pin LOW when a condition is reached after setting PWM on that PIN

Projects Programming
1

Hello to everybody,

I have settled the PWM on the pin 10 of my Arduino Mega to 1 kHz using Timer 2. After certain time, when a condition is reached (counter==1000), I want to output low signal (0V) from that pin. The problem is that my PIN will not go down even if i state digitalWrite(10, LOW);

That's my simple code:

const byte PULSES = 10; // Timer 2 "A" output: OC2A --> 1 kHz
const byte home_switch=9; // Pin 9 connected to Home Switch (Photointerrupter)
#define encoderPinA 2
#define encoderPinB 3
volatile int counter =0;
unsigned long time;
int incomingByte = 0; // for incoming serial data

void setup() {
pinMode (PULSES, OUTPUT);
pinMode(home_switch, INPUT_PULLUP);
pinMode(encoderPinA, INPUT);
pinMode(encoderPinB, INPUT);
attachInterrupt(digitalPinToInterrupt(encoderPinA), isr,RISING);
Serial.begin(9600);

delay(5); //

// set up Timer 2
int myEraserPulses = 7; // this is 111 in binary and is used as an eraser
TCCR2B &= ~myEraserPulses; // this operation (AND plus NOT), set the three bits in TCCR2B to 0

TCCR2A = _BV(COM2A0) | _BV(WGM21) | _BV(WGM20); // fast PWM
TCCR2B = _BV(WGM22) | _BV(CS21) | _BV(CS22); // 16MHz/256=62.5kHz
OCR2A = 30; // 62.5kHz/1kHz=62.5 (50% duty--> 30)

} // end of setup

void loop() {

if(counter==1000)
digitalWrite(10, LOW); //output 0 V so the motor will stop
else
digitalWrite(10, HIGH); // continue to output PWM at 1kHz

if (Serial.available() >= 0) { // read the incoming byte:
incomingByte = Serial.read();

Serial.print(counter);
Serial.print("\t");

Serial.print("Time: ");
time = millis();
Serial.println(time); //prints time since program started

if (incomingByte=='0') { //pressing 0 into the serial monitor to stop the program
while(1) { }
}
}
}
//Interrupts
void isr(){

int channel_A = digitalRead(encoderPinA);
int channel_B = digitalRead(encoderPinB);

if(channel_A == channel_B){
counter++;
}
else{
counter--;
}
}

Thanks for your help.

2

I think you will have to turn off the PWM output before you try to set the output. I think setting TCCR2A to 0 will stop the PWM output (by setting COM2A0 and COM2A1 to 0).

3

Thanks for the prompt answer. Do you mean something like that?

void setup() {
pinMode (PULSES, OUTPUT);
pinMode(home_switch, INPUT_PULLUP);
pinMode(encoderPinA, INPUT);
pinMode(encoderPinB, INPUT);
attachInterrupt(digitalPinToInterrupt(encoderPinA), isr,RISING);
Serial.begin(9600);

delay(5); //

// set up Timer 2
int myEraserPulses = 7; // this is 111 in binary and is used as an eraser
TCCR2B &= ~myEraserPulses; // this operation (AND plus NOT), set the three bits in TCCR2B to 0

TCCR2A = _BV(COM2A0) | _BV(WGM21) | _BV(WGM20); // fast PWM
TCCR2B = _BV(WGM22) | _BV(CS21) | _BV(CS22); // 16MHz/256=62.5kHz
OCR2A = 30; // 62.5kHz/1kHz=62.5 (50% duty--> 30)

} // end of setup

void loop() {

if (counter==-1000)
TCCR2A &= ~(_BV(COM2A0));
else
TCCR2A = _BV(COM2A0) | _BV(WGM21) | _BV(WGM20);
}

I tried but it doesn't work.

4

D10S:
Thanks for the prompt answer. Do you mean something like that?

void loop() {

if (counter==-1000)
   TCCR2A &= ~(_BV(COM2A0));
 else
   TCCR2A = _BV(COM2A0) | _BV(WGM21) | _BV(WGM20);
}



I tried but it doesn't work.

