『EP1000 DIGI FABLAB』

Input devices

Input devices, also called sensors detect events or changes in its enviroment and sends information to other electronics. Most sensors give out analog signals (potentiometer, LDR, Water sensor, etc). Digital sensors transmits data in digital directly, like push buttons.

In this project, we are to control 2 LEDs with a push button using an Arduino UNO.

The LED's should turn on in this sequence:

• Initially, LEDs are all in the OFF state.
• Pressing the switch, turns on only the RED LED.
• Pressing the switch again, turns on only the GREEN LED
• Pressing the switch again, turns on all LEDs
• Pressing the switch again, turns off all LEDs returning to the first state.

First of all I design the circuit on ThinkerCAD:

For the resistor values I used 200 ohm resistors connected to the LED and a 1k ohm resistor connected to the push button switch. The bush button is set up in active-high arrangement, meaning when the button is pressed a low signal (low voltage) will be sent to the pin input.

Another important thing to note is the pin output (positive) is connected to the LED anode. There are multiple methods of identifying the anode and cathode of an LED, such as the longer leg usually indicates the anode, or looking at the LED body, the leg closer to the flat edge indicates the cathode. Another easier way is running a small voltage through the LED, the anode must be connected the the positive and the negative connected to the cathode. Connecting it in reverse may damage it!

Then I write, test and troubleshoot the program on the website.

Here is the final program:

const int LED = 9;
  const int LED2 = 10;
  const int SW = 4;
  int lastSWstate;
  int count = 0;
  
  void setup(){
    pinMode(LED, OUTPUT);
    pinMode(LED2, OUTPUT);
    pinMode(SW, INPUT);
    lastSWstate = HIGH; 
  }
  void loop(){
    int reading = digitalRead(SW);
    if (reading == LOW){
      if (lastSWstate == HIGH){ //if button press
        count++;
        lastSWstate = LOW;
    }
    }
    else lastSWstate = HIGH;
    
    if (count ==0){
    digitalWrite(LED, LOW);
      digitalWrite(LED2, LOW);
    }
    else if (count == 1){
      digitalWrite(LED, HIGH);
      digitalWrite(LED2, LOW);
    }
    else if (count == 2){
    digitalWrite(LED, LOW);
      digitalWrite(LED2, HIGH);
    }
     else if (count == 3){
    digitalWrite(LED, HIGH);
      digitalWrite(LED2, HIGH);
    }
    else{
      count = 0 ;
    }
  }

Note that I changed the pin numbers on the actual board compared to the ThinkerCAD simulator for a more neater circuit layout on the breadboard.

The program works by counting the number of times the button has been pressed, where for the number of times counted will toggle the state of the LEDs using if-else statements.

After testing on ThinkerCAD I recreate the circuit physically and upload the program on the arduino UNO.

Analog inputs

While digital signals are discrete and changes in specific steps (High and Low), analog signals can vary continuously.

Arduino UNO has 6 analog pins A0-A5, which are used when interfacing analog input devices such as potentiometers, LDR (Light dependent resistors) and other sensors.
It uses an ADC (Analog to Digital Convertor) to convert an input voltage into a number, requiring a reference voltage and a n-bit ADC.

As Arduino does not have a built in DAC (Digital to Analog Convertor), we will use PWM (pulse width modulation) to vary the output voltage.
It works by modulating the width of the pulse of a square wave, changing its average voltage. A square wave thats high 50% of the time will have a 50% duty cycle PWM, while a continuous high output will be a 100% duty cycle.

The Arduino has 6 PWM ports, which has a "~" at the end of each number (3, 5, 6, 9, 10, 11)

Potentiometer and LED
The potentiometer controls the brightness of the LED.

I start by designing and programming the circuit on ThinkerCAD.

With the oscilloscope connected to the output you can view the PWM signal.

Code:

void setup()
{
  Serial.begin(9600);
  Serial.println("ready");
}

void loop()
{
  int reading = analogRead(A2);
  Serial.print("Reading = ");
  Serial.println(reading);
  delay(500);
  
  int digValue = map(reading, 0, 1023, 0, 255);
  analogWrite(9, digValue);
  Serial.print("\t");
  Serial.println(digValue);
  delay(500);
  
}

After which I implement on the physical breadboard.

You can see the change in output from the serial monitor:

Controlling a RGB LED

The circuit design I used.

• With LDR (Light Dependent Resistor)
  

The LDR resistance changes with the light intensity that falls on it. The program causes the RGB LED to change colour as light intensity detected by the LDR changes.

• With Potentiometer
  

Using the same program, I swapped the LDR with a potentiometer, so you can control the colour of the LED by turning the knob.

Output devices

Output devices, also known as actuators are components that move, control or display information. The behavior of output devices are determined by input devices.

Actuators can create movement with Stepper motors, servo motors and DC motors. Actuators that requires to display information can be LED displays, LCD displays and other light output devices. Actuators requiring control can be Relays and transistor drivers to drive high power circuits.

Servo motor control knob

I interface a potentiometer to control the rotation of a positional servo motor.

The connection is simple: Potentiometer is connected to pin A0 and Servo motor connected to analog pin 9.

Program:

#include <Servo.h>

Servo servo1;  

int potpin = 0;  
int val;    

void setup() {
  servo1.attach(9);  
}

void loop() {
  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 0, 180);     // scale it to use it with the servo (value between 0 and 180)
  servo1.write(val);                  // sets the servo position according to the scaled value
  delay(15);                           // waits for the servo to get there
}