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I (a newb) would like to design a small & simple GPS tracking system for my 2 cats

Discussion in 'General Electronics Discussion' started by hedgehog90, Sep 1, 2012.

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  1. hedgehog90


    Sep 1, 2012

    First let me tell you about myself. Just at the mere sight of the first line you can probably tell already that I am not an electronics expert by any stretch of the imagination, I am a newb.
    However - I did receive an A in my Electronics A Levels, but that is not a valid indicator of my true knowledge of electronics.
    Ironically, I don't understand some of the most basic things. Grounding. What diodes really do. AC / DC (although I am aware of the famous rock group of the same name)
    For my electronics A level coursework I designed a scrolling sign made up of 6 or so starburst LED displays. I programmed a chip to say something like "I LIKE ELECTRONICS". Completed in a day. Got me an A.


    Also, my professional job is as a game designer. I write lots of code, and I have a very good understand of all things code-like.

    Now, here is the problem that I want to solve:

    We have 2 cats, Tig and Ollie. We live in quite a nice rural area, but unfortunately, we've lost 2 cats to the road and the lane near us.
    It causes us a great deal of stress just letting Tig and Ollie out for 2 hours every day. So, we bought a loc8tor and several tags to track them. It's a simple device. the tags emit a pulse, the loc8tor shows you the signal strength from 0-100. It claims to work with tags up to 600 feet away (with no obstructions it's more like 400 feet, but you expect it)
    I've looked inside the tags and the handheld loc8tor, and it looks pretty simple. Certainly not worth the £80 we paid for it.

    Here's some stuff to read:

    Anyway, for the past few days, we've been finding Tig alarmingly close to the road, and while he spooks at the sight of an unrecognised visitor in the house, he looks pretty mellow while cars and massive lorries race past him at 60 mph...
    Because the road is so far away, we can't get a signal of him without running around the garden and the nearest field for quarter of an hour. It's a pain.

    Before we bought the overpriced loc8tor, we looked around for something similar but with GPS instead of RF.
    Such devices exist, but they were enormous... I found a lot of pictures online of very perturbed cats with heavy weights wrapped around their neck. Also, the GPS tracking came with a monthly charge...


    So today I looked around online for info on GPS chips. I have an android phone with GPS, how big can they be I wondered. Well, they're tiny.
    Finally I got round to thinking that maybe I could build some sort of cat tracking device myself with minimal cost?
    I like opening stuff up and having a poke around. I fixed (and then broke) a PS3 by taking it apart. I'm quite good with my hands.

    I understand this might sound like a naive, over-confident thing for such a electro-newb to say, but ideally, I want to create a deice, no bigger than a loc8tor tag (30.5mm x 19.5mm x 8.5mm) that will regularly inform me of it's exact position on the globe (ie - in the field next door most likely) via my phone or computer.

    Now, I had a bit of a think and realised there's a problem here, apart from the task itself.
    Your normal GPS (the GPS in the car, the GPS in your phone) works like so (I'm assuming):
    GPS requests position -> Satellite receives request, calculates, sends response to GPS -> GPS receives response and displays.
    But for my supposed device it would be:
    GPS requests position -> Satellite receives request, calculates, sends response to my phone's GPS -> Phone receives response and displays.

    Also, can you just buy the core mechanics of a GPS and have it request and receive with just any satellite? I expect there are permissions and restrictions that need to be gotten past.

    As I'm writing this I'm realising more and more that what I want seems like I will unlikely be able to make such a thing on my own... But having said that, in the last couple weeks I was called upon to design a call management system for a friend who runs a small call centre, and as difficult as it was, I was able to do it.
    The same is true when I started making games. It looked incredibly difficult and I felt it was impossible, but it didn't take long for me to get a grasp of it all.

    If I put my mind to it and do the research, I feel like I should be able to do this as long as I have the necessary tool and help.

    So, to clarify, I would like to design 2 small tags, likely running off 2 small 1.5V batteries, that will get it's position via GPS and send it to my phone/computer, with the ability to be switched on and off. Sealed withing a plastic container that I can then attach to my cats' collar.
    Is this feasible?
    If so, I would like very clear instructions on how to do so.

    I apologise for the length of the thread and the amount of unnecessary info.
    Last edited: Sep 1, 2012
  2. davenn

    davenn Moderator

    Sep 5, 2009
    hi there
    welcome to the forums

    from you...
    NO, the GPS satellites receives nothing from the ground based GPS systems in your car etc. The GPS system is a transmit from the satellite only. your GPS receiver just receives signals from a bunch of satellites and triangulates your location, altitude and ground speed. A minimum of 3 satellites are needed for a rought location, more satellites above your local horizon improve the accuracy.

