Solutions suggestions

Table of contents
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
17.Sensors controller commands
19.Future improvements

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

CMPS03This 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

Figure 3: 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

The Honeywell HMC2003 is a high sensitivity, three axis magnetic sensor hybrid assembly used to measure low magnetic field strengths. Honeywell’s most

sensitive magneto-resistive sensors (HMC1001 and

HMC1002) are utilized to provide the reliability and precision of this magnetometer design. The HMC2003

interface is all analogue with critical nodes brought out to the pin interfaces for maximum user flexibility.

Although the characteristics of this device are very interesting, the price for this kind of device is so expensive (200$). In addition, the cost of each magneto sensors used to realise this system is inferior to 20$.

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.

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