How to make a loop happen for a limited amount of time

Projects Programming
1

I am currently dealing with stepper motors and am trying to make a basic script that allow me to type how long I want to the motors to run for into the serial monitor however at the moment they just keep moving not matter what number I place in. I still struggle with the for command (I am kinda new) and was wondering if I could get some help

#include <Adafruit_PWMServoDriver.h>
int time;

#include <Wire.h>
#include <Adafruit_MotorShield.h>
Adafruit_MotorShield AFMS = Adafruit_MotorShield();
String msg="What length?";
Adafruit_StepperMotor *myMotor = AFMS.getStepper(200, 1);
Adafruit_StepperMotor *myMotor2 = AFMS.getStepper(200, 2);
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
myMotor->setSpeed(10); // 10 rpm
myMotor2->setSpeed(10); // 10 rpm
AFMS.begin();
time=0;

Serial.println(msg);

}

void loop() {
  while (Serial.available() == 0); //waiting for input    
int time = Serial.parseInt(); //read as integer
  for (int i = 0 ; i < time ;){
    myMotor->step(1, BACKWARD, SINGLE);
myMotor2->step(1, BACKWARD, SINGLE);
     Serial.print('.');
  }


  // put your main code here, to run repeatedly:

}
2

The above is an infinite loop, if time is greater than zero, because i is initialized to zero then never changed from 0. Perhaps you mean something like this:

  for (int i = 0 ; i < time ; i++){

If you are confused about a C/C++ language element, consult the incredibly handy C/C++ language reference pages.

1 Like
3

I am still a bit confused on how for works. I made a test code here And whenever I use it I expected the serial monitor to print ".' repeatedly for 10 seconds however it only prints it once, do you know what I am doing wrong?

String msg="Go?";
String go;
int i;
void setup() {
Serial.begin(9600);
}

void loop() {
Serial.println(msg);
while(Serial.available()==0){
}
go=Serial.readString();
go.trim();
if(go=="yes"){
  for(int i = 0 ; i < 10000 ; i++);
  Serial.println(".");
} else {
  i=0;
}
}
4

The program is doing exactly what you wrote it to do.

The ";" after the for statement is the entirety of the loop action, which is "do nothing".

You can't just randomly throw in bits of language syntax and expect things to work.

One correct approach to printing 10000 periods would be this:

  for(int i = 0 ; i < 10000 ; i++) {
  Serial.println(".");
}
5

look this over

unsigned long msecPeriod;
unsigned long msecLst;

bool run;

void loop ()
{
    // timer
    unsigned long msec = millis ();
    if (msecPeriod && msec - msecLst >= msecPeriod)  {
        msecPeriod = 0;
        run        = false;
        Serial.println ("done");
    }

    // run when enabled
    if (run)  {
        Serial.println (msec);
        delay (500);
    }

    // enable run when there is input
    if (Serial.available ())  { // wait for something to read
        Serial.read ();         // does it matter what is read?
        run = true;
        msecPeriod = 5000;      // 5 sec
        msecLst    = msec;
    }
}

void setup () {
    Serial.begin (9600);
    Serial.println ("ready");
}
6

Here, 1 dot / sec, for 10 secs. (10 dots) --

const unsigned long Hz1 = 1000;
const unsigned long theEnd = 10000;
unsigned long markTime;
unsigned long tentimes;

void setup() {
  Serial.begin(19200);
  delay(2000);
  Serial.print("ready\r\n\r\n");
  markTime = millis();
  tentimes = millis();
}

void loop() 
{
  if( millis() - tentimes <= theEnd )
  {
    if (millis() - markTime >= Hz1)
    {
      Serial.print(".");
      markTime = millis();
    }
  }
}
7

No, if that code didn't have the offending semicolon it would print '.' to the screen 10,000 times. It would happen really really fast though. It would take a LOT less than 10 seconds.

8

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