Lesson 14 ADXL345¶
Introduction¶
In this lesson, we will learn how to use the acceleration sensor ADXL345.
Principle¶
ADXL345
The ADXL345 is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16 g. Digital output data is formatted as 16-bit two’s complement and is accessible through either an SPI (3- or 4-wire) or I2C digital interface.
The ADXL345 is well suited to measure the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables the inclination change measurement by less than 1.0°. And the excellent sensitivity (3.9mg/LSB @2g) provides a high-precision output of up to ±16g. In this experiment, I2C digital interface is used.
Experimental Procedures¶
Step 1: Build the circuit.
The I2C interface is used in the following program. Before running the program, please make sure the I2C driver module of Raspberry Pi has loaded normally(Refer to Appendix).
For C Language Users:¶
Step 2: Change directory.
cd /home/pi/Sunfounder_SuperKit_C_code_for_RaspberryPi/14_ADXL345/
Step 3: Compile.
gcc adxl345.c -o adxl345 -lwiringPi
Step 4: Run.
sudo ./adxl345
Note
If it does not work after running, or there is an error prompt: “wiringPi.h: No such file or directory”, please refer to C code is not working?.
Code
#include <wiringPiI2C.h>
#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#define DevAddr 0x53 //device address
struct acc_dat{
int x;
int y;
int z;
};
void adxl345_init(int fd)
{
wiringPiI2CWriteReg8(fd, 0x31, 0x0b);
wiringPiI2CWriteReg8(fd, 0x2d, 0x08);
// wiringPiI2CWriteReg8(fd, 0x2e, 0x00);
wiringPiI2CWriteReg8(fd, 0x1e, 0x00);
wiringPiI2CWriteReg8(fd, 0x1f, 0x00);
wiringPiI2CWriteReg8(fd, 0x20, 0x00);
wiringPiI2CWriteReg8(fd, 0x21, 0x00);
wiringPiI2CWriteReg8(fd, 0x22, 0x00);
wiringPiI2CWriteReg8(fd, 0x23, 0x00);
wiringPiI2CWriteReg8(fd, 0x24, 0x01);
wiringPiI2CWriteReg8(fd, 0x25, 0x0f);
wiringPiI2CWriteReg8(fd, 0x26, 0x2b);
wiringPiI2CWriteReg8(fd, 0x27, 0x00);
wiringPiI2CWriteReg8(fd, 0x28, 0x09);
wiringPiI2CWriteReg8(fd, 0x29, 0xff);
wiringPiI2CWriteReg8(fd, 0x2a, 0x80);
wiringPiI2CWriteReg8(fd, 0x2c, 0x0a);
wiringPiI2CWriteReg8(fd, 0x2f, 0x00);
wiringPiI2CWriteReg8(fd, 0x38, 0x9f);
}
struct acc_dat adxl345_read_xyz(int fd)
{
char x0, y0, z0, x1, y1, z1;
struct acc_dat acc_xyz;
x0 = 0xff - wiringPiI2CReadReg8(fd, 0x32);
x1 = 0xff - wiringPiI2CReadReg8(fd, 0x33);
y0 = 0xff - wiringPiI2CReadReg8(fd, 0x34);
y1 = 0xff - wiringPiI2CReadReg8(fd, 0x35);
z0 = 0xff - wiringPiI2CReadReg8(fd, 0x36);
z1 = 0xff - wiringPiI2CReadReg8(fd, 0x37);
printf(" x0 = %d ",x0);printf("x1 = %d \n",x1);
printf(" y0 = %d ",y0);printf("y1 = %d \n",y1);
printf(" z0 = %d ",z0);printf("z1 = %d \n",z1);
acc_xyz.x = (int)(x1 << 8) + (int)x0;
acc_xyz.y = (int)(y1 << 8) + (int)y0;
acc_xyz.z = (int)(z1 << 8) + (int)z0;
if(acc_xyz.x > 32767){
acc_xyz.x -= 65536;
}
if(acc_xyz.y > 32767){
acc_xyz.y -= 65536;
}
if(acc_xyz.z > 32767){
acc_xyz.z -= 65536;
}
return acc_xyz;
}
int main(void)
{
int fd;
struct acc_dat acc_xyz;
fd = wiringPiI2CSetup(DevAddr);
if(-1 == fd){
perror("I2C device setup error");
}
adxl345_init(fd);
while(1){
acc_xyz = adxl345_read_xyz(fd);
printf("x: %d y: %d z: %d\n", acc_xyz.x, acc_xyz.y, acc_xyz.z);
delay(1000);
}
return 0;
}
For Python Users:¶
Step 2: Change directory.
cd /home/pi/Sunfounder_SuperKit_Python_code_for_RaspberryPi
Step 3: Run.
sudo python3 14_ADXL345.py
Now, rotate the acceleration sensor, and you should see the values printed on the screen change.
