Course Name: Embedded System Design with ARM
Faculty Name: Dr. Kamalika Datta
Department : Computer Science and Engineering
Topic
Lecture 38: Accelerometer
Accelerometer: principle of operation
ADXL 335 accelerometer
Sensor: Accelerometer (Motion)
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What is an accelerometer?
• A dynamic sensor that can measure acceleration in one, two, or three orthogonal axes.
• Typically used in one of three modes:
• As an inertial measurement of velocity and position.
• As a sensor of inclination, tilt or orientation in 2/3 dimensions.
• As a vibration or impact (shock) sensor.
• Most accelerometers are based on Micro Electro-Mechanical Sensors (MEMS).
• Based on the displacement of a small mass etched into the silicon surface of the IC, and suspended
by small beams.
• As an acceleration is applied, a force develops (P = mf) that displaces the mass.
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• The displacement of the mass can be measured using capacitive sensing or
piezoelectric effect sensing.
• Change in capacitance, or generation of a voltage.
• The basic structure of an accelerometer consists of fixed plates and moving
plates (called mass).
• Acceleration deflects the moving mass and unbalances the differential capacitor
that results in a sensor output voltage amplitude which is proportional to the
acceleration.
• By measuring the acceleration along the x, y and z directions, it is possible to
calculate the inclination or tilt.
• It is also possible to calculate the angles of rotation along x, y and z axes (called roll,
pitch and yaw respectively).
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The ADSL 335 Accelerometer
• The ADXL 335 is a small, thin, low-power 3-axis
accelerometer with signal conditioned voltage outputs.
• It can measure the static acceleration due to gravity in tilt-
sensing applications, as well as dynamic acceleration
resulting from motion, shock, or vibration.
ADXL 335
• The module measures acceleration within range ±3g in the
Accelerometer
x, y and z axes.
• The output signals (X_OUT, Y_OUT, Z_OUT) are analog
voltages that are proportional to the acceleration.
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Interfacing ADXL 335 Accelerometer to Arduino UNO
X_OUT, Y_OUT and Y_OUT
are connected to analog
input pins.
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9
Course Name: Embedded System Design with ARM
Faculty Name: Dr. Kamalika Datta
Department : Computer Science and Engineering
Topic
Lecture 39: Experiment using Accelerometer
Experiment with Accelerometer
Demonstration
ADXL335 and STM kit connection
• Vcc – voltage source (+5V)
• GND – to ground
• X_out, Y_out, Z_out – Analogue input pins A0, A1, A2.
Connection
Diagram
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Analysis for movement along x-axis
Z Y X
Y
X Z
X value min X value max
Analysis for movement along y-axis
Z Y
X
Y Z
X
Y value min Y value max
Analysis for movement along z-axis
Y
X Z X
Y
Z
Z value min Z value max
Mbed C Code for Analysis
#include "mbed.h"
Serial pc (USBTX, USBRX);
AnalogIn x (A0);
AnalogIn y (A1);
AnalogIn z (A2);
int main() {
int x1, y1, z1;
while(1) {
x1 = x.read_u16();
y1 = y.read_u16();
z1 = z.read_u16();
pc.printf ("%d,%d,%d\n",x1, y1, z1);
wait(1);
}
}
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Printing Data to MATLAB
• The printing of data into MATLAB is similar to that for HyperTerminal software.
• MATLAB also uses serial connection to get data from serial port.
• The mbed code for reading the data from the STM32 kit is the same as shown
before.
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Complete MATLAB Code
function ploting()
TIMEOUT = 5; % time to wait for data before aborting the connection
XPOINTS = 100; % no of points along x axis
try
mbed = serial('COM3','BaudRate',9600,'Parity','none','DataBits',
8,'StopBits',1);
set(mbed,'Timeout',TIMEOUT);
fopen(mbed);
position = 1;
time = 1;
x = [(1:XPOINTS)' (1:XPOINTS)' (1:XPOINTS)'];
xlables = (1:XPOINTS);
y = zeros(XPOINTS,3);
flushinput(mbed);
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while (1)
values = fscanf(mbed,'%d,%d,%d\n');
y(position,:)=values';
xlables(position)=time;
time=time+1;
if (position < XPOINTS)
position = position + 1;
else
position = 1;
end
plot(x,y);
drawnow;
end
fclose(mbed);
catch
disp('Failed!');
fclose(mbed);
end
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Sample Output Waveform
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Course Name: Embedded System Design with ARM
Faculty Name: Dr. Kamalika Datta
Department : Computer Science and Engineering
Topic
Lecture 40: Experiment using Bluetooth
Experiment with Bluetooth and
accelerometer
Demonstration
Connection Diagram
• After this connection LED of
Bluetooth module HC-06 will start
blinking.
• When the device is connected
with any other Bluetooth device
the it will stop blinking.
