Course Name: Embedded System Design with ARM
Faculty Name: Prof. Indranil Sen Gupta
Department : Computer Science and Engineering
Topic
Lecture 30: Design of Control Systems
Closed loop control system
ON-OFF controller
PID controller
Introduction
• In many embedded system applications, we have to sense the value of some
external parameter and take corrective actions to maintain it within acceptable
limits.
• Temperature of an oven, speed of a motor, etc.
• Essentially a control system.
• Two types of control systems:
a) Open loop: where there is no feedback with respect to the measured value.
b) Closed loop: more sophisticated, corrective actions applied with feedback.
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Closed Loop Control System
Comparator
Goal Forward Path Output
Feedback Path
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Role of the Controller
Control
Error Signal Output
Setpoint – Controller SYSTEM
Measured Quantity
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Examples Forward Path
Required Actual
speed Motor speed
Speed Sensor
Forward Path
Feedback Path
Required Actual
temperature Heater temperature
Temperature
Sensor
Feedback Path
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Choice of Controller Type
a) ON-OFF Controller:
• An ON-OFF controller is the simplest type of controller, where the
control signal has only two levels.
• For example, in a heater, if the actual temperature is less than the set
temperature, the heater is turned ON; otherwise, it is turned OFF.
• This type of controller is inexpensive, but often causes oscillation in the
output variable.
• It is often used in simple appliances such as oven, iron, refrigerators,
etc. where oscillations can be tolerated.
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b) Proportional (P) Controller:
• The control signal is set to be proportional to the difference between the actual output and
the setpoint (i.e. the error).
• Need to find out the value of constant of proportionality.
• Tuning the controller is a hard job.
• Typically, a P controller decreases response time, but increases overshoot.
Control
Signal Output
Error
Setpoint – Controller αe SYSTEM
e
Measured Quantity
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c) Proportional-Derivative (PD) Controller:
• To reduce the overshoot, we can take into account how fast we are approaching the setpoint.
• We add D control in addition to P control.
• D is estimated as the difference between the current measure and the previous measure.
• PD controllers are slower than P controllers, but generates less oscillation, and smaller
overshoot/ripple.
• Drawback:
• Output is close to the setpoint, and so the error is very small.
• Errors add up over time; we can define the integral (I) of the error:
Σtime (setpoint – output)
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d) Proportional-Integral-Derivative (PID) Controller:
• This is most powerful, but also the most difficult to tune.
• Once we can set the parameters properly, it gives very good performance.
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To Summarize
Controller Response Time Overshoot Error
ON-OFF Smallest Highest Large
Proportional Small Large Small
Integral Decreases Increases Zero
Derivative Increases Decreases Small change
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Course Name: Embedded System Design with ARM
Faculty Name: Prof. Indranil Sen Gupta
Department : Computer Science and Engineering
Topic
Lecture 31: Experiments with Relay
Relay interfacing
Experiments with relay interface
Demonstration
About the SRD-05DC-SL-C Relay
• Can be controlled using a 0V – 5V digital signal.
• The output load can be 10A, 250VAC.
• It is an electro-mechanical relay, with two states.
Normally Closed (NC)
Common (C)
Normally Open (NO) GND
+5V
Signal
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Connection Diagram
GND NC
+5V C
STM32F401 RE RELAY
D3 NO
Nucleo Board
Signal
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Experiment 1
• Interface an electric bulb through relay, and switch it ON and OFF under program control through
digital output port.
• The relay is controlled by the digital output line D3 of the STM32 board.
• The program turns ON the bulb for 2 seconds, turns it OFF for 5 seconds, and repeats it in a
loop.
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Mbed C Code
// Turn on a bulb for 2sec and off for 5sec repeatedly through a
// relay, which is controlled by digital port line D3.
#include "mbed.h"
DigitalOut relay (D3);
int main() {
while(1) {
relay = 1; // Turn ON bulb, and wait for 2 sec
wait(2.0);
relay = 0; // Turn OFF bulb, and wait for 5 sec
wait(5.0);
}
}
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Experiment 2
• Interface an electric bulb through relay, and vary its brightness under program control through
PWM port.