Code
from I2C import I2C
from time import sleep
import RPi.GPIO as GPIO
from sys import version_info
if version_info.major == 3:
raw_input = input
class ADXL345(I2C):
ADXL345_ADDRESS = 0x53
ADXL345_REG_DEVID = 0x00 # Device ID
ADXL345_REG_DATAX0 = 0x32 # X-axis data 0 (6 bytes for X/Y/Z)
ADXL345_REG_POWER_CTL = 0x2D # Power-saving features control
ADXL345_DATARATE_0_10_HZ = 0x00
ADXL345_DATARATE_0_20_HZ = 0x01
ADXL345_DATARATE_0_39_HZ = 0x02
ADXL345_DATARATE_0_78_HZ = 0x03
ADXL345_DATARATE_1_56_HZ = 0x04
ADXL345_DATARATE_3_13_HZ = 0x05
ADXL345_DATARATE_6_25HZ = 0x06
ADXL345_DATARATE_12_5_HZ = 0x07
ADXL345_DATARATE_25_HZ = 0x08
ADXL345_DATARATE_50_HZ = 0x09
ADXL345_DATARATE_100_HZ = 0x0A # (default)
ADXL345_DATARATE_200_HZ = 0x0B
ADXL345_DATARATE_400_HZ = 0x0C
ADXL345_DATARATE_800_HZ = 0x0D
ADXL345_DATARATE_1600_HZ = 0x0E
ADXL345_DATARATE_3200_HZ = 0x0F
ADXL345_RANGE_2_G = 0x00 # +/- 2g (default)
ADXL345_RANGE_4_G = 0x01 # +/- 4g
ADXL345_RANGE_8_G = 0x02 # +/- 8g
ADXL345_RANGE_16_G = 0x03 # +/- 16g
def __init__(self, busnum=1, debug=False):
self.accel = I2C(self.ADXL345_ADDRESS, busnum, debug)
if self.accel.readU8(self.ADXL345_REG_DEVID) == 0xE5:
# Enable the accelerometer
self.accel.write8(self.ADXL345_REG_POWER_CTL, 0x08)
def setRange(self, range):
# Read the data format register to preserve bits. Update the data
# rate, make sure that the FULL-RES bit is enabled for range scaling
format = ((self.accel.readU8(self.ADXL345_REG_DATA_FORMAT) & ~0x0F) |
range | 0x08)
# Write the register back to the IC
seld.accel.write8(self.ADXL345_REG_DATA_FORMAT, format)
def getRange(self):
return self.accel.readU8(self.ADXL345_REG_DATA_FORMAT) & 0x03
def setDataRate(self, dataRate):
# Note: The LOW_POWER bits are currently ignored,
# we always keep the device in 'normal' mode
self.accel.write8(self.ADXL345_REG_BW_RATE, dataRate & 0x0F)
def getDataRate(self):
return self.accel.readU8(self.ADXL345_REG_BW_RATE) & 0x0F
# Read the accelerometer
def read(self):
raw = self.accel.readList(self.ADXL345_REG_DATAX0, 6)
print (raw)
res = []
for i in range(0, 6, 2):
g = raw[i] | (raw[i+1] << 8)
g = 65535 - g
if g > 32767:
g -= 65535
res.append(g)
return res
# Simple example prints accelerometer data once per second:
def main():
accel = ADXL345()
accel.setRange(accel.ADXL345_RANGE_16_G)
while True:
x, y, z = accel.read()
print('X: %.2f, Y: %.2f, Z: %.2f'%(x, y, z))
sleep(1) # Output is fun to watch if this is commented out
def destroy():
exit()
def destroy():
exit()
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
destroy()
