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LOOKING THROUGH THE INTERNET

A Prototype Security System
by Skylar Lei, Jim Haslett, and Mike Smith

Start • Web Server Choice • Interactive GUI • Video System • Remote Camera System • Control RF Link • Solar Power Module • • Sources

REMOTE CAMERA SYSTEM

The equipment at the remote camera sites communicates with the base station using RF links. The remote equipment is powered by solar batteries to avoid long wiring.

The camera and the video transmitter are activated on request to save the power collected by a solar panel. As a result, only one camera system will be sending signals to the base station at a time. This implies that the video transmitter/receiver pairs can use the same carrier frequency without worrying about interference.

To keep the cost of our prototype video RF link at our remote site to a minimum, we chose commercial transmitters and receivers that operate in the 2.4-GHz band. This band is less crowded, offering less interference than the 900-MHz band, which is currently occupied by cellular and cordless phones and various remote-controlled equipment (e.g., garage door openers). It’s also easier to find commercial transmitter/receiver pairs in the 2.4-GHz band.

A hoped-for side advantage is that the system will be unaffected if the USS Carl Vinson ever sails up a local stream near our camera. Apparently, when this aircraft carrier sailed into Hobart Harbour (Tasmania, Australia), its navigation radar overpowered all the remote garage-door openers in town! (New Scientist, 24 April 1999, www.newscientist.com)

The cost of the video RF transmitter/receiver pair depends on the transmission range. For the prototype, we used the Wavecom Jr. model 15-1970 which allows for 100 m, line of sight. The model GW-2400 from Polaris Industries ($220 a pop) will meet our customer’s final requirements for transmissions of up to 300 m.

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