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Test Program to Print using Bluetooth Module
#include "mbed.h"
Serial bluetooth(D8, D2);//RX, TX
int i=0;
int main()
{
bluetooth.printf(“Hello\n\n”);
wait(5);
bluetooth.printf(“Welcome to\n”);
bluetooth.printf(“EMBEDDED SYSTEM DESIGN WITH ARM”);
bluetooth.printf(“NPTEL-2018”);
}
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Interfacing Bluetooth and Accelerometer Modules
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Mbed C Program – Version 1
#include "mbed.h"
#include <string.h>
Serial bluetooth(D8, D2);//RX, TX
AnalogIn X(A1);
AnalogIn Y(A2);
AnalogIn Z(A3);
int main()
{
int x1, y1, z1;
while(1) {
x1 = X.read_u16();
y1 = Y.read_u16();
z1 = Z.read_u16();
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if (x1>28000 && x1<31000 && y1>35000 && y1<39000 && z1>35000 && z1<39000)
{
bluetooth.printf ("Device is vertically up \n\n");
wait(1);
}
else if (x1>42000 && x1<46000 && y1>34000 && y1<39000 && z1>34000 &&
z1<39000)
{
bluetooth.printf ("Device is verticaly down \n\n");
wait(1);
}
else if (x1>35000 && x1<39000 && y1>35000 && y1<39000 && z1>43000 &&
z1<46000)
{
bluetooth.printf ("Device is flat \n\n");
wait(1);
}
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else if (x1>34000 && x1<39000 && y1>26000 && y1<30000 && z1>34000 &&
z1<39000)
{
bluetooth.printf ("Device is horizontally left \n\n");
wait(1);
}
else if (x1>34000 && x1<39000 && y1>43000 && y1<46000 && z1>34000 &&
z1<39000)
{
bluetooth.printf ("Device is horizontally right \n\n");
wait(1);
}
wait(2);
}
}
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Mbed C Program – Version 2
#include "mbed.h"
#include <string.h>
Serial bluetooth(D8, D2);//RX, TX
AnalogIn X(A1);
AnalogIn Y(A2);
AnalogIn Z(A3);
int main(){
int flag=0;
int old_flag=0;
int x1, y1, z1;
char buf[50];
while(1) {
x1 = X.read_u16();
y1 = Y.read_u16();
z1 = Z.read_u16();
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if (x1>28000 && x1<31000 && y1>35000 && y1<39000 && z1>35000 && z1<39000) {
flag=1;
sprintf (buf, "%s", "Device is vertically up \n\n");
}
else if (x1>42000 && x1<46000 && y1>34000 && y1<39000 && z1>34000 &&
z1<39000) {
flag=2;
sprintf(buf, "%s", "Device is verticaly down \n\n");
}
else if (x1>35000 && x1<39000 && y1>35000 && y1<39000 && z1>43000 &&
z1<46000) {
flag=3;
sprintf(buf, "%s", "Device is flat \n\n");
}
else if (x1>34000 && x1<39000 && y1>26000 && y1<30000 && z1>34000 &&
z1<39000) {
flag=4;
sprintf(buf, "%s", "Device is horizontally left \n\n");
}
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else if (x1>34000 && x1<39000 && y1>43000 && y1<46000 && z1>34000 &&
z1<39000) {
flag=5;
sprintf(buf, "%s", "Device is horizontally right \n\n");
}
if (flag != old_flag) {
old_flag = flag;
blutooth.printf ("%s", buf);
wait(1);
}
wait(1);
}
}
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12
Course Name: Embedded System Design with ARM
Faculty Name: Dr. Kamalika Datta
Department : Computer Science and Engineering
Topic
Lecture 41: Experiment with Gas Sensor
Interfacing the MQ2 gas sensor to STM32
board
Demonstration
About the MQ2 Gas Sensor
• The MQ-2 gas sensor is most suited to measure the presence of the following gases:
• Methane, Butane, LPG, Smoke
• Pin configuration:
• Pin 1: Power supply voltage (typically +5V)
• Pin 2: Ground connection
• Pin 3: Digital Out – We can get a digital output from this pin, by setting a threshold value using the
potentiometer.
• Pin 4: Analog Out – This pin outputs 0-5V analog voltage based on the intensity of the gas.
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• Point to note:
• There is a heater inside the sensor, which requires 20 seconds to preheat after power is
applied.
• For interfacing with the microcontroller, the Analog Out pin can be connected to one of the
analog input pins.
• A suitable threshold can be set to trigger an alarm on detecting some gas.
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The Experiment
• When the presence of gas is detected, an audible alarm has to be sounded.
• The MQ-2 gas sensor is connected to the analog input pin A1 of the STM32F501 Nucleo board.
• A speaker is connected to the PWM digital output pin D3.
5
Connection Diagram – STM32
6
#include "mbed.h" int main()
PwmOut mypwm(D3);
Mbed AnalogIn G(A1);
{
float x;
C Code int i=0; while(1) {
x = G.read();
void fire(){ printf ("%4.2f\n",x);
i=0; if (x > 0.30)
while (i<5) { {
mypwm.period_us (3000); fire();
mypwm.pulsewidth_us (1550); wait(1);
mypwm.period_us (3000); mypwm.period_us(10);
mypwm.pulsewidth_us (1550); mypwm.pulsewidth_us(5);
wait (0.5); }
mypwm.period_us (2200); }
mypwm.pulsewidth_us (100); }
wait (0.5);
i++;
}
}
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