    You would need to be able to receive the GPS signals, decode them, they use a standard NEMA string of data take that data and feed it into a transmitter to be received by you in the house. That is a pretty complex project. to receive it on your mobile phone, you would need a mobile phone and the other receiver and decoder electronics on the cat along with the weight of battery power supplies to keep it running or the hours or days that the cats were out and about. The mobile phone on the cat needs to be able to call your mobile and transfer that info using some sort of apps that would have to be coded ( not my field)
    It now looming into a serious and costly project if your are wanting the mobile phones to be contineously active in relaying the data

    reread the above comments on how the GSP satellite system works

    Last edited: Sep 1, 2012
  3. duke37


    Jan 9, 2011
    I would not know how to do this, however, GPS is a one way system, there is no way of sending requests or data to the satellites.

    You could perhaps get a transmitter working in the 400MHz region to send the data to a receiver. If the transmitter was activated for a second every minute, the battery consumption may be reasonable.
  4. BobK


    Jan 5, 2010
  5. hedgehog90


    Sep 1, 2012
    Okay, I understand how GPS works now.
    Of course, the power required to send a signal that will reach an orbiting satellite would not be possible with a phone or TomTom... I should have just quickly googled that before posting.

    So, in that case, I can't think of any reasonable way that I can transmit the position of the tag to my phone/computer...
    The way other GPS collars transmit to your phone/computer must be by using mobile networks.
    That's why there is a monthly cost I imagine.


    If GPS is out of the question, building a stronger RF transmitter might be helpful... but not as helpful as a GPS tracker.

    Any ideas?

    Thanks for the replies.
  6. donkey


    Feb 26, 2011
    ok if you want a already made item that will use gps to track your cat and you then log in via your computer to find their location you can get a smartphone with gps of ebay. An Iphone for example has the site "wheres my iphone" and you simply log in and find your phone. finding a light weight phone that is cheap is not the big issue here though as alot of people upgrade slowly and get rid of their old phones for cheap. the issue here is as you said, weight. and then you have to attach it so it doesn't fall of. then there is also the cost of keeping that phone on a sevice plan to be able to log in and locate it.

    If you want an unreliable source that uses both rf and gps you can try another approach. (coca cola I am hoping you can find me the pic alternatives lol). Arduino is a very very very very basic microcontroller setup that has many "shields" or attachments. on of which is gps and another is radio trancievers. these will simply plug in. The big issue is programming. I can think of a simple approach that will help using the gps to get data, arduino to calculate position then the tranciever to broadcast position to a reciever somewhere.
    this approach may be bulky to start with and you will not get exact position constantly or you will drain your battery fast. but you could hook it up this way.

    there are a heap of options available but maybe the simplest is get a boundary system happening and when the cats go to that side of the yard their collar emits a smell or liquid to make them scared of going there.
  7. hedgehog90


    Sep 1, 2012
    Ok, I've had an idea.

    So, the problem is, my locating device and tags are not strong enough and not accurate enough.
    Our house is situated between 2 fields. There are many trees in the hedgerows.
    I would need to buy/build several radio transmitter/receivers, which I can attach to the cat's collar and to trees surrounding the fields (the higher the better).
    Each transmitter/receiver will need to detect signals from either cat and from neighbouring transmitter/receivers.
    And, here's another clever idea - I have an FM receiver on my Android phone. So, I could program an app to detect incoming signals from the nodes, and based on number of signals, their locations and the signal strength, I can estimate on my little app their position on a map, and using my phone's gps, I can also see where I am.
    When I get close enough to the cat to receive their tag's signal on my phone (again - if that is possible to use the phone's firmware-based FM receiver for such a task), then I can use the strength of the signal and my own location (using the phone's GPS) to work out more accurately where the pesky blighters are.
    If the cat's are not detected by the receivers, then give me an alert on my phone.
    I don't need gps for the cat's collar for this, but I guess it could be added to make it even more helpful.


    How would I do any of this? I HAVEN'T THE FOGGIEST!
    I have some experience in programming microcontrollers, and I have tried my hand at android apps before, but if you gave me all the ingredients for this, I'll still be left scratching my head.

    It would require building a set of programmable receiver/transmitters, connected to replaceable power sources (with some luck though they should last a while, considering my cat's loc8tor tags last months on just 2 tiny 1.5V batteries), programming them so that they send out a signal with the cat's location and signal strength, and then using that data via my phone's FM receiver and my phone's GPS, display the presumed radius of the cat's possible location on an aerial map, along with my exact position.

    Could someone please tell me if this is a feasible idea, and if so, please tell me what components and tools I'd require, and finally how I would build one of these receiver/transmitter things.


