Table of contents
3.Introduction
4.Specification requirements
5.Solutions suggestions
6.The magnetic fields sensors
7.The inclination measurement system
8.The gyroscope
9.The data acquisition system
10.Communication system
11.The power supply
12.Realisation of the PCB
13.The embedded system
14.Static Library Util.a
15.ViewPort
16.Xcompass
17.Sensors controller commands
18.Test
19.Future improvements
20.Conclusion
21.References

5.    Solutions suggestions

To realise our compass, we have typically two possible approaches:

• To buy and extend a commercial compass according to our requirements.
• To build the entire system according to the specification.

Let’s have a look on the cheapest solution on the market.

5.1.                     The CMPS03: Robot compass module

This compass module has been specifically designed to assist robots’ navigation. Therefore, it produces a unique number that represents the direction the robot is facing. The compass uses the Philips KMZ51 magnetic field sensor to detect the Earth magnetic field. The output from two of them is used to compute the direction of the horizontal component of the Earth magnetic field. This device requires 5V-power supply and uses an I2C interface to communicate with the other system. This last specification will require many modifications to use it with a RS485 connection.

Figure 2: The CMPS03 magneto module

5.2.                     The Vector 2X

This device can be use as compass or magneto sensors. The module will apply correction for hard iron distortion to compensate for magnetic interference in harsh environments but it does not provide tilt compensation. The maximum resolution of the angle is 1° that could be sufficient for our application. As the previous system, it requires 5V-power supply, but it uses an SPI interface to communicate.

Consequently, we will have the same modification to do for using the Vector 2X with the MMR or the SMR.

5.3.                     The HMC2003

Figure 4: The HMC2003

It appears that to buy a commercial system is not the best solution for the assignment. In addition the price varies from product to product. The two first suggestions are not very expensive (about 22£ for the CMPS03 and 50$ for the Vector 2X); but we would have to add the cost of the modifications. Nevertheless, these different compasses give a good base to design our own system based on the above considerations.

Another solution to realise our navigation system could be to use several gyros on each axis. In this way, the drift, which is the major problem with the gyro, could be compensated. Many application based on this sensor have already been developed in IAU. The adjustments of an existing model are not very easy, and could require lots of work to adapt it to our specification.