Timers

Arduino has two timer functions: millis(), which measures milliseconds, and micros(), which measures microseconds. There are 1,000 milliseconds in 1 second and 1,000,000 microseconds in 1 second.

Both functions work exactly the same way — like stopwatches. As soon as the Smart Inventor Board is on, they start measuring the number of milliseconds or microseconds that pass by. Even if you don’t use a timer function in your program, the timer is still going on in the background!

The millis() function is the more commonly used timer, so you’re going to be using that in your CoDrone programs. Just so you can see how quickly milliseconds pass by, upload this code into a new sketch in Arduino, connect your remote, and open up the serial monitor.

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println(millis());
}

Like we said, the one problem with the millis() function: it only tells you the time from when the program was started, which is usually when the Smart Inventor Board was turned on. That means that if you have a code like the one below, which has your CoDrone taking off at 1000 milliseconds, you will never see your drone take off because it takes more than 1000 milliseconds to establish communication and connect!

void loop() {
  if (millis() < 1000) {
    CoDrone.setThrottle(70);
  }
  else {
    CoDrone.emergencyStop();
  }
}

To work around this timer issue, you can use a global variable called StartTime, another global variable called StartFlag, subtraction, and flags! To set up your code, include the CoDrone library and make sure StartTime is an unsigned long variable. Next, in void setup, establish communication, connect to a nearby drone, and have it take off for 2 seconds.

#include <CoDrone.h>

unsigned long StartTime;
int StartFlag;
 
void setup() {
  CoDrone.begin(115200);
  CoDrone.pair();

  CoDrone.takeoff();   
}

Quick explanation about how StartTimewill work with this code: you’ll be using StartTime = millis()with a flag so the timer only starts when the flag is on. Next, you’ll include lines so that the start time will be subtracted from the current milliseconds to give you a true idea of how much time has passed. Check the images below for another explanation!

Like we said in the last step, the timer will turn on when StartFlag is triggered. That will happen when sensor 11 is covered. To set that up, include the following block of code in void loop:

void loop() {
  byte bt1 = digitalRead(11);
  byte bt4 = digitalRead(14);
  byte bt8 = digitalRead(18);

  if (bt1) {
    StartTime = millis();
    StartFlag = 1;
  }

Once you set up the if statement for when the flag is triggered, you can add events! To do this, you just need to use if, else if, and else statements. However, you will also need to include the times using the current timer value minus the start time’s value.

if (StartFlag == 1) {
    if (millis() - StartTime < 2000) {
      CoDrone.setThrottle(30);
      CoDrone.move();
    }
    else if (millis() - StartTime < 5000) {
      CoDrone.setPitch(70);
      CoDrone.setThrottle(0);
      CoDrone.move();
    }
    else if (millis() - StartTime < 7000){
      CoDrone.setRoll(40);
      CoDrone.setPitch(0);
      CoDrone.move();
    }
}

You can always add more else if statements if you want to add more flight events, but when you’re ready for your CoDrone to land, you can just turn StartFlag off!

else { 
  CoDrone.land();
  StartFlag = 0;
}

Just because you’re using timers and flags does not mean you get to drop the kill switch from your program! Include this after the landing statement:

if (bt8) {
  CoDrone.emergencyStop();
  StartFlag = 0;
}

Your final code should look like this:

#include <CoDrone.h>

unsigned long StartTime;
int StartFlag;
 
void setup() {
  CoDrone.begin(115200);
  CoDrone.pair();

  CoDrone.takeoff();   //take off and hover for 3 seconds 
  CoDrone.move(3);
}

void loop() {
  byte bt1 = digitalRead(11);
  byte bt4 = digitalRead(14);
  byte bt8 = digitalRead(18);
    
  //button trigger timer
  if (bt1) {
    StartTime = millis();
    StartFlag = 1;
  }

 //as time increases, the CoDrone will go up-> forward-> right-> landing
 if (StartFlag == 1) {
    if (millis() - StartTime < 2000) {
      CoDrone.setThrottle(30);
      CoDrone.move();
    }
    else if (millis() - StartTime < 5000) {
      CoDrone.setPitch(70);
      CoDrone.setThrottle(0);
      CoDrone.move();
    }
    else if (millis() - StartTime < 7000){
      CoDrone.setRoll(40);
      CoDrone.setPitch(0);
      CoDrone.move();
    }
    else {
      CoDrone.land();
      StartFlag = 0;
    }
  }
  
  if (bt8) {
     CoDrone.emergencyStop();
     StartFlag = 0;
  }
}