I have a question about how to control time with the millis() function.

Projects Programming
1

Hello, everyone!

I'm writing code using the millis() function. I think the code is twisted because I'm not good at coding yet and I don't understand millis(). The code below provides an inclination through the 9-axis sensor and outputs different strings and LEDs depending on the left and right slopes.

What I want to do is, for example, tilt to the left, the functions below are implemented.

  1. Left LED illuminated for 1 second (if tilted to the left continuously, it remains on until switching to another direction).)

  2. Switching to the right before 1 second (not yet before LED goes off) turns the left LED off immediately and performs the right LED action.

+3. LED Immediate Switching only applies when tilting left or right. For example, if you tilt to the left and then place it in a flat state, the left LED turns on and then turns off after a second.

It's kind of like this, but I couldn't express it properly with code...
If I upload this code, you will only repeat the on/off toggle when it is within the specified value range.

//Based on the x-axis slope.
if(val_x < -30 && State == 0) //  right on
    {
      State = 1;
      unsigned long previousMillis = millis();
      Serial.println("갸LED ON");
      digitalWrite(right_led, HIGH);
      digitalWrite(left_led, LOW);
    }
    else if(val_x > 30 && State == 0) // left on
    {
      State = 1;
      unsigned long previousMillis = millis();
      Serial.println("왼쪽 LED ON");
      digitalWrite(left_led, HIGH);
      digitalWrite(right_led, LOW);
    }
    else
    {
      State = 0;
    }

    if( millis() >= previousMillis + 1000 && State == 0)//OFF
    {
      digitalWrite(left_led, LOW);
      digitalWrite(right_led, LOW);
      Serial.println("LED OFF");
    }

I would really appreciate it if you could tell me about my problem!
Thank you.

2

A millis() timing check should never be embedded in a conditional statement. If the conditional statement remains false for longer than the timing interval, the timing update will be missed.

3

Some pseudo code...

Now = millis()

If left sensor detected
  If Left == LOW
    LeftStart = Now
  Left = HIGH
Else If Now - LeftStart >= 1000
  Left = LOW

If right sensor detected
  If Right == LOW
    RightStart = Now
  Right = HIGH 
Else If Now - RightStart >= 1000
  Right = LOW

digitaWrite(leftLed, Left)
digitalWrite(rightLed, Right)
4

Please pay attention to the following:

  • the previousMillis variable MUST be a global variable.
  • checking time should NOT be inside any conditional block. make sure that is always check in the loop regardless any condition.

You can refer to how to use millis() function

5

Thank you all for your help! I'll refer to it and revise it.

6

I have a question about how to control time

You are going to be disappointed. Nobody has the power to control time :slight_smile:

The demo Several Things at a Time illustrates the use of millis() to manage timing without blocking. It may help with understanding the technique.

Have a look at Using millis() for timing. A beginners guide if you need more explanation.

...R

7

IoT_hobbyist:
Please pay attention to the following:

  • the previousMillis variable MUST be a global variable.

...or it could be a static variable.

8

This topic has been merged into I'm trying to control LED blinking within the range of the sensor values..