How to check if a condition is true only for the first time

Projects Programming
1

Hey
I want to save information when a condition is checked and found to be true but I only want to save the information the first time the condition happened.
In my case, I want to store the time when a motor (with encoder) reaches the target position for the first time. If it reaches, then I want to save the reaching time, and if it reaches again I want my saved time to remain the same as the first time the motor reaches the target position.
I tried this code:

if (pos == target); {
      targetAchive = 1;
      targetTime = millis();
      targetAchive = 0;
    }

but if the motor overshoots the target position and returns for the second time to the target position - the "targetTime" get changed.
Thanks

2 
bool firstTime = true;
...
if (pos == target and firstTime == true) {
      targetAchive = 1;
      targetTime = millis();
      targetAchive = 0;
      firstTime = false;
    }

Your code has a bug, there should be no semicolon after the if statement, just a brace {.

Also you have contradictory code, targetAchive always gets set to 0 after it is set to 1. So the first line does nothing. Not sure what you are trying to do.

3

Hi,

I think this will do what you require:

  if (pos == target && targetAchive == 0) {
      targetTime = millis();
      targetAchive = 1;
    }
4

Welcome to the forum.

Study state machines. The Boolean provided is the most basic of these. The principle is important.

5

this code never will do what you expected because the semicolon after the condition.

6

good spotting.

7

but bit late... may be :slight_smile:

8

Thank you
I tried your solution and its worked.

9

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.