The Qt GUI for Arduino is an application that allows to connect Arduino Uno/Mega boards with Desktop operating systems like(Windows,Ubuntu,Macintosh)in an easy way, the communication between Arduino and computer happens over Serial Port channel.Arduino and computer are connected by USB.Arduino uses digital pins 0 (RX) and 1 (TX),for serial port communication. It is easy to create a customizable HMI(Human Machine Interface) using Qt Widgets like Slider,Dial,Label and over 50 other GUI controls available in the library. Qt Widgets can serve both as IO(Input and Output) to the Arduino, two cases are studied for visualizing the input and output data. sending serial commands from Qt GUI to Arduino,and receiving the serial stream data coming from Arduino to computer finally displaying it on Qt GUI. Case1: Qt GUI as Input to Arduino Microcontroller(Control brightness of LED.) Create a custom graphical user interface (Qt GUI), that can communicate with Arduino Serial port, and facilitate brightness control of an LED . Case 2: Qt GUI as Display screen(Ouput Device)Read RPM of a DC Motor Create a custom graphical user interface (GUI), that can communicate with Arduino by reading RPM of a Motor.By reading the serial stream data coming from Arduino to Desktop GUI can be updated with the motor RPM.

1. Arduino Qt HMI - Serial Port
A Term Paper Final Report
by
SATYENDRA KUMAR J
M. Tech. (Mechatronics) 1st semester Student
Under the supervision of
T ESHWAR RAO
ASSOCIATE PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
K L University, Green Fields,
Vaddeswaram- 522502, Guntur(Dist), Andhra Pradesh, India.
April - 2017

2. contents
• Abstract
• Introduction
• Required Setup
• Methodology
• Theory(PWM)
• analogWrite()
• Observation
• analogRead()
• Qt HMI Screens.
• References

3. Abstract
• To create customized Qt graphical user
interfaces (GUI), which facilitates brightness
control of LED, and RPM display of DC
Motor,connected to an Arduino Uno
Microcontroller.

4. Introduction
• By using the Qt's serial port functionality in
conjunction with an Arduino uno
Microcontroller (RS232 device) ,it is possible
to control the color brightness of an LED.
• similarly change the speed of a DC motor by
sending the values from a Qt GUI in a range of
0 to 255 and display the RPM of motor on the
same GUI.

5. • Serial commands can be sent from GUI (Qt)
and the same way parsing them on Arduino (at
a baud rate of 9600),communication will be
established with the Qt GUI and there to the
LED or DC Motor connected to Arduino
Microcontroller by jumper wires on a
breadboard.

6. Required Setup
• Install Qt 5.7.1.
• Serial Port Library installed on the Host
machine. (Windows/Ubuntu).
• Qt C++ based GUI screen for sending PWM
values (0 to 255).
• Resistors(300 Ω upto 1KΩ), (red, purple,
brown stripes)
• LEDs (Red, Green, Blue colors).
• DC Motor.(0to 5Volts),1000RPM.

7. • Jumper wire pack (M to M)
• BreadBoard

8. Methodology
• It is possible to control the brightness intensity
of the Red, Green, Blue lights (RGB LED)on
the Breadboard by writing code in Qt C++, and
sending commands from Qt GUI to the
Arduino microcontroller.
• So whenever there is a change in the value on
the GUI control present on the computer, the
corresponding value is sent to Arduino
microcontroller.

9. Pulse Width Modulation
• Pulse Width Modulation( PWM), is a
technique for getting analog results with digital
means, the on-off pattern can simulate voltages
in between full on (5 Volts) and off (0 Volts)
by changing the portion of the time the signal
spends on to off.
• The duration of "on time" is called the pulse
width.

10. • There are 5 pins on most Arduino boards
marked with "~" next to the pin number (on
some boards it is an “PWM” symbol).
• Pulse Width Modulation (or PWM) is a
technique for controlling power.In this case it
is used to control the brightness of LEDs.

11. • Roughly every 1/500 of a second, the PWM
output will produce a pulse. The length of this
pulse is controlled by the 'analogWrite'
function.
• By specifying a value in the analogWrite(val),
function between 0 and 255 a pulse can be
produced.

12. • If the output pulse is only high for 5% of the
time then whatever is driven will only receive
5% of full power.
• Similarly if the output pulse is high for 95% of
the time then whatever is driven will receive
95% of full power. (in this case an LED and DC
Motor).

14. • SIGNALS from one of the PWM pins on
Arduino Uno Microcontroller at different
voltages and duty cycles.
• Voltages (0V to 5V)
• Duty cycles samples (5%),(50%),and(90%).

15. • To get varying analog values, change, or
modulate, the pulse width.
• If this on-off pattern is repeated fast enough on
Arduino,with an LED,the result is as if the
signal is a steady voltage between 0 and 5v
controlling the brightness of the LED.

16. analogWrite
• 'analogWrite(0)' will not produce any pulse.
• 'analogWrite(255)' will produce a pulse that
lasts all the way until the next pulse is due.
• Values between 0 and 255 a pulse can be
produced with varying width.

18. analogRead
• The Arduino board will map input voltages
between 0 and 5 volts into integer values
between 0 and 1023.
• 'analogRead()' takes pin number starting from
0 to 5,0to 15 on Arduino Mega.
• 'analogRead(1)' returns value ranging from 0
to1023.

19. • By changing the values from 0 to 255 from Qt
GUI motor speed will vary,0 being 0 RPM and
255 at the max rpm of the DC motor.

20. Qt HMI screens

22. References
• Modeling and Simulation of Pulse-Width
Modulation Inverter
• GAI Zhi-wu 1,LI Dong-sheng 1 ,SONG Zhe-cun 1 ,MA Yong 2,YU Ji-lai 2 (1.Electromechanical
Engineering College of Northeast Forestry University,Harbin Heilongjiang 150040,China; 2.HarBin
Institute of Technology,Harbin Heilongjiang 150001,Chi
• Simulation Research of Switching Power
Supply Based on PWM
• WANG Bing,ZHANG Runhe,SUN Yanxia (Information Engineering College,Inner Mongolia
University of Technology,Hohhot,010051,China)

23. • https://forum.arduino.cc
• https://forum.qt.io