Detecting a 2.8ms pulse using a Arduino Uno

Question

I am working on a project for knowing the position of a DC motor which has a hall sensor built into it. I am a newbie into programming using the Arduino Uno R3. After some forum search and self checks, I cannot pass this hurdle. I hope I can frame the questions properly here.

My Problem: The DC motor hall sensor sends out 2 high pulse of 11.3V - 13V with a duration of 2.8ms for each revolution. My Arduino interrupt pin doesn't read the high pulse as it gives me "0" count after motor spin (I run 50 loops and results remain the same).

On my breadboard, I use a voltage divider to reduce hall-effect ouput from max 13V to 5V so that the Arduino pin 2 can read rising voltage when it jumps to 5V (low should be 2.5V).

Couple of things I noted during the motor spin -

a) The millis() function returns 79-81ms per sketch run

b) The same hall sensor output if connected to analog pin reads 580,590,590,1001, 1012, 580, 580.. etc. I cannot gauge position of the motor by using these values as they are inconsistent on the way up Vs. way down.

I have attached analog readings while going up and down in snap shot below: 2 questions I have:

1. Why is the pin 2 not detecting a high pulse? will it not be able to read 2.8ms durations because of motor speed (9.5 rev/s or 570rpm)?
2. Is it possible to gauge anything from Analog read function? Am I missing something?

Thanks in advance for all responses.. Any questions regarding the circuit, I will be more than happy to post them.

Answer 1

First, better to see whole source and schematics.

"Why is the pin 2 not detecting"

Check: 1. Hall sensor connected to Pin 2

2. pulses variable declared as volatile.

3. Check if internal pull up resistor setup consistent with hall sensor connection.

4. Check that Hall sensor's lowest signal voltage is below 0.3 VCC (you said 5V, so it should drop below 1.5V), BTW 580 - the lowest analog value you showed means 2.83V

5. Check you are not using nointerrupt();

"Is it possible to gauge anything from Analog read function? Am "

Yes. Analog read takes about 0.1 ms in default setup, so should make at least 1000 reads per second to catch peak.

So, Easiest way is to choose some value like 600, when analog read is above mark it as Rising when it drops below mark is Falling. More complicated ways will include some training and hysteresis to improve detection.

Also I suggest to use voltage limiter instead of voltage divider. This gives better detection.

Answer 2

All,

Here is the code:

int flag = 1;
int speedo = 255;
          int counter =0; //counts the number of revolutions
          int timeu=0;
          int timed=0;
          int Voltmeasure=0;
          int times=0;
          volatile unsigned int pulses=0; //pulse counter
          bool upcount=false;
          bool downcount=false;
          unsigned int timeold=0;
          int difference=0;

          void count()
          {
            if(upcount==true)
              pulses++;
              else if (downcount==true)
               pulses--;
          }

          void setup() 
          {
            // initialize serial communication:
            Serial.begin(9600);
            pinMode(11,OUTPUT);
            pinMode(12,OUTPUT);
            pinMode(13,OUTPUT);
            pinMode(2, INPUT);
            pinMode(3, INPUT);
            attachInterrupt(digitalPinToInterrupt(2),count, RISING);
          }
          void stopmotor()
          {
            digitalWrite(12,HIGH);
            digitalWrite(13,HIGH);
          }
          void motorCCW()
          {
            analogWrite(11,speedo);
            digitalWrite(12,HIGH);
            digitalWrite(13,LOW); 
          }
          void motorCW()
          {
            analogWrite(11,speedo); 
            digitalWrite(12,LOW);
            digitalWrite(13,HIGH);
          }

          void loop() 
          {  
              if(flag==1)
              {
                delay(2000); //wait for 2 seconds to start motor
                flag=2;
              }

            //first run motor moves down
                if (counter<16 && flag==2)
                {
                  motorCW(); //moving up

                  //Reading Hall-sensor pulses- using analog signal
                  Voltmeasure = analogRead(A3);
                  Serial.print("CW Voltmeasure = ");
                  Serial.print(Voltmeasure);
                  Serial.println();

                  //Reading Hall-sensor pulses - using interuppt signal
                  upcount=true;

                  //counting the number of high pulse
                  if (Voltmeasure>700 && times==0)
                  {
                    counter++; times=1;
                  }
                  else if (Voltmeasure<610)
                    times=0;  

