Built-in 12bit AD converter chip, 16-bit data output
Immersion Gold PCB, Machine welding cess
Use chip: LSM303DLH
Power supply: 3-5v?Internal low dropout regulator?
Communication: standard IIC communication tocol
Magnetic field range:
1.3 / 1.9 / 2.5 /4.0 /4.7 /
5.6 / 8.1 gauss
Acceleration Range: 2 g / 4 g / 8 g
It offers 51 single test code
vide STM32 test code
LSM303D related presentations:
LSM303DLH chip accelerometer, magnetometer, A / D converters and signal conditioning integrated circuit, still through the I2C bus and cessor communication. Thus only a single chip to achieve a 6-axis detection data and output, reduce the customer's design effort and reduce PCB board footprint, reducing the device cost.
LSM303DLH peripheral devices require very little connection is also very simple, magnetometer and accelerometer each have a I2C bus and cessor communication. If the customer's I / O interface level is 1.8V, Vdd_dig_M, Vdd_IO_A and Vdd_I2C_Bus can pick 1.8V power supply, Vdd above 2.5V power supply to use; if the client interface level is 2.6V, 1.8V requirements except Vdd_dig_M outside, the other can be used are 2.6V. In the above mentioned, LSM303DLH need to set / reset circuit in order to maintain the main magnetic field of AMR. C1 and C2 are set / reset circuit external matching capacitors, due to the set and reset pulse have certain requirements, the user should not arbitrarily change the size of C1 and C2.
To implement an electronic compass function, a three-axis magnetic field sensor and a triaxial acceleration sensor. With micro-mechanical cesses mature, STMicroelectronics will triaxial magnetometer and triaxial accelerometer integrated in one package combo sensor module LSM303DLH, user-friendly design in a short time a low cost, high performance electronics compass. Taking LSM303DLH example to discuss implementation of the device works, technical parameters and electronic compass.
1. ST integrated magnetometer and accelerometer sensor module LSM303DLH
1.1 magnetometer works
In LSM303DLH the magnetometer anisotropic magnetoresistive?Anisotropic Magneto-Resistance?Material to detect the size of the space magnetic induction. This alloy has a crystal structure of the external magnetic field is very sensitive to changes in the strength of the magnetic field will cause the value of AMR's own resistance to change.
In the manufacturing cess, so that a strong magnetic field is applied in one direction of magnetization in the AMR establish a main magnetic field, the magnetic field perpendicular to the main axis is called the sensitive axis of the AMR, as shown in FIG. In order to measure the change results in a linear manner, metal wire material on the AMR 45? Angle of inclination are arranged, from which the current flows through the wire. The main magnetic field and current direction of the magnetic field from the initial set up on AMR material 45? Angle.
When there is an external magnetic field Ha, the AMR main magnetic field direction will change rather than the initial direction, then the angle between the magnetic field and current direction will change as shown in FIG. For AMR materials, changes in the angle will cause changes in AMR's own resistance, and a linear relationship,
ST use Wheatstone bridge AMR detecting a change in resistance. R1 / R2 / R3 / R4 is the same as the initial state of AMR resistance, but R1 / R2 and R3 / R4 have opposite magnetization characteristics. When the external magnetic field is detected, R1 / R2 resistance value increase? R and R3 / R4 reducing R. Thus in the absence of external magnetic field, the output of the bridge is zero; when the external magnetic field in the output of the bridge is a small voltage V?.
1.2 Set / Reset (Set / Reset) circuit
Due to the impact of the external environment, the main magnetic field direction LSM303DLH in AMR is not permanent remain unchanged. LSM303DLH built-in set / reset circuit, through the internal metal coil generates periodic current pulses to restore the main magnetic field, as shown in FIG. It should be noted that the effect of the set pulse and the reset pulse is the same, just different directions only.
Set / reset circuit to LSM303DLH bring many advantages:
1? Even if the interference of external magnetic field encountered after interference disappears LSM303DLH can resume normal operation again without the need for user calibration.
2? Long working hours can be maintained even if the initial magnetization direction to achieve accurate measurements, temperature variations will not chip or internal noise increases affect measurement accuracy.
3? Eliminate the drift caused by the deviation of the bridge.
1.3 LSM303DLH performance parameters
LSM303DLH integrated triaxial magnetometer and triaxial accelerometer, a digital interface. Magnetometer measurement range from 1.3 Gauss to 8.1 Gauss is divided into seven files, the user can ly choose. And in less than 20 Gauss magnetic field are able to maintain a consistent measurement results and the same sensitivity. Its resolution can reach 8 mGauss and internal 12-bit ADC, accurate measurement of the magnetic field strength. And Hall-effect principle of the magnetometer compared LSM303DLH low power consumption, high accuracy, good linearity, and does not require temperature compensation.
