Question

With an Arduino Uno:

Using 2 external buttons b0 and b1 to represent ‘0’ and ‘1’, design a sequence detector to detect a pattern “1101”. An LED lights up once, when the sequence “1101” occurs.

Answer 1

// A flag variable is used to verify the sequence is correct. flag is incremented at each correct input.
int flag = 0;

int check(int x,int y)
{
switch(flag)
{
    case 0 : {
              if(y==1 && x==1) //evaluates true when b1 is pressed
              {
                flag =1;        // 1 detected
              }
              else flag = 0;
              break;
    }
    case 1 : {
              if(y==1 && x==1) //evaluates true when b1 is pressed
              {
                flag = 2;       // 1 detected
              }
              else flag = 0;    // 0 detected
              break;
    }
    case 2 : {
               if(y==0 && x==0) //evaluates true when b0 is pressed
               {
                flag = 3;       // 0 detected
               }
               else if(y==1 && x==1) //evaluates true when b1 is pressed
               {
                flag = 2;       // 1 detected, Now sequence is '111....' Hence flag =2;
               }
               else ;
               break;
    }
    case 3 : {
              if(y==1 && x==1) //evaluates true when b1 is pressed
              {
                flag = 4;       // 1 detected
              }
              if(y==0 && x==0) //evaluates true when b0 is pressed
              {
                flag = 0;       // 0 detected
              }
              break;
    }
}
if(flag==4)
{
digitalWrite(3,HIGH);         // LED set to high
delay(2000);
digitalWrite(3,LOW);         // LED set to low
flag=2;                       //'1101' detected. If las one has to be taken as 1st input of following sequnece keep it. Else if you want to start fresh, change value of flag to 0.
}

return 0;
}

void setup() {

//let the inputs be connected at pin 0,1
//note that PIN0 represents b0 which signifies '0' and hence should be pulled up using a resistor to +5V. This is necessary to identify a change from high level(5V) to low level(0).
//note that PIN1 represents b1 which signifies '1' and hence should be pulled down using a resistor to ground. This is necessary to identify a change from low level(0V) to high level(5V).
pinMode(0,INPUT);
pinMode(1,INPUT);

//let the LED be connected to pin 3
pinMode(3,OUTPUT);

}

void loop() {
//receive inputs and check whether the sequence is 1101

int x = digitalRead(0); //evaluates 0 when b0 is pressed and 1 when not pressed
delay(500);              // avoid debouncing
int y = digitalRead(1); //evaluates 1 when b1 is pressed and 0 when not pressed
delay(500);              // avoid debouncing

check(x,y);
}

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PROGRAM ENDES ABOVE LINE. BELOW IS THE HARDWARE IMPLEMENTATION ONLINE.