Transcript Compass, Gyro etc.

Compasses, Accelerometers, and
Gyros,
TYWu
Compass
• Principles
– The earth is a huge
magnet.
– Any freely suspended
magnet will align itself
with the earth’s magnetic
poles.
– The compass is a selfcontained unit requiring
no external power
source.
Compass
• Principles
– The strength of the earth's magnetic field is about
0.5 to 0.6 gauss and has a component parallel to
the earth's surface that always points toward the
magnetic north pole.
– In the northern hemisphere, this field points down. At
the equator, it points horizontally and in the southern
hemisphere, it points up.
– This angle between the earth’s magnetic field and the
horizontal plane is defined as an inclination angle.
Another angle between the earth's magnetic north and
geographic north is defined as a declination angle in
the range of ± 20º depending on the geographic location.
Compass
• Northerly Turning
(Dip) Error
– The earth’s magnetic
field causes the
compass to dip to
the low side of the
turn.
– In the Northern
Hemisphere: Lag
North, Lead South.
LAG NORTH
Compass
• Acceleration/De
celeration Error
– Most
pronounced on
headings of east
and west.
– Accelerate north,
Decelerate
south.
Compass
• 3-Axis Digital (Electronic)
Compass
• 3-Axis Digital Magnetometer
– LSM303DLH (MEMS)
• LSM303DLH has a magnetic field
full-scale of ±1.3 / ±1.9 / ±2.5 / ±4.0 /
±4.7 / ±5,6 / ±8.1 gauss
• Fully selectable by the user.
• High current in wiring and printed
circuit traces can be the cause of errors
in magnetic field measurements for
compassing.
Compass
• Compensated Compassing
Compass
• A Working Electronic Compass System
– Hardware design to make sure the MCU can get clean
raw data from the accelerometer and the magnetic
sensor
– Accelerometer calibration to obtain parameters to
convert accelerometer raw data to normalized values
for pitch and roll calculation
– Magnetic sensor calibration to obtain parameters to
convert magnetic sensor raw data to normalized values
for the heading calculation
Accelerometers
• Gyroscopes & Accelerometers Used in the
Airplane & Vehicle
Accelerometers
• 3-Axis Digital Accelerometer
– LSM303DLH (MEMS)
• A linear acceleration full-scale of ±2 g / ±4 g / ±8 g
• Fully selectable by the user.
Accelerometers
• 3-Axis Digital Accelerometer
– ADXL335
• Single-supply operation: 1.8 V to 3.6 V
• Measure acceleration with a minimum full-scale
range of ±3 g.
• Measure the static acceleration of gravity in tiltsensing applications, as well as dynamic
acceleration resulting from motion, shock, or
vibration.
Accelerometers
• ADXL335
– Application
•
•
•
•
•
Mobile devices
Gaming systems
Disk drive protection
Image stabilization
Sports and health devices
Accelerometers
• ADXL335
Accelerometers
• ADXL335
• Output Response vs. Orientation to Gravity
• However, the spec. and my experiment are
inconsistent!
Accelerometers
• Specification
Accelerometers
• MMA7361
Accelerometers
• MMA7361
Accelerometers
• MMA7361
Accelerometers
• MMA7361
Gyro
• 3 Axes of Angular
Freedom
– Spin Axis
– Horizontal Axis
– Vertical Axis
Gyro
• Applications
– Motion control with MMI (man-machine
interface)
– Appliances and robotics
– Gaming and virtual reality input devices
– Navigation
– Etc.