                  //timer for number of loops
                  timeu++;
                  Voltmeasure=0;

                  if (timeu==70||counter==16) //move by 70 cycles or until counter is 16
                  {
                    stopmotor();
                    upcount=false;
                    timeu=0;
                    times=0;
                    Serial.print("High-point is reached - Travel complete");
                    Serial.println();
                    delay(2000); //delay by 2 seconds
                    flag=3;
                  }
                }

                if (counter>0 && flag==3)
                {
                  delay(2000); //pause before next run
                  motorCCW();

                  //Reading Hall-sensor pulses - using analog signal
                  Voltmeasure = analogRead(A3);
                  Serial.print("CCW Voltmeasure = ");
                  Serial.print(Voltmeasure);
                  Serial.println();

                  //Reading Hall-sensor pulses - using interuppt signal
                  downcount=true; 

                 //counting the number of high pulse
                  if (Voltmeasure>700)
                  {
                    counter--; times=1;
                  }
                  else if (Voltmeasure<610)
                    times=0;   
                  timed++;
                  Voltmeasure=0;

                  if (timed==70||counter==0) //move by 70 cycles or until counter is 0
                  {
                    stopmotor();
                    downcount=false;
                    timed=0;
                    times=0;
                    Serial.print("Lowest point is reached - Travel complete");
                    Serial.println();
                    flag=3;//stop motor 
                  }
                 }

          //  difference=millis()-timeold;
          //  timeold = millis();
          //  
          //  //Printing information after line complete
          //  Serial.print("time for one sketch = ");
          //  Serial.print(difference);
          //  Serial.println();

            Serial.print("Counter = ");
            Serial.print(counter);
            Serial.println();

            Serial.print("pulses = ");
            Serial.print(pulses);
            Serial.println();


          }

General block diagram

Motor with Hall sensor, Ve is 13V, Ue is 13.5V:

I print the counter (Analog pin) and pulses (interrupt pin) with running this program code.

The Analog pin reads:

CW Voltmeasure = 574

CW Voltmeasure = 588

CW Voltmeasure = 1000

CW Voltmeasure = 999

CW Voltmeasure = 998

CW Voltmeasure = 1002

CW Voltmeasure = 1002

CW Voltmeasure = 589

CW Voltmeasure = 588

CW Voltmeasure = 590

CW Voltmeasure = 588

CW Voltmeasure = 1000......by this time motor spins 6.5 rev (based on time elapsed) but counter is only @ 3 (3 highs)

Pulses read 0.......

This is where i am at. Not able to understand Analog readings dont match the number of revs with the highs & why interupt pin reads 0......

Answer 3

I tried modifying the voltages to interrupt pins

Now interrupt pin voltages read: High:1.456V Low: 1.07V

Note: The arduino is running at 12V external source.

My "pulses" counter still reads 0 for interrupts. Any idea why?

Answer 4

All,

My Arduino is not reading interrupts across the interrupt pin:

I am getting a high of 1.456V and a low 1.07V through the interrupt pin 2... But the pulses counter still remain 0....

Any idea why?

  volatile unsigned int pulses=0; //pulse counter
  volatile int8_t steps=0;
  int timeu=0;
  int flag=2;

  void count()
  {
    pulses++;
  }

  void setup() 
  {
    // initialize serial communication:
    Serial.begin(9600);
    pinMode(11,OUTPUT);
    pinMode(12,OUTPUT);
    pinMode(13,OUTPUT);
    pinMode(2,INPUT_PULLUP);
    attachInterrupt(digitalPinToInterrupt(2),count,RISING);

  }

  void stopmotor()
  {
    digitalWrite(12,LOW);
    digitalWrite(13,LOW);
    steps=0;
  }
  void motorCCW()
  {
    analogWrite(11,255);
    digitalWrite(12,HIGH);
    digitalWrite(13,LOW); 
    steps=-1;
  }
  void motorCW()
  {
    analogWrite(11,255); 
    digitalWrite(12,LOW);
    digitalWrite(13,HIGH);
    steps=1;
  }

  void loop() 
  {  

    if (timeu<=1000)//First time - Going up
    { 
        sei();
        motorCW(); //moving up
        flag=8;
        timeu++;
      } 
    else if (timeu==1000)
      {
          flag=10;
          stopmotor();
          cli();
          //Serial.print("Completed time cycle of 50");

      }



  if (flag==10)
  {
    Serial.print("pulses = ");
    Serial.print(pulses);
    Serial.println();


  }



  }

Answer 5

All,

I didnt need the voltage comparator in the end, the code was running slower and wasnt picking up all the hall sensor signals that the motor was giving due to loop time. i changed the ifs to else ifs and then i was able to get a faster loop time.

Thanks all for the help.

The device is working as intended..