MP3Car.com - View Single Post

Ricky327 · 05-17-2004, 07:06 AM

all you have to do is use the cell phone headset plug to input the audio output from the tinytrak, and then set the prepaid cell on autoanswer.

Problem is...as been said the tinytrak cant work with mobile phones. It look like the bandwidth of the phone audio is too narrow to work with 4800 baud rate. I read on the net somewhere that the maximum frequency the mobile phone can handle is only up to 5KHz...not sure about the lower limit.

I was thinking :

A PIC is programmed to take in the 4800 baud rate from the GPS. Since most GPS unit repeat itself once every second, the PIC will take in 1 second worth of data. The data is then stored temporarily and then retransmitted as tone throught the micophone input of the phone at a lower baud rate, 110 perhaps? whatever the maximum the phone can handle.

The receiving end decode the tones then reconvert the 110 back to standard 4800 bauds for the PC to plot the locations. The same data are represented again until new one are received, this is done to fill in the missing data to satisfy the 4800 baud rate . In effect the GPS locations is only updated 4800 / 110 = once every 44 seconds...which is still workable to find where your car had gone

So it work something like this :

You ring the tracking phone and it answer automatically. (Set to autoanswer, not sure if this is true for all phones)

Then the unit work as follow :

GPS ---> [4800 to 110 baud translator] ---> [FSK tone generator] --->[Tracking mobile phone]
.
.
.
[Your phone] ---> [FSK decoder]---> [110 to 4800 baud translator]--->[PC]

As can be seen the idea is not to hard to implement using the PIC microcontollers.

The FSK can be done through software or hardware as all it does is generate a different tone for '1' or '0', 1200Hz for '0' and 2400Hz for '1' lets say. The FSK decoder can also be done through software or hardware...software solution is much better for encoder and decoder as this reduce the hardware cost.

Although the GPS update rate is slow but the idea should work with cheap phones, no need for phones with built in modem or it being data enabled. An old pay-as-you-go type of phone with no credit can be used as long as data can be transmitted successfully. The tracking unit is only activated when you ring its number.

A much neater solution is of course to use phones that can be controlled via serial ports. Been checking it last night...so much things can be done to it. The biggest problem is programming the PIC to take advantage all of whats possible with data enabled phones.

05-17-2004, 07:06 AM	#34
Ricky327 Raw Wave Join Date: Jun 2003 Location: London UK Posts: 1,818	all you have to do is use the cell phone headset plug to input the audio output from the tinytrak, and then set the prepaid cell on autoanswer. Problem is...as been said the tinytrak cant work with mobile phones. It look like the bandwidth of the phone audio is too narrow to work with 4800 baud rate. I read on the net somewhere that the maximum frequency the mobile phone can handle is only up to 5KHz...not sure about the lower limit. I was thinking : A PIC is programmed to take in the 4800 baud rate from the GPS. Since most GPS unit repeat itself once every second, the PIC will take in 1 second worth of data. The data is then stored temporarily and then retransmitted as tone throught the micophone input of the phone at a lower baud rate, 110 perhaps? whatever the maximum the phone can handle. The receiving end decode the tones then reconvert the 110 back to standard 4800 bauds for the PC to plot the locations. The same data are represented again until new one are received, this is done to fill in the missing data to satisfy the 4800 baud rate . In effect the GPS locations is only updated 4800 / 110 = once every 44 seconds...which is still workable to find where your car had gone So it work something like this : You ring the tracking phone and it answer automatically. (Set to autoanswer, not sure if this is true for all phones) Then the unit work as follow : GPS ---> [4800 to 110 baud translator] ---> [FSK tone generator] --->[Tracking mobile phone] . . . [Your phone] ---> [FSK decoder]---> [110 to 4800 baud translator]--->[PC] As can be seen the idea is not to hard to implement using the PIC microcontollers. The FSK can be done through software or hardware as all it does is generate a different tone for '1' or '0', 1200Hz for '0' and 2400Hz for '1' lets say. The FSK decoder can also be done through software or hardware...software solution is much better for encoder and decoder as this reduce the hardware cost. Although the GPS update rate is slow but the idea should work with cheap phones, no need for phones with built in modem or it being data enabled. An old pay-as-you-go type of phone with no credit can be used as long as data can be transmitted successfully. The tracking unit is only activated when you ring its number. A much neater solution is of course to use phones that can be controlled via serial ports. Been checking it last night...so much things can be done to it. The biggest problem is programming the PIC to take advantage all of whats possible with data enabled phones.