==== IB3: PWM mode (~) of digital pins, programming threshold values ====
=== Target group ===
This hands-on lab guide is intended for the Beginners but other target groups may benefit from it, treating it as a tool for advanced projects.
=== Prerequisites ===
== Liquid Crystal ==
For this library, you may refer to the [[en:iot-open:remotelab:ume:smartme:b1|B1 exercise]].
== RGB LED ==
The SmartME Network Laboratory Arduino nodes 1-5 are equipped with an RGB LED.
To connect other devices, however, only the green light component is available, exposed as a separate LED.
To turn on the green LED, you have to follow three steps:
- first, you have to define a variable with the number of the pin where the LED is connected to (int greenPin = 3;);
- second, you need to configure this variable in output mode (OUTPUT) by invoking the pinMode(pin, mode) function, inside the setup() function.
- finally, you need to send to this variable a HIGH signal by using the digitalWrite(pin, value) function, inside the loop() function.
To turn off the LED, you need to send a LOW signal value to this pin.
You can make the LED flashing by tuning the delay of HIGH and LOW states.
The digital pins either give you 5V (when turned HIGH) or 0V (when turned LOW) and the output is a square wave signal.
PWM stands for Pulse Width Modulation and it is a technique used in controlling the brightness of the LED. The PWM pins are labelled with ~ sign.
The function analogWrite() can be used to generate a PWM signal in those digital pins that are labelled with ~ sign. The frequency of this generated signal for most pins will be about 490Hz and you can give the value from 0-255 using this function
* analogWrite(0) means a signal of 0% duty cycle.
* analogWrite(127) means a signal of 50% duty cycle.
* analogWrite(255) means a signal of 100% duty cycle.
The function random() generates pseudo-random numbers. The syntax is random(max) or random(min, max), where min represents the lower bound of the random value, inclusive (optional); and max represents the upper bound of the random value, exclusive. The function returns a long random number between min and max-1.
== The circuit: ==
RGB GREEN pin = Arduino pin 3 (~)
=== Scenario ===
Initialize the LCD screen with the label “rand value”, then calculates a random value. If randomValue is lower than lowThreshold, turn on the LED. If randomValue is upper than highThreshold, turn off the LED. After 1 second, print the random value to the LCD. Then, turn on the LED for 3 seconds, assigning it a value of brightness which corresponds to the random value previously calculated. Note, you can set the two values of the threshold as you prefer. You can modify the brightness of the LED because, although it is connected to a digital pin, the Arduino pin number 3 is labeled with ~ sign (PWM).
=== Result ===
You should see the LED on or off for 1 second, a second if the value is greater or less than the predefined threshold values. Next, you should see the randomly calculated value between 0 and 255 on the LCD, at that point, the LED should assign a brightness associated with that value, and keep it for 3 seconds.
=== Start ===
There are no special steps to be performed.
=== Steps ===
== Step 1 ==
Include the LCD driver library:
#include
== Step 2 ==
Instantiate the software controller component for the LCD display. Initialize the LED pin. Declare the threshold values.
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 6, 5, 4, 13, 2);
// initializing LED Pin
int greenPin = 3;
// declaring the threshold values
int lowThreshold = 127;
int highTreshold = 128;
== Step 3 ==
Initialize the display and declare the LED pin as OUTPUT - preferably in the setup() function:
void setup(){
pinMode(greenPin, OUTPUT); // declaring LED pin as output
lcd.begin(16, 2); // set up the LCD's number of columns and rows
lcd.print("rand value"); // print the random value label to the LCD
}
== Step 4 ==
Implement loop() to do in the order:
calculate a random value between 0 and 255;
compare the random value with the lower threshold and with the upper threshold in order to decide whether to switch the LED on or off for 1 second;
display the random value on the screen, and use it to assign a specific brightness value to the LED, which must be held for 3 seconds.
void loop() {
// calculate a randomValue in the range 0-255
int randomValue = random(255);
if (randomValue < lowThreshold){
digitalWrite(greenPin, HIGH);
}
if (randomValue > highTreshold){
digitalWrite(greenPin, LOW);
}
delay(1000); // print the random value of light to the LCD
lcd.setCursor(14, 0);
lcd.print(randomValue);
analogWrite(greenPin, randomValue);
delay(3000);
}
=== Result validation ===
The state of the LED will depend on the random number calculated and on the threshold values that have been set.
The random value will be shown by the display monitor.
It also will affect the LED brightness for 3 seconds.
=== Platformio.ini ===
[env:uno]
platform = atmelavr
board = uno
framework = arduino
lib_ldf_mode=deep+
lib_compat_mode=strict
lib_deps =
DHT sensor library@1.3.0
Adafruit Unified Sensor@1.0.3
lib_deps_external =
https://github.com/arduino-libraries/LiquidCrystal.git#1.0.7
=== IB3.cpp ===
#include
#include "DHT.h"
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 6, 5, 4, 13, 2);
// initializing LED Pin
int greenPin = 3;
// declaring of threshold values
int lowThreshold = 500;
int highTreshold = 600;
void setup(){
// declaring LED pin as output
pinMode(greenPin, OUTPUT);
// set up the LCD's number of columns and rows
lcd.begin(16, 2);
// print the random value label to the LCD
lcd.print("rand value");
}
void loop() {
int randomValue = random(255);
if (randomValue < lowThreshold){
digitalWrite(greenPin, HIGH);
}
if (randomValue > highTreshold){
digitalWrite(greenPin, LOW);
}
delay(1000);
// print the random value of light to the LCD
lcd.setCursor(14, 0);
lcd.print(randomValue);
analogWrite(greenPin, randomValue);
delay(3000);
}