analogRead in "for loop" not giving same values as outside of it

Question

Arduino (https://www.amazon.de/gp/product/B01D0OI90U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1)

In this code I am sending a pulse to a motor driver (lines 8-11). The time between those pulses is determined by line 11 with the variable V. In order to make the motor move to a certain position I am looping the pulses L amount of times, and then (in lines 13-17) I am reversing the direction so it returns to origin. So L is the length the motor drives, while V is the speed at which it does that.

However, V (and soon L) is a value I read from a potentiometer (line 6) - which I should move into the loop so I get instantaneous changing of the speed. Instead of having to wait for it to complete the loop each time before it changes. But when I do that, it doesn't reach the same speed anymore. Instead of having 2.6us (us: microseconds) between pulses. it feels more like 200us - while if its outside the loop it can reach much higher speeds - but I dont know why!

Thanks in advance for all answers/time investments:

I tried moving the code block (the code in line 6) into the loop and it slowed the max speed tremendously.

I then moved the code block both to void setup, where it just didn't work at all and then before void setup - where it didn't adjust to the speed anymore and just ran at around 222us (us: microseconds).

Since it clearly is capable of reaching the speeds, I think it is somehow connected to some aspect of the code/language that I am unfamiliar with - and since I am a, noob that's basically all of it.

Answer 1

You are effectively blocking the analogRead every time because you are running the entire loop afterwards which also contains a bunch of delays.

Your code reads something like this

• decide how far to go (800 * 4) = 3600

• check how fast = V

• 3600 times do the following(

  • send a pulse
  • wait for 2.6us
  • send stop pulse
  • wait for V amount of time
  • wait 50us
  • change direction

  )end of 3600 times repeat

This means that on every move you will at least have 52.6 micros delay (as a minimum and depends on the V value).

Instead of doing the loop (inside loop()) every time you can simply keep the motor running and just change the direction when needed:

int L = 800 * 4; // put in the loop() is you will be changing this dynamically
int direction = 1; // 1 = forward , -1 = backward
int distance = 0;

void loop() {

    int V = map(analogRead(PotV),0,1023,V_max, V_min);
    
    distance = distance + direction; //increment or reduce the traveled distance 

    //decide on the change of direction 
    if(distance >= L){ //if we have traveled over the max distance L, reverse the direction
        direction = -1
        delayMicroseconds(50); //only delay once the motor is changing direction
        digitalWrite(dir,LOW); 
    }else if(distance <= 0){ //if we are back to start reverse direction to forward
        direction = 1
        delayMicroseconds(50); //only delay once the motor is changing direction
        digitalWrite(dir,HIGH); 
        
    }

    // pulse the motor 
    digitalWrite(pulse,HIGH);
    delayMicroseconds(2.6);
    digitalWrite(pulse,LOW);
    delayMicroseconds(V);
    

}

This will keep running the motor back and forward for the desired distance, if you want to only run it once (for example on a button press) then you can just include another variable that when true will enable the code and when the motor get's back to 0 position will reset itself to false