Thread: GPS vehicle tracking, any advise ?

i will then enter the data manually into my gps software on my pc that will show me the current location

Isnt possible to rip the text message from the phone via software with datacable...and then into the GPS software? Perhaps process it again as if its is like a $GRPMC sentence and then output it to a virtual com port? This should ensure better compatibilty. Problem is if this is used for live tracking then the tracking phone need to constantly text the phone...the tracking phone will run out of credit.


A clever thief not many of them about, but if there was one who deceided he would be clever and locked u your car up in a garage no GPS signals

The GPS should still be able to transmit the last known position...so you should be able to find if the car is locked in the garage...unless of course the car is put in a truck and moved somewhere else.

i can use DTMF tones using a decoder circuit to control the system and to request functions via a simple dtmf tones hey theres 16 avliable and only 12 keys on a keypad so i may use a pic to accept a unique code for access and allow infinite outputs via dtmf say "23#"

Why not use your phone to text the tracking phone to turn on/off a device? At least you dont have to carry a DTMF tone generator.

Of course all this need to be controlled by a MCU.

Heres a basic block diagram of my project and I hope its not too complicated for some.

I have done the PIC program and its under test on PIC16F627 will be upgrading it to PIC16F648 for more memory.

The idea is to use a normal phone (pay-as-you-go with no credit). Im using a nokia 3310 for my test. I wanted to stick to normal phone that most poeple should have laying around. It is still rare to find a spare phone with real hardware modem...most either dont have one or just use a software based modem.

Anyway heres a quick rundown of my progress. The GPS 4800 baud NMEA sentences are fed to the controller, the controller ignore all the sentences apart from $GPRMC. This $GPRMC is then stored in the PIC internal buffer. This is then read internally and retransmitted through the FSK modulator at 300 baud. The FSK is generated by the PIC hardware PWM module, through a filter before being fed to the mobile mic input.

The frequency of the FSK is 1200/2400Hz, which work fine when passed through the phone digital network. It is important to slow down the transmission rate from 4800 to 300 baud due to the way the voice is compressed and decoded in the mobile phone.

On calling the tracking phone, the receiving phone should then output the 300 baud FSK signal. This can be from a landline phone directly outputing the signal to the controller via the phone audio out, the mobile phone audio out or through a phone pickup device.

Another PIC is programmed to detect the 1200/2400Hz tone as a '1' or '0'. This is done throught DFT calculations to determine the presence of the 2 tones. The decoded output is then reshaped, decoded and stored in the buffer. The buffer is then read by the 4800 baud transmitter and out to the PC comport. The same $GPRMC sentence is always transmitted until a new one is available...the update happen once every 2 seconds.

At this moment Im able to read the GPS NMEA and transmit the $GPRMC at 300 baud FSK. I have tested it from mobile to landline all seems to work fine. The FSK signal is received via a pickup device attached to a land line phone "BT diverse 4010" then into the PIC. The PIC can decode the signal very well which is then fed to the PC comport.

I have got the hardware FSK decoder working...but however it is possible to write a windows software that can decode the FSK signal and then output it to a virtual comport. The FSK signal from the phone is fed into the line-in of the soundcard. The software then analyse the signal, looking for 1200/2400 tones and regenerate the '1's and '0's on the virtual comport. A program called TRUETTY can do just this.

I dont have enough knowledge about programming such application. This software based decoder will elimate the hardware based decoder and therefore even cheaper solution can be made. About £5-10 add-on will turn your spare mobile phone into a tracking device.

I think it should be fairly straight forward for an experienced programmer to program an all software FSK decoder...all thats needed are :

1) The 300 baud FSK signal from the phone is read by the soundcard line-in or mic.
2) The software then analyse this FSK signal and decodes the data in real time.
3) The decoded data is then outputed to a virtual comport at 4800 baud.

Well I hope someone can help me out with this one

At the moment Im still putting all this together. Im soon hoping to control the mobile phone with the PIC via the data cable...this should allow me to text if the car need attentions.

making sure that text has arrived safely sometimes a big delay can take place

Thats true.


also i would need to purchase a RS232 gsm modem that allows for the sms data to be extracted via AT cmds, having it dtmf controlled will let any phone be used that supports dtmf most mobiles do and so do tone dialing type telephones.

I thought you gonna use text to transmit the coordination? In that case you be needing a data cable anyway? so the PIC can control the tracking phone.

I dont think a modem is needed just for texting and receiving text...Im almost sure sending and receiving info from the phone can be done just via datacable or infared.

I may be wrong as I havent got as far as controlling the phone through the data cable. This is what I wanted to do soon...the PIC can answer the tracking phone, hang up the phone, send a text message to another phone and extract the text message from the phone. If you can confirm this is not possible without a modem then my plan would change. I should atleast be able to put the tracking phone on autoanswer so whenever I call it it will start to transmit the cordination by mean of FSK tones...well I cant see any autoanswer option on my test phone anyway


As for cost like you say if you have an old mobile phone lying around that be perfect for the dtmf side of things as for actually trasnmitting hte NMEA data it would need to be capable of GPRS for web update or SMS compatible for text update

Thats the whole thing why I decided to make my own 300 baud modem programmed into the PIC. The NMEA sentences is transmitted by tones of 1200Hz and 2400Hz through the mic input of a basic phone. I originally wanted to design a 4800 baud modem but then had to drop down to 300 baud due to the way the voice are being compressed when passed into a mobile phone. Since I couldnt get the 300 baud to work properly I gone even lower after reading alot of info on the net, some say its just not possible to transmit 300 baud through a mobile phone without a built in modem due to limited audio bandwidth and compression used. I know DTMF tone can pass through the phone without a problem. So in turn I made a DTMF modem, each DTMF tone is used to transmitt a nibble, a pair would make a byte. I abadoned the idea as I can only get 5 characters per second out of it, not exactly good for live tracking. Anyway after a few more hardwork I finally got the 300 baud modem working reliably...and Im gonna stick to it

If you read my previous post, I know its long but I did explain how to even reduce the cost by using a software based decoder...may aim is to turn any old crappy phone into a cheap but effective tracking device

Anyway thats my part.






How far have you gone into your project?


This is something you may wanna see :

GSM-SMS tracker project

Dont know if you seen it, but I think its similar to what you are planning to achieve.
The idea didnt appeal much to me as it does say you must use a phone with a built in hardware modem...Im sure it did