• The circuit connection remains the same, but now the digital port D3 is used with PWM
control.
• By changing the duty cycle, the brightness of the bulb can be controlled.
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Mbed C Code for STM32
#include "mbed.h"
PwmOut bulb (D3); // D3 is set as a PWM controlled digital output
int main() {
bulb.period (0.02); // PWM period 20 msec
while(1) {
bulb.write (1.0); // duty cycle = 1.0;
wait (3.0); // wait for 3 second
bulb.write (0.8); // duty cycle = 0.8;
wait (3.0); // wait for 3 second
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Mbed C Code
bulb.write (0.6); // duty cycle = 0.6;
wait (3.0); // wait for 3 second
bulb.write (0.4); // duty cycle = 0.4;
wait (3.0); // wait for 3 second
bulb.write (0.2); // duty cycle = 0.2;
wait (3.0); // wait for 3 second
bulb.write (0.0); // duty cycle = 0.0;
wait (3.0); // wait for 3 second
}
}
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Experiment 3
• Interface an electric bulb through relay, and turn it ON or OFF depending on ambient light as
sensed using a LDR.
• The relay is connected through digital output pin D3 as usual.
• A LDR light sensing circuit, that generates an analog output voltage, is connected to the
analog input pin A1.
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Connection Diagram
GND NC
+5V C
STM32F401 RE RELAY
D3 NO
Nucleo Board
Signal
A1
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#include "mbed.h"
PwmOut bulb (D3); // D3 is set as a PWM controlled digital output
AnalogIn ldr (A1); // LDR circuit output is connected to pin A1
Mbed C
int main()
{
Code
float light;
int value;
bulb.period (0.02);
while(1) {
light = ldr.read();
value = light * 5000;
if (value > 4000)
bulb.write (0.0);
else
bulb.write (1.0);
}
}
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Course Name: Embedded System Design with ARM
Faculty Name: Prof. Indranil Sen Gupta
Department : Computer Science and Engineering
Topic
Lecture 32: Experiments on Speed Control of DC Motor
Motor interface and speed sensing
Experiments with motor interface
Demonstration
About the Motor Interface and Speed Sensing Slots
• A DC motor is used, where the rotating shaft is connected to a metal wheel
cut with 8 slots.
• The wheel is attached to an optocoupler circuit, which generates optical
interruptions whenever the wheel rotates.
• 8 optical interrupts for every single rotation of the wheel.
• An optocoupler circuit generates a pulse for every interruption.
Optocoupler
• How is the motor driven?
• Directly from the PWM port of the microcontroller.
• By changing the PWM duty cycle, the speed of the motor can be varied.
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MOC7811
Optocoupler
Sensing Optical
Interruptions
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Connection Diagram – STM32
PWM/D3
GND
+5 V STM32F401RE
D4
GND
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Experiment 1
• Interface the motor and a push switch. On successive presses of the switch, the
following will alternate repeatedly:
a) Run the motor at high speed +5V
b) Run the motor at low speed
c) Turn off the motor
• The push switch is interfaced to D2
port line D2.
• PWM control is used to drive
the motor.
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Embed C Code – STM32
#include "mbed.h"
PwmOut motor (D3); // D3 is set as a PWM controlled digital output
DigitalIn push_switch (D2); // Switch output is connected to pin D2
int main()
{
int state = 1;
motor.period (0.10);
motor = 1.0; // Duty cycle = 1.0
while(1) {
if (push_switch == 0) { // Check for switch press
state++;
if (state == 4) state = 1;
}
while (push_switch == 0) ; // Wait for key release
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switch (state) { // Set duty cycle depending on state
case 1: motor = 1.0;
break;
case 2: motor = 0.8;
break;
case 3: motor = 0.0;
break;
}
}
}
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Experiment 2
• Interface the motor and read the pulses generated by the rotary sensor. Count
the pulses and display the RPM on a LCD display unit.
