Flags

Flags are a little like switches that trigger different events in your program depending on whether they’re on (a value of 1) or off (a value of 0). One way to think of it is like the flags on mailboxes. If the flag is up, that means the mail carrier has something to pick up. If the flag is down, that means there is nothing for the mail carrier to pick up.

In programming, flags are usually used with if, else if, and else statements, with the flag as the conditional and the event as the action that will be performed if the statement is true.

if (flag == 0){
    event 1;
}

else if (flag == 1){
    event 2;
}

For this program, if the flag has a value of 0, event 1 will happen. If the flag has a value of 1, event 2 will happen.

Flags are variables that perform a specific function, and just like any other variable, you need to initialize it in your program before you can use it. After including your CoDrone library, declare these variables in Arduino:

#include<CoDrone.h>

int move_flag;
int fly_flag;
int counter;

Next, in void setup, you’re going to connect your drone, change the drone mode to flight, and set all of the variables’ values to 0.

void setup() {
 CoDrone.begin(115200);
 CoDrone.pair();
 CoDrone.DroneModeChange(Flight); 
 
 move_flag = 0;
 fly_flag = 0;
 counter = 0;
}

Really quick detour: counters are a way to break your code up into steps and keep track of which step you’re on. Just like flags, you need to set them up as a variable at the beginning of your program (which you did during the last step), and you can use them with if, else if, and else statements.

This is what a counter program usually looks like:

int counter = 0; 
void setup(){
}
void loop(){
  if (counter == 0){
    // code for step 1
    counter = 1;
 }
  else if (counter == 1){
    // code for step 2
    counter = 2;
  }
  else if (counter == 2){
    // code for step 3
    counter = 3;
  }
}

You only need to use one sensor in your program, and that’s going to be sensor 11! In void loop, initialize sensor 11 as an input, and then write your program so that if sensor 11 is triggered (which means you’re covering it), your CoDrone will stop.

You’re probably thinking, “But Robolink! It hasn’t even taken off yet! Why would it stop?!” This is mostly so your CoDrone doesn’t immediately hit the ceiling once you cover sensor 11. For your next line, you’re going to include a delay of 1 second and then have the counter add 1 to itself after that second is up. We promise something will happen in the next step.

void loop() {
 byte bt1 = digitalRead(11);

 if( bt1 ){
   CoDrone.FlightEvent(Stop); 
   CoDrone.move(1);
   counter++;
 }

Remember that we said that a value of 1 would be added to the counter every second that sensor 11 was triggered? This is where your flags will start to come together with the counter!

First, create an if statement so that if the counter is 3, fly_flag is 1. Don’t worry, we’ll talk about what fly_flag is in the next step, but you can guess in the meantime!

Next, create an if statement so that if the counter is 6, move_flag is 1. Again, next step, you can guess.

Finally, create another if statement so that if the counter is 9, your CoDrone lands. Wait! It didn’t even take off yet! What happened?! Again, we’ll explain in the next step.

if(counter == 3){
   fly_flag = 1;
 }
 if(counter == 6){
   move_flag = 1;
 }
 if(counter == 9){
   CoDrone.setPitch(0);
   CoDrone.move(0.5);
   CoDrone.land();
 }

If you guessed that fly_flag means that the CoDrone is going to fly, you were right! Write an if statement so that if the value of fly_flag is 1, the CoDrone will take off and play a sound on the buzzer. Make sure you include a line that changes the value of fly_flag back to 0 so that the CoDrone only takes off once and doesn’t hit the ceiling.

If you guessed that move_flag means that the CoDrone is going to move, you were right! Write an if statement so that if the value of move_flag is 1, the CoDrone will pitch forward at 50 and play a sound on the buzzer.

if(fly_flag == 1){
   CoDrone.takeoff();
   fly_flag = 0;
   CoDrone.Buzz(400,4);
 }

 if(move_flag == 1){
   CoDrone.setPitch(50);
   CoDrone.Buzz(400,4);
 }

This is what your final code should look like:

#include<CoDrone.h>

int move_flag;
int fly_flag;
int counter;

void setup() {
 CoDrone.begin(115200);
 CoDrone.pair();
 CoDrone.DroneModeChange(Flight); 
 
 move_flag = 0;
 fly_flag = 0;
 counter = 0;
}

void loop() {
 byte bt1 = digitalRead(11);
 
 if( bt1 ){
   CoDrone.emergencyStop(); //kill switch
   CoDrone.move(1);
   counter++;
 }

 if(counter == 3){
   fly_flag = 1;
 }

 if(counter == 6){
   move_flag = 1;
 }

 if(counter == 9){
   CoDrone.setPitch(0);
   CoDrone.move(0.5);
   CoDrone.land();
 }

 //flag trigger takeoff the drone
 if(fly_flag == 1){
   CoDrone.takeoff();
   fly_flag = 0;
   CoDrone.Buzz(400,4);
 }

// move trigger make drone go forward
 if(move_flag == 1){
   CoDrone.setPitch(50);
   CoDrone.move();
   CoDrone.Buzz(400,4);
 }
 
}