Gyro
• Roll, Pitch, and Yaw
Gyro
• 3-Axis Digital Gyroscope
(MEMS Motion Sensor)
– L3G4200D
Gyro
• Dual axis pitch and roll
±100°/s analog gyroscope
– LSM303DLH
Experiment I
• Arduino
• LSM303DLH 3D
Compass and
Accelerometer
Carrier with Voltage
Regulators
Experiment I
• LSM303DLH Arduino Library
– https://github.com/ryantm/LSM303DLH/tree/master/LS
M303DLH
• Wire Library
– This library allows you to communicate with
I2C / TWI devices. On most Arduino boards,
SDA (data line) is on analog input pin 4, and
SCL (clock line) is on analog input pin 5. On
the Arduino Mega, SDA is digital pin 20 and
SCL is 21
Experiment I
• SDA is defined
in ./libraries/SD/utility/Sd2PinMap.h
Experiment I
• The board for the LSM303DLH can be
purchased on Pololu
• Make the following connections with wires
between Arduino Uno/Duemilanove and
LSM303DLH board
–
–
–
–
5V -> VIN
GND -> GND
Analog Pin 5 -> SCL
Analog Pin 4 -> SDA
Experiment I
• Sketch
#include <Wire.h>
#include <LSM303DLH.h>
LSM303DLH compass;
void setup() {
Serial.begin(9600);
Wire.begin();
compass.enable();
}
Experiment I
void loop() {
compass.read();
Serial.print("Accel.: ");
Serial.print("X=");
Serial.print(compass.a.x);
Serial.print(", Y=");
Serial.print(compass.a.y);
Serial.print(", Z=");
Serial.println(compass.a.z);
Serial.print("Compass: ");
Serial.print("X=");
Serial.print(compass.m.x);
Serial.print(", Y=");
Serial.print(compass.m.y);
Serial.print(", Z=");
Serial.println(compass.m.z);
delay(1000);
}
Experiment I
• Results
Experiment I
• Results
Experiment II
• L3G4200D 3-Axis
Gyro Carrier with
Voltage Regulator
Experiment II
• LPR510AL DualAxis (Pitch and Roll
or XY) Gyro with
±100°/s and ±400°/s
Ranges
Experiment II
• LPR510AL IC
– Output Response vs. Rotation
Experiment II
• Mechanical characteristics
Experiment II
• LPR510AL
– The axes of rotation are pitch (x) and roll (y) for
LPR510AL
Experiment II
• These two-axis gyros are essentially carrier
boards or breakout boards for ST’s
LPR510AL, LPY510AL, LPR550AL, and
LPY550AL MEMS (micro-electro-mechanical
systems) gyroscopes.
Experiment II
• LPR510AL
– For 5V microcontroller applications, the power
down (PD) and self test (ST) lines should not be
driven high. It is always safe for you to drive these
lines low.
Experiment II
• LPR510AL
– The self-test input is pulled low by default.
To activate the self-test feature, drive the
line to Vdd (the same pull-up trick as above
can be used for 5V applications).
Experiment II
• LPR510AL
– The devices can be powered directly through the
Vdd/3.3V pin using a supply that is within the gyro
chips’ acceptable power supply range of 2.7 V to
3.6 V.
Experiment II
• LPR510AL
– Alternatively, the boards can be powered by higher
voltages, up to 16 V, using the VIN pin, which
connects to a low-dropout 3.3V regulator. In this
configuration, the 3.3V pin can serve as an output
to be used as a reference voltage or power source
for other low-power devices (up to around 50 mA,
depending on the input voltage).
Experiment II
• LPR510AL
– Please note that unlike some other gyros and
accelerometers, the outputs are not ratiometric
with the Vdd/3.3V power line (i.e. at zero rate of
rotation, the output should equal Vref, not half of
the Vdd/3.3V supply).
Experiment II
• Connection
LPR510AL
Arduino UNO
VIN
3.3V
GND
GND
Y
A1
X
A0
PD
GND
Experiment II
• Result
– Steady State Position
258/1023*5V = 1.26V
(But, the value described
in data sheet is 1.23V)
Experiment III
AREF
• ADXL335 & Arduino
• (ZY?)
