS fix. That was with a high gain antenna outdoors with a clear view of the sky. God help the person that thinks their cell phone GPS is going to give them a fix when they have a medical emergency in a metal building.

Now if you can live with those limits, than a GPS module can be about the size of a large stamp. The processor your would need could be as small as a penny think slice from a keyboard key. You are now left with power and a transmitter of some sort. Lots of technologies to look into. Bluetooth, GSM, Xbee, ZigBee, and various proprietary systems. Here range will dictate size and power consumption.

Now you need to consider the receiver! Do you have a dedicated device, or are you limited to what is in your average smart phone? And what happens if in your drunken stupor you misplace your keys and your phone?!

[michelebavaro]

Hello bglasner,

Well apart from the obvious and authoritative Wikipedia page:
http://en.wikipedia.org/wiki/Bluetooth_ ... n_profiles

There are a lot of Companies selling BLE modules but the one I like most is a Company of bright people in USA:
http://www.blueradios.com/hardware_LE4.0-S2.htm

The reason why I prefer them over other manufacturers is that whenever
I contacted them with enquiries they replied shortly,
but sharply catching my idea and bringing my vision one step forward.
(Please note that I have nothing to do with Blueradios... I am an independent consultant).

When you look at their nBlue, you will see that like many others is based on the CC2540/1 SoC from TI:
http://www.ti.com/product/cc2540

Most manufacturers use that very same chip, but Nordic is also catching up:
http://www.nordicsemi.com/eng/Products/ ... low-energy

and see especially:
http://www.nordicsemi.com/eng/Products/ ... gy/nRF8002
(Bluetooth low energy proximity IC)
http://www.nordicsemi.com/eng/Products/ ... S-Demo-App

Other useful links might follow:
http://www.youtube.com/watch?v=Vy0jFWpAO2Q&t=4m25s
http://www.youtube.com/watch?v=TUwedeshPJU

Hope this helps.

All the best,
Michele

[MichaelN]

As has been noted, a huge problem with GPS is reception indoors. AFAIK, most cellular carriers in the US use triangulation from base stations to achieve the mandated location tracking provisions of "enhanced 911" for this very reason.

With today's technology, all that is not going to fit into a keyfob, unless you like plum sized keyfobs

...a GPS module can be about the size of a large stamp.

Actually, the GPS module and antenna can be quite tiny (much smaller than a postage stamp these days).

You are now left with power and a transmitter of some sort.

The transmitter could be quite tiny too (there are plently of single-chip solutions available from vendors such as Atmel, TI, Nordic etc).

However, power management (and the resulting battery) is a big issue. GPS modules still use a relatively large amount of power when you're talking about running something for an extended period on battery power. You would need to implement a system where the module only tries to get a fix periodically, or maybe you could use a transceiver for communication instead so it only tries to get a fix when commanded to do so. In the latter case, you'd also need to have tight power management on the transceiver, as they tend to be power hungry when in receive mode (perhaps you would command it to wake up for a few tens of milliseconds every few seconds).

After all that, as Skye originally pointed out, there are already solutions that listen for a noise (clap or whistle), and then advise you. There are also solutions that use RF to command the keyfob to emit sound / light, such as this:
http://www.keyringer.com/

[MichaelN]

GPS modules still use a relatively large amount of power when you're talking about running something for an extended period on battery power. You would need to implement a system where the module only tries to get a fix periodically...

Thinking about this more, I think a better solution (if you do use GPS) would be to fit a movement sensor so that the unit doesn't bother trying to get a fix unless it has moved. There are some very low-power accelerometers these days that provide interrupts when they detect movement. This way, you only need to have a transmitter on the keyfob, which saves on power.

[bglasner]

Thanks for all the advice. We think we are going to look into the BLE since it would seem integrating a GPS would be unnecessarily complicated for the scope of this project.

I appreciate all of your guys' help!