More like:

void loop()
{
  if (counter == -1000)
  {
    Serial.println(F("PWM OUTPUT OFF"));
    TCCR2A &= ~(_BV(COM2A0));  // Turn off PWM output
    digitalWrite(PULSES, LOW); //output 0 V so the motor will stop
  }
  else
  {
    TCCR2A |= _BV(COM2A0);  // Make sure PWM output is on
  }
5

It actually doesn't work. In the serial port it will show "PWM OUTPUT OFF" but the the motor will not stop since the pwm is still at 1 Khz. It isn't dropping to 0V.

See "fail" attached.

This is probably because count is a VOLATILE INT?

I still think the problem is that the PWM is not going out because it is actually able to understand when count is 1000

fail.PNG
fail.PNG896×546 28.6 KB

6

Please post the entire revised code. Also please bracket it with code tags as you can see done in reply#3. There are instructions on how to do that in the sticky threads at the top of the forum.

Error messages should be posted that way, too.

7

That's the revised code. Apologize for that

const byte PULSES = 10;  // Timer 2 "A" output: OC2A --> 1 kHz
const byte home_switch=9; // Pin 9 connected to Home Switch (Photointerrupter)


#define encoderPinA 2 // encoder channel A
#define encoderPinB 3 // encoder channel B
volatile int counter =0; // pulses counter of the encoder
unsigned long time;
int incomingByte = 0;   // for incoming serial data

void setup() {
pinMode (PULSES, OUTPUT); // set the pulses pin as output
pinMode(home_switch, INPUT_PULLUP); // set the photointerrupter as an input
pinMode(encoderPinA, INPUT); // set the encoder as an input
pinMode(encoderPinB, INPUT); // set the encoder as an input
attachInterrupt(digitalPinToInterrupt(encoderPinA), isr,RISING); //pulses counting
Serial.begin(9600);

 delay(5);  //
 
  // set up Timer 2
int myEraserPulses = 7;             // this is 111 in binary and is used as an eraser
TCCR2B &= ~myEraserPulses;   // this operation (AND plus NOT),  set the three bits in TCCR2B to 0

TCCR2A = _BV(COM2A0) | _BV(WGM21) | _BV(WGM20); // fast PWM
TCCR2B = _BV(WGM22) | _BV(CS21) | _BV(CS22); // 16MHz/256=62.5kHz
OCR2A = 30; // 62.5kHz/1kHz=62.5 (50% duty--> 30)       

}  // end of setup

void loop()
{
  if (counter == -1000)
  {
    Serial.println(F("PWM OUTPUT OFF"));
    TCCR2A &= ~(_BV(COM2A0));  // Turn off PWM output
    digitalWrite(PULSES, LOW); //output 0 V so the motor will stop
  }
  else
  {
    TCCR2A |= _BV(COM2A0);  // Make sure PWM output is on
  }

if (Serial.available() >= 0) {  // read the incoming byte:
  incomingByte = Serial.read();
 
  Serial.print(counter);
  Serial.print("\t");
 
  Serial.print("Time: ");
  time = millis();
  Serial.println(time); //prints time since program started
 
if (incomingByte=='0') { //pressing 0 into the serial monitor to stop the program
   while(1) { }
}
}
}
//Interrupts
void isr(){

    int channel_A = digitalRead(encoderPinA);
    int channel_B = digitalRead(encoderPinB);
 
   if(channel_A == channel_B){
    counter++;
   }
   else{
    counter--;
   }       
}

Even if it is able to understand when count reaches -1000, the signal on the PULSE input will not drop to 0. Therefore the motor is not stopping

8

I actually SOLVED it! The problem was that the encoder readings might not be 1000 but 1002 or 996, so i just picked a range of values:

void loop()
{
  if (counter > -1005 && counter < -995)
  {
    Serial.println(F("PWM OUTPUT OFF"));
    TCCR2A &= ~(_BV(COM2A0));  // Turn off PWM output
    digitalWrite(PULSES, LOW); //output 0 V so the motor will stop
  }
  else
  {
    TCCR2A |= _BV(COM2A0);  // Make sure PWM output is on
  }

Thanks guys!