A0
A1
A2
Experiment III
• Sketch
#define parameter 0.009765625
// AXDL335 用，代表 10 位元的 ADC 轉換 1 個刻度所代表的 G 值。
(3.3/1024/0.33)
#define rad 57.295779513082
// 徑度。(360/2*PI)
double X,Y,Z,Xangle,Yangle,Zangle;
int Xread,Yread,Zread;
int Xref = 505;
int Yref = 496;
int Zref = 496;
// XYZ 軸的偏差矯正參數，可透過此參數調整 XYZ 軸 0G 時的標準值
int Xinput = 0;
// X 軸的類比電壓輸入腳位
int Yinput = 1;
// Y 軸的類比電壓輸入腳位
int Zinput = 2;
// Z 軸的類比電壓輸入腳位
Experiment III
void setup() {
Serial.begin(9600);
// 串列傳輸的鮑率設定
analogReference(EXTERNAL);
// 設定外部參考電壓
}
void loop() {
Xread = analogRead(Xinput);
// 將 X 軸的輸入電壓存到所設定的變數
Yread = analogRead(Yinput);
// 將 Y 軸的輸入電壓存到所設定的變數
Zread = analogRead(Zinput);
// 將 Z 軸的輸入電壓存到所設定的變數
X = (Xread-Xref)*parameter;
// 計算 X 軸的 G 值
Y = (Yread-Yref)*parameter;
// 計算 Y 軸的 G 值
Z = (Zread-Zref)*parameter;
// 計算 Z 軸的 G 值
Xangle = asin(constrain(X, -1, 1) )*rad; // 計算出 X 軸的傾斜角度
Yangle = asin(constrain(Y, -1, 1) )*rad;
// 計算出 Y 軸的傾斜角度
Zangle = asin(constrain(Z, -1, 1) )*rad;
// 計算出 Y 軸的傾斜角度
Experiment III
Serial.print(" X = "); printDouble(X,2); Serial.print(" G");
Serial.print(9,BYTE);
Serial.print(" Y = "); printDouble(Y,2); Serial.print(" G");
Serial.print(9,BYTE);
Serial.print(" Z = "); printDouble(Z,2); Serial.print(" G");
Serial.print(9,BYTE);
Serial.print(9,BYTE);
Serial.print("thidaX = "); printDouble(Xangle,1); Serial.print(9,BYTE);
Serial.print(" thidaY = "); printDouble(Yangle,1); Serial.print(9,BYTE);
Serial.print(" thidaZ = "); printDouble(Zangle,1); Serial.println(" ");
delay(500);
}
Experiment III
void printDouble( double val, byte precision){
if(val < 0.0){
Serial.print('-');
val = -val;
}
Serial.print (int(val)); //prints the int part
if( precision > 0) {
Serial.print("."); // print the decimal point
unsigned long frac;
unsigned long mult = 1;
byte padding = precision -1;
while(precision--)
mult *=10;
Experiment III
if(val >= 0)
frac = (val - int(val)) * mult;
else
frac = (int(val)- val ) * mult;
unsigned long frac1 = frac;
while( frac1 /= 10 )
padding--;
while( padding--)
Serial.print("0");
Serial.print(frac,DEC) ;
}
}
Experiment III
• Result
Experiment III
• Another Sketch (Very Simple)
const int xpin = A0;
// x-axis of the accelerometer
const int ypin = A1;
// y-axis
const int zpin = A2;
// z-axis (only on 3-axis models)
int sampleDelay = 500; //number of milliseconds between readings
void setup()
{
Serial.begin(9600);
pinMode(xpin, INPUT);
pinMode(ypin, INPUT);
pinMode(zpin, INPUT);
}
Experiment III
void loop()
{
int x = analogRead(xpin);
int y = analogRead(ypin);
int z = analogRead(zpin);
float zero_G = 512.0;
float scale = 102.3;
Serial.print(((float)x - zero_G)/scale);
Serial.print("\t");
Serial.print(((float)y - zero_G)/scale);
Serial.print("\t");
Serial.print(((float)z - zero_G)/scale);
Serial.print("\n");
delay(sampleDelay);
}
Experiment IV
• MMA7361
Analog2
Analog1
Analog3
3.3V
AREF
3.3V
GND
3.3V
3.3V
Experiment IV
• Sketch
• http://120.107.171.121/~tywua/sub/ISAR/M
Y_MMA7361.pde
Experiment IV
• Result
Demo
• Prototype of Mimic Robotic Arm in Arduino
and Gyroscope
– http://www.youtube.com/watch?v=ai2RiGMyV08
Reference
• References
– http://www.instructables.com/id/AccelerometerGyro-Tutorial/
– http://www.instructables.com/id/AccelerometerGyro-Tutorial/step2/Gyroscope/
– http://www.arduino.cc/playground/Main/Gyro