Introduction to IoT
LAB Exercises
Karel Slavicek
Vaclav Oujezsky
2024
IoT LAB - Outline
●
Rotary encoder
●
PWM modulation (if can fit in)
Hardware Overview
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MCU board - STM32
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Communication board – CANbus
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Application board - LCD
LCD
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Liquid Crystal Display
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Invented in 1964
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Used to display information
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Various modes of operation
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Used in
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Watches
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Laptops
●
Phones
Using LCD
●Libraries
○https://github.com/johnrickman/LiquidCrystal_I2C/tree/c976ad2dc682d40d994797761f39d4d9f0cc8196
●Include the libraries
○Wire.h to use I2C
○#include <Wire.h>
○#include <LiquidCrystal_I2C.h>
●Initialize LCD
○16 x 2 LCD
○Using 0x3F I2C address
○LiquidCrystal_I2C oLcd(0x3F, 16, 2);
○oLcd.init();
○oLcd.backlight();
○oLcd.setCursor(0, 0);
●Functions available
○oLcd.clear();
○oLcd.print(“Hello world");
○oLcd.setCursor(0, 1);
LCD
●
Serves as supportive tool today, we focus on the rotary
encoder
●
Will be discuse in more detailes later
Rotary encoder – how it works
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When you turn the knob, A and B make contact with
the common ground pin C in a specific order
HW structure
STM32 pinout
Rotary encoder pinout
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#define CLK PB4
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#define DT PB5
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#define BTN PA15
Using rotary encoder
void setup() {
// Set encoder pins as inputs
pinMode(CLK,INPUT);
pinMode(DT,INPUT);
pinMode(SW, INPUT_PULLUP);
// Setup Serial Monitor
Serial.begin(9600);
// Read the initial state of CLK
lastStateCLK = digitalRead(CLK);
}
Using rotary encoder
void loop() {
// Read the current state of CLK
currentStateCLK = digitalRead(CLK);
// If last and current state of CLK are different, then pulse occurred
if (currentStateCLK != lastStateCLK && currentStateCLK == 1){
// If the DT state is different than the CLK state then the encoder is rotating CCW so decrement
if (digitalRead(DT) != currentStateCLK) {
counter --;
currentDir ="CCW";
} else {
counter ++;
currentDir ="CW";
}
Serial.print("Counter: ");
Serial.println(counter);
}
Using rotary encoder
// Remember last CLK state
lastStateCLK = currentStateCLK;
// Read the button state
int btnState = digitalRead(SW);
if (btnState == LOW) {
if (millis() - lastButtonPress > 50) {
Serial.println("Button pressed!");
}
// Remember last button press event
lastButtonPress = millis();
}
delay(1);
}
Interrupts
●
Why do we need interrupts?
●
How it works?
Rotary encoder with interrupts
int counter = 0;
int currentStateCLK;
int lastStateCLK;
String currentDir = "";
unsigned long lastButtonPress = 0;
void setup() {
pinMode(CLK, INPUT);
pinMode(DT, INPUT);
pinMode(BTN, INPUT_PULLUP);
lastStateCLK = digitalRead(CLK);
oLcd.init();
oLcd.backlight();
oLcd.setCursor(0, 0);
attachInterrupt(CLK, updateEncoder, CHANGE);
attachInterrupt(DT, updateEncoder, CHANGE);
attachInterrupt(BTN, updateBtnPressed, CHANGE);
}
Rotary encoder with interrupts
void updateEncoder(){
currentStateCLK = digitalRead(CLK);
if (currentStateCLK != lastStateCLK && currentStateCLK == 1){
if (digitalRead(DT) != currentStateCLK) {
counter --;
currentDir ="CCW";
} else {
counter ++;
currentDir ="CW";
}
oLcd.clear();
oLcd.print("Direction: ");
oLcd.print(currentDir);
oLcd.setCursor(0, 1);
oLcd.print("Counter: ");
oLcd.print(counter);
}
lastStateCLK = currentStateCLK;
}
Now it is the time for
your own experiments!