LSM303DLH with automatic detection. When the position control registers A, chip self-test circuit will duce a magnetic field to about the size of the excitation signal and output. Users can output data to determine whether the chip is working perly.
As a highly integrated sensor module, in addition to the magnetometer LSM303DLH also incorporates a high-performance accelerometers. Accelerometer also uses 12 ADC, can achieve the measurement accuracy of 1mg. Accelerometer can operate in low-power mode and sleep / wake-up function, can greatly reduce power consumption. Meanwhile, an accelerometer is also integrated 6-axis direction detection, two grammable interrupt interface.
For portable devices, the device power consumption is very ant and directly affect its standby time. LSM303DLH can magnetometer and accelerometer control the power mode, put it into sleep or low-power mode. And the user can adjust the magnetometer and accelerometer data update frequency, to adjust the power level. In the magnetometer data update frequency is 7.5Hz, accelerometer data update frequency is 50Hz, the current consumption is typically 0.83mA. In standby mode, the current consumption is less than 3uA.
2. iron magnetic interference and calibration
Electronic compass direction mainly by sensing the presence of the Earth's magnetic field to calculate the magnetic North Pole. However, due to the Earth's magnetic field in general only a weak 0.5 gauss, and a regular speaker phone apart when there will be about 4 gauss 2 cm, the motor will have a cell phone about 6 gauss at a distance of 2 cm, this feature allows for the electronic measuring device surface of the earth magnetic field is very susceptible to interference from electronic equipment itself.
Magnetic interference is due to having a magnetic substance or substances can affect the existence of the local magnetic field strength, so that the magnetic sensor is placed on the Earth's magnetic field position deviation occurs. 11, in the XYZ coordinate system of the magnetic sensor, the green circle represents the Earth's magnetic field vector around the z-axis rotation of the circumference of the track jection in the XY plane, no longer under any external magnetic interference, this track will It will be a standard in O (0,0) as the center of the circle. When the presence of external magnetic interference, the measured magnetic field strength of the Earth's magnetic field vector and the point for magnetic interference and vector. Referred to as:
Generally believed that magnetic interference at this point can be regarded as a constant vector. There are many factors that can cause magnetic interference, such as motors and speakers placed in the circuit board, as well as materials containing iron and other metals such as nickel and cobalt shield, screws, resistors, LCD backplane and housing and so on. Also according to Ampere's law will have a current through the wire generates a magnetic field, as shown in Figure 12.
To calibrate the magnetic interference from the circuit board, the main job is to be determined by calculation.
2.1 plane calibration method
For calibration XY axis magnetic sensor device will be equipped with a rotation in the XY plane, it is equivalent to the Earth's magnetic field vector around through the point O (x, y) perpendicular to the normal rotation in the XY plane, and the red circle is during the rotation the magnetic field vector in the XY plane jection trajectory. This can be found in the center position ((Xmax + Xmin) / 2, (Ymax + Ymin) / 2). Also the equipment in the XZ plane rotation can be Earth's magnetic field trajectory on the XZ plane of the circle, which can be obtained three-dimensional space vector magnetic interference (x, y, z).
2.2 stereo, 8 calibration method
Under normal circumstances, when the rotation of the device with a sensor in the air in all directions, the measured value consisting of the geometry of space is actually a ball, all the sample points fall on the ball's surface, 13, this is within the same two-dimensional jection plane obtained similar round.
In this case, by obtaining a sufficient sample points the center O (x, y, z), i.e., the size and direction of the fixed magnetic field vector. Formula is as follows:
8 characters calibration method requires the user to use the device needs to be calibrated in the air, do 8 characters shaking, as much as possible so that the normal direction pointing device space all eight quadrants in principle.
2.2 decahedron calibration method
Similarly, the surface 10 by the calibration method, can also achieve the purpose of calibration.
3. Tilt angle calculation and navigation
After calibrating electronic compass in a horizontal plane has been normal use. But more often than not maintain the level of mobile phone, and it usually has a horizontal angle. This angle can affect the accuracy of the heading angle, tilt compensation is required by the acceleration sensor.
For an object in the air attitude, the navigation system has long been defined, as shown in Figure 17, Android also adopted this definition. The Pitch () is defined as the angle between the horizontal plane and the x-axis, illustrating direction is positive; Roll () is defined as the angle between the horizontal plane and the y-axis direction shown as a positive direction. Pitch angle error caused by the heading angle shown in Figure 18. As can be seen in the x-axis direction of the tilt angle of 10 degrees can cause the heading angle of the maximum error of 7-8 degrees.
Phone inclined posture in the air by three-axis acceleration sensor detects the three-axis gravity acceleration components, and then can be calculated by Equation 2 Pitch and Roll.
In the current popular android phones, many of which are equipped with compass function. To achieve this, only equipped with a combo sensor module vided LSM303DLH ST.
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