Change state of pin depending on PWM value of different pin

Using Arduino Programming Questions
1

Hi everyone,

Any help is appreciated. I would like to change the value of a pin from high to low based on the output value on another pin without having to physically measure it using the analog pins.

For example:
I am using the analogWrite() command to send a PWM signal to pin 5 on my Uno. I would like Pin 6 to go high if pin 5 is sending >=150, and Low if it is <150.

I managed to get this working by connecting pin 5 to A0 and using the analogRead() command. But I would rather use only code if possible, not additional wiring.

Any ideas?

Thanks!

2

mgale31:
Any ideas?

Thanks!

analog read wont work as you expect on a pin outputting PWM.

Just write to the digital pin contingent on what value you pass to the analog pin...

var myInput = getSomeValue();
analogWrite(somePin, myInput);
myInput >= 150? digitalWrite(someOtherPin, HIGH) : digitalWrite(someOtherPin, LOW);
3

Thanks @BulldogLowell!

I can't seem to get it to work. Do you mind having a look at my code? The If statement isn't working. No matter what I set rightGreen to, rightBlack will not change state.

 int rightGreen = 5;
 int rightBlack = 7;
 
 const int upperThreshold = 100; //Threshold values for the black wire logic
 const int lowerThreshold = 50;
 
 
 void setup() {
    pinMode(rightBlack, OUTPUT);
    pinMode(rightGreen, OUTPUT);
}

void loop() {


analogWrite(rightGreen, 90);


//check condition of right green wire
  if (rightGreen > upperThreshold || rightGreen < lowerThreshold) 
  {
    digitalWrite(rightBlack, HIGH);
  } 
  else 
  {
    digitalWrite(rightBlack, LOW);
  }
}
4

rightGreen is the output PIN not the value to be tested...

you set it here:

analogWrite(rightGreen, 90);

why are you then immediately comparing it here:

  if (rightGreen > upperThreshold || rightGreen < lowerThreshold) // you KNOW it is 90!!

??

5

rightGreen is 5...

So your test comes out to:

if (5> 100 || 5 < 50)

5 is always less than 50, so the if statement is always true. You probably wanted to test the duty cycle you set the pin to, not the number of the pin.

6

You want:

 int rightGreen = 5;
 int rightBlack = 7;
 
 const int upperThreshold = 100; //Threshold values for the black wire logic
 const int lowerThreshold = 50;
 
 
 void setup() {
    pinMode(rightBlack, OUTPUT);
    pinMode(rightGreen, OUTPUT);
}

void loop() {


analogWrite(rightGreen, 90);


//check condition of right green wire
  if (90 > upperThreshold || 90 < lowerThreshold) 
  {
    digitalWrite(rightBlack, HIGH);
  } 
  else 
  {
    digitalWrite(rightBlack, LOW);
  }
}

[/quote]

7

Thanks guys!
I should have been more clