Low-power direction indication system based on magnetoresistive sensor

The compass is an important navigation tool and has application value in many occasions. In order to make the performance of the compass even better and the application area more extensive, we designed and manufactured a low-power direction indication system based on a magnetoresistive sensor. In some special terrain conditions, GPS will not work well, and this direction indication system will not be affected, especially for some occasions that only require detection direction without needing to detect the latitude and longitude.

1 Features and Indicators Requirements 1.1 The overall function and features of the direction of the indication system is mainly a direction indicating function, graphic display, magnetic declination correction and information locking function, and has a portable and low-power features. The interface setup diagram is shown in Figure 1.

The direction indication system has a wide range of applications and can be applied to the following areas: hand-held direction indication systems, on-board navigation and travel control, compasses in mobile phones, telescope positioning, direction indications in medical devices, and land and sea navigation systems.

Interface Settings Figure 1.2 Requirements and Indicators for Design:

To achieve the above functions, the system must meet the following requirements:

(1) All the components in the system have the characteristics of small size and low power consumption.

(2) All components in the system are standard low-cost components; especially microcontrollers, and there should be as many on-chip external modules as possible (such as A/D and D/A converters).

(3) Because the output signal of the sensor is very small, each component is required to have strong anti-noise capability, and the power supply output has a small ripple.

(4) The following information can be displayed:

- display the heading in numbers and figures; - display the heading in the nearest azimuth text.

(5) The reading of the compass is referenced to geographically north-north-north according to the HMC105X data sheet. When connecting a low-noise amplifier and a 12- to 162-bit analog-to-digital converter (A/D), the HMC105X series can be used. Perform extremely accurate measurements. The measurement error is less than 1° and the power consumption of the circuit is less than 115 mW.

2 system design:

2.1 Overall System Design Figure 2 shows the block diagram of the direction indication system. This is its minimum setting. The sensor unit is a part that collects the earth's magnetic field and converts the earth's magnetic field signal into an electric signal. The signal adjustment unit amplifies and filters weak earth magnetic signals and converts the analog signals into digital signals. The data processing unit outputs the adjustment unit. The digital data is analyzed to determine the desired direction and the true North direction angle, and the local magnetic declination is corrected. The liquid crystal display unit displays the orientation angles in both graphical and digital forms.

In this system, the sensor unit consists of a two-axis magnetoresistive sensor HMC1052. The signal conditioning unit is a small-signal amplifying circuit composed of an instrumentation amplifier. MSP430 microcontroller as the core of data processing and signal control, data processing and direction determination unit.

The final display unit uses a 128 × 64 graphics dot matrix LCD.