Development of Mobile Robot Based on I
2
C Bus System
205
The PC station and RF radio module are selected to produce signal and work as master device.
The system of mobile robot can directly connect to I
2
C devices and other devices, which cannot
support I
2
C system, they can be connected through microcontroller with interface circuit.
5.2.1 The I
2
C bus devices
Standard I
2
C devices operate up to 100Kbps, while fast-mode devices operate at up to
400Kbps. A 1998 revision of the I
2
C specification (v. 2.0) added a high-speed mode running
at up to 3.4Mbps. Most of the I
2
C devices available today support 400Kbps operation.
Higher-speed operation may allow I
2
C to keep up with the rising demand for bandwidth in
multimedia and other applications.
5.2.1.1 Compass sensor
The first I
2
C slave device is compass sensor module as shown in Fig. 22. This sensor can
work on the I
2
C bus without addition circuit. This compass module has been specifically
designed for use in robots as an aid to navigation. The aim was to produce a unique number
to represent the direction the robot is facing. The compass uses the Philips KMZ51 magnetic
field sensor, which is sensitive enough to detect the earth’s magnetic field. The output from
two of them mounted at right angles to each other is used to compute the direction of the
horizontal component of the earth’s magnetic field. The compass module requires a 5v
power supply at a nominal 15mA. The pulse width varies from 1mS (0°) to 36.99mS (359.9°)
– in other words 100uS/° with a +1mS offset. On I
2
C bus, there is an important
consideration that consists of the address from manufacturer and the address from user.
Fig. 22. Compass module slave device
5.2.1.2 Gyroscope sensor
A gyroscope is a device for measuring or maintaining orientation, based on the principles of
angular momentum (Komoriya, K. and Oyama, E., 1994). A mechanical gyroscope is
essentially a spinning wheel or disk whose axle is free to take any orientation. This orientation
changes much less in response to a given external torque than it would without the large
angular momentum associated with the gyroscope's high rate of spin. Since external torque is
minimized by mounting the device in gimbals, its orientation remains nearly fixed, regardless
of any motion of the platform on which it is mounted.
Because this gyroscope is not designed
for the I
2
C bus system, it must be connected through microcontroller and read its
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