• The pulses generated by the
optocoupler are fed to interrupt
input D4.
• PWM control is used to drive
the motor.
• LCD display unit is also
interfaced.
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Embed C Code – STM32
#include "mbed.h"
#include "TextLCD.h"
#include "TextLCDScroll.h"
PwmOut motor (D3); // D3 is set as a PWM controlled digital output
InterruptIn wheel (D4); // Optocoupler output is connected to pin D4
TextLCDScroll lcd(D13, D12, D11, D10, D9, D8, TextLCD::LCD16x2);
int pulses = 0;
void count()
{
pulses = pulses + 1;
}
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Embed C Code – STM32
int main()
{
int RPM; char msg[20];
wheel.rise (&count);
motor.period (0.10);
motor = 0.9;
lcd.cls();
while (1) {
wait (1.0);
RPM = pulses * 60 / 8; // In a minute; 8 slots in the wheel
sprintf (msg, "%6d", RPM);
lcd.setLine (0, "The RPM is:");
lcd.setLine (1, msg);
pulses = 0;
}
}
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Course Name: Embedded System Design with ARM
Faculty Name: Prof. Indranil Sen Gupta
Department : Computer Science and Engineering
Topic
Lecture 33: Experiment with Multiple Sensors and Relay
Interfacing multiple sensor and multiple
output devices
Demonstration
Introduction
• In this experiment, we shall consider the interfacing of multiple sensors and multiple output
devices.
• Input devices: LDR, LM35 temperature sensor
• Output devices: Relay driving a bulb, Speaker
• We shall demonstrate how the same microcontroller can be used to perform multiple tasks in a
time multiplexed way.
• The experiment is also realistic enough such that it can be related to practical scenarios of home
automation.
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The Experiment
Interface relay, speaker, LDR, and LM35 to the STM32F401 Nucleo board:
• The relay circuit is used to drive a bulb (driven by D3).
• The speaker is interfaced to generate an audible output (driven by D5 using PWM).
• The LDR circuit is used to sense the level of ambient light (connected to A1).
• The LM35 sensor is used to measure the temperature (connected to A0).
• If the ambient light falls below a threshold, the bulb will turn on.
• Whenever the temperature crosses a threshold, an alarm will sound.
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Connection Diagram
+5V A0
GND NC
+5V C
STM32F401 RE RELAY
D3 NO
Nucleo Board
Signal
GND D5/ A1
PWM LDR
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Basic Program Logic
• The steps as shown must begin
run in a repetitive loop. if (value(A0) > thres_light)
• There can be a delay D3 = 0; // Turn OFF relay (bulb)
else
before the loop repeats.
D3 = 1; // Turn ON relay (bulb)
• First, the LDR generated if (value(A1) > thres_temp)
sensor voltage is read D5 = PWM tone; // Turn ON alarm
through A0. else
• Then, LM35 generated D5 = No PWM tone; // Turn OFF alarm
temperature data is read end
through A1.
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Mbed C Code for STM32F401
#include "mbed.h"
PwmOut bulb (D3); // Relay connected to PWM output D3
PwmOut speaker (D6); // Speaker connected to PWM output D5
AnalogIn ldr (A1); // LDR circuit output is connected to pin A1
AnalogIn lm35 (A0); // LM35 output is connected to pin A0
int main()
{
float light, temper;
int lvalue, tvalue;
bulb.period (0.02);
speaker.period_ms (3);
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while(1) {
light = ldr.read(); // First sense the ambient light
lvalue = light * 5000;
if (lvalue > 4000) // Turn on bulb if required
bulb.write (0.0);
else
bulb.write (1.0);
temper = lm35.read(); // Next sense the temperature
tvalue = temper * 1000;
if (tvalue > 96) { // Generate fire alarm if required
speaker = 0.5; // 333 Hz, 50% duty cycle tome
}
else {
speaker.period_us (3000);
speaker = 0.0; // 0% duty cycle (NO TONE)
}
}
}
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