    Edit: Hmm, after a little research I doubt I will be able to use my phone as a radio receiver. While it can pick up a range of FM signals, it probably won't pick up the frequency I'll be hoping to broadcast

    Edit: I found this:
    So there is some hope with the android acting as the main receiver/display unit.
    Last edited: Sep 5, 2012

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    Can't add anything to the GPS issue that hasn't been said but I'd like to say that's a very pretty kitty. ;)
  9. davenn

    davenn Moderator

    Sep 5, 2009
    hi hedgehog

    to be honest, this is a really complex project, and you need to come to understand that. Regardless of what system is used its not something that is going to be designed or build quickly within an affordable budget of the avg person.
    It would be doubtful that you would find some one willing to design or build it without many $1000's of money out front.

    If you cant find something out there that is aready available "off the shelf" then the project wouldnt really likely to be feasable

  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    I can't add much here; everyone else has made good suggestions and given good information.

    My approach (and I think it's already been suggested here) would be to get a small, light GPS receiver module, like the ones used in smartphones, and a tiny radio transmitter using an unlicensed frequency band with frequency modulation and a simple data modem, and a microcontroller to interface between them. The GPS receiver needs to be powered all the time, but the transmitter only needs to be powered when it's transmitting. Every 20 seconds or so, the microcontroller would query the GPS receiver for its current position, and transmit a small block of data that would be received by an FM receiver in your house and decoded by a dumb modem into a serial data stream, which you could acquire through a serial port, USB serial IC, etc, or display on an LCD.

    Another thing comes to mind. Your cats probably aren't afraid of cars because they have no idea how dangerous they are. If you could give them a fright without hurting them, and associate it in their mind with vehicles, they might learn to be afraid of them. Perhaps drive past them in a vehicle and throw something towards them that makes a loud crashing sound when it lands? Cats hate loud crashing sounds (knock over a pile of saucepans near them, you'll see what I mean). I'm not advocating cruelty to cats - I love cats. But you need to make them scared, without actually hurting them.

    Good luck!
  11. wingnut


    Aug 9, 2012
    Could one not use the signal from the original loc8tor so that when the cat gets too far, and the signal becomes zero, this activates a piezo buzzer around the cats neck to frighten him - or at least make it easy to hear where he is - like an electronic bell.

    Or, buy a cheap radio/remote controlled car and take out its receiver which is small and has limited range. Put this with a piezo buzzer set by default to buzz around the cat's neck. Thus when the cat wanders out of range and loses signal, the buzzer activates.
    Last edited: Sep 6, 2012
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    What you're describing is opposite of his system. He holds the receiver while the cat carries the transmitter. That said, yours might be a better system. Condition the cat to know that relief from the annoyance is simply a matter of not going any further. This is similar to the way electric shock collars work,

  13. thebluepuppy


    Sep 7, 2012
    what i would reccomend is to try and build it. something that might be cheaper is get laser trip that goes around all your doors and get a little keychain device that when it goes off your keychain is activated and starts pulsating and beeping and flashing. that way when you go to sleep if kitty trys to sneak out your keychain will alert you. plus its cheaper then a security system
  14. hedgehog90


    Sep 1, 2012
    For now, let's make this simple:
    Lets suppose I want to make a tag for 1 of my cats consisting of a transmitter (and possibly a receiver too, to tell the transmitter when to start transmitting which would be much more efficient), and a receiver attached to an arduino attached to my phone, RF at 433MHz with a range of 300m. And consider that the cat's tag is operating off 2 LR44 1.5V batteries.

    Can I make anything small enough that will send a dumb signal to my arduino-receiver-phone thing?
    The cat's transmitter only need to broadcast their ID, Ollie or Tiggy.

    The receiver attached to my phone should pick up the signal when within 300m, and then it needs to very basically decode the signal for the ID and get the signal strength.

    I understand that this won't be directional like the Loc8tor, but with atleast 3 nodes it will be quite accurate in telling me their position.

    Anyway, for now, let's just imagine that this is all I want to do. 1 transmitter, 1 receiver.
    What would I need to build this, and how would I build this. Please be detailed.

    I appreciate all the other suggestions and all of your help, but I really just want to know how I would do this exactly. It can be improved upon later.
  15. hedgehog90


    Sep 1, 2012
    I've ordered some basic stuff from ebay:
    Some pcb stripboards
    A better soldering iron
    5 x PIC12F683-I/P
    PIC Programmer

    I haven't got an arduino and I haven't bought any components (apart from the PICs), because at this point that would be silly.

    I've been looking around for tranceivers, and I would guess that the TRM-433-LT will do the job best. It's very small, efficient and apparently easy to operate. It boasts and incredible range, almost 1km.

    If that's no lie, I'd be interested in getting a GPS to work with it.
    That way, I only need 3 transceivers (2 for each cat, 1 for me), 2 GPS modules & 1 arduino. Relatively simple.

    All I need is some more advice and a helpful hand to take me through the process of putting it together.
    I will be chuffed to bits if I can make something better than the Loc8tor :)
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