Need help in writing a function

Question

I am reading an accelerometer using arduino. Basically i receive positive values and I need to get only first row of negative values. E.g. I receive values > -0.5 , then I start to have values < -0.5 (which i put them into an array , and then in case I get again values greater than -0.5 I want to stop it.

Also if in 30 seconds it should stop anyway. This is what I did till now but is not working like expected

void reading_mpu_brake(){
          unsigned long StartTime = millis();
     
      float acc[500];
      int read_time[500];
    
      byte arrayIndex = 0;
    
    while(1){
      unsigned long CurrentTime = millis();
      if (CurrentTime - StartTime < interval) {
        mpu.update();
        if (mpu.getAccX() < -0.05){
          total_acc = sqrt((pow((mpu.getAccX() - offsetx), 2) + pow((mpu.getAccY() - offsety), 2) + pow((mpu.getAccZ() - offsetz), 2) ));
          
          acc[arrayIndex] = total_acc; 
          read_time[arrayIndex] = millis();
          
          Serial.print(acc[arrayIndex]);
          Serial.print(" | ");
          Serial.print(mpu.getAccX());
          Serial.print(" | ");
          Serial.println(read_time[arrayIndex]);
          Serial.println(arrayIndex);
           arrayIndex++;
        }
      }  
      else if (CurrentTime - StartTime > interval)
      {
        Serial.println("Over time");
        break;
      
      
      }
    
    }

Now is working and get values less than -0.5 but if after several good values if I get positive values and then again negative it will put in array also the last one which I don t.

So basically I need to stop it after first bunch of good values...

Any help appreciated

Thank you!

L.E. Seems I miss a good explanation so I will try again.

1 - I call the function and it start monitoring values for 30 seconds.

Case 1 : I receive 0.6 , 0.7 , 0.4 , 0.2 , -0.2 , -0.6 , -0.7 , -0.8 , -0.4 , 0.3 , 0.5 ...etc

In this case I get into acc array values : -0.6 , -0.7 , -0.8 then after 30 sec gone the function exit

That is OK partially .

Case 2 : I receive 0.6 , 0.7 , 0.4 , 0.2 , -0.2 , -0.6 , -0.7 , -0.8 , -0.4 , 0.3 , 0.5 , -0.6 , -0.7 , 0.6...etc

In this case I get into array values -0.6 , -0.7 , -0.8 and if the 30 secs are not gone I also get -0.6 , -0.7 .

What I want is function to exit after get first bunch of good values (-0.6 , -0.7 , -0.8) .

Hope now is more clear

I edited and added more explanations. By "row of negative values" mean first bunch of values that met criteria to be < -0.5 — lucian_v
– lucian_v, Commented Sep 8, 2021 at 8:10
it is clear what you are trying to do ... it is unknown what happens when you run the code ... not working as expected does not mean anything specific — jsotola
– jsotola, Commented Sep 8, 2021 at 15:21

Nick Gammon · Accepted Answer · 2021-09-08 11:36:23Z

5

float acc[500];
int read_time[500];

Right, so a float is 4 bytes on this platform, so that array takes 2000 bytes. And an int is 2 bytes, so that other array is another 1000 bytes.

The Uno has 2KB of RAM, so those two declarations alone take up more RAM than the device has.

I'm a little surprised it works at all, but certainly "not working as expected" is indeed an expected outcome here.

edited Sep 8, 2021 at 11:36

answered Sep 8, 2021 at 11:21

Nick Gammon♦

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