bassplayer142 said:
We don't know what the FBI device did besides track the car. It probably communicated wireless when available and had some type of encryption. I could easily see the price getting high quickly.
Obviously the most efficient solution would've been to use SMS messaging of GPS location at regular intervals, but that would make the device even cheaper! You can get a model just like that for 80 bucks on ebay. They can send commands to it via SMS to update the interval, etc. No encryption is necessary as the cellular messages are already encrypted. If the concern is being able to read the tracking data from device directly, its easily solved by not keeping cache stored, which really nobody would bother with anyway.
No. The bottom line is, this could've been made much smaller. Even added an external solar panel for trickle charging, this thing could still work for a few days. Or forget the transmitting and just use it as a logger, at 50mA gps logger this would run for 2 weeks on a 2Ah battery pack.
Matter of fact why don't we build one for them?
GPS+GPRS - Telit GM862 $160
http://www.sparkfun.com/commerce/product_info.php?products_id=7917
Arduino main board = $25
http://www.sparkfun.com/commerce/product_info.php?products_id=666
2Ah battery = $17
http://www.sparkfun.com/commerce/product_info.php?products_id=8483
The GPS/GPRS module draws on average 250 mA, Arduino main board is 50 mA, so your total draw is around 300 mA, which should last you for 6 hours, or 360 minutes, with average acquisition time of 30 seconds and parsing delay and SMS text message sending, I'd say you can set this to beacon mode for 1 minute poweron intervals. So you can send updates for 300+ times. If you space the intervals for once every 30 minutes that is 6 days, and if you go for once every hour, that's 12 days of operation. Stap 2 of these battery packs and it can last a month. Add accelerometer to reset the timer for only when the car moves and you can have even better battery time and tracking patterns
Total budget: $202 + shipping. And this is all for off the shelf parts from an overpriced store.
Better yet, add a few more battery packs, a detonator and a pack of C4 and strap this bad boy on the gas tank. Tracking + remote termination in one
