For the full article please see the Fall 2007 issue of Robot Magazine.
Using a Internet connection and a night vision infrared camera the WatchBot provides a robust remote mobile surveillance platform. Built on the iRobot Create, the WatchBot can be driven directly or use a fixed set of IR beacons to navigate around the house. By using beacons the remote operator does not have manually steer the robot. Instead the operator is free to pan and tilt the camera while the robot takes care of the nasty details of steering and obstruction avoidance.
The WatchBot uses an infrared beacon system for navigation. Using a scanning IR detector the robot can lock on and navigate toward a beacon. Once at the beacon the robot turns and navigates to the next beacon. By using multiple beacons any path can be marked out. The WatchBot can then traverse this path over and over again very much like a night watchman would make his or her nightly rounds.
The brain of the WatchBot is the new Propeller Chip from Parallax. The Propeller is actually eight individual microcontrollers called Cogs built into one chip. Each Cog has its own memory in addition to the main 32K of RAM which is shared by all eight. The Cogs can perform simultaneous tasks cooperatively or individually while sharing resources through a common hub. The Propeller has 32 I/O pins of which four are generally pre-allocated to an external EEPROM and the serial programming lines.
The WatchBot uses a wireless color video camera from Smarthome (#76004). This camera can transmit a standard video composite signal directly to a television or VCR up to 300 feet. By using a built-in IR illuminator it can see up to 45 feet in total darkness. A four channel 2.4 GHz receiver is included with the camera allowing you to expand the system with three other cameras. For this application the receiver is connected to an AVerDVD EZMaker video capture card mounted in a desktop PC.
Bluetooth technology is used for wireless communication to the robot. The WatchBot connects to a local PC using the Parallax Embedded Blue module (eb500). For the PC, Bluetooth support is provided by a D-Link Bluetooth USB adapter (DBT-120). By using these two modules a simple serial connection can be established from the WatchBot to the PC. This connection can be treated as a hardwired cable. All the error correction and security over this wireless “cable” is handled invisibly by the Bluetooth protocol.
Most of the WatchBot related components are mounted in or on a 10 x 8 Instrument Case available from Jameco Electronics (#18877). The camera mounting and IR sensor are located on the top of the case and all the electronic component are placed inside. The case is mounted to the Create using the four hard points located around the cargo bay. The voltage regulators used to reduce the Create’s 14.4 volt battery to a more manageable 12 and 9 volts are installed in the cargo bay.
The Parallax Propeller Proto Board was used to simplify the use of the Propeller Chip. It contains all the support hardware needed for the Propeller. This includes power supply, EEPROM, 5 MHz crystal, and programming connector. All the Propeller I/O pins are easily accessible using this board. All the wiring was done with wire-wrap. Direct point to point solder wiring could also have been used.
A detailed schematic and all the source code can be downloaded from the links on the right or from http://www.botmag.com/issue8. |
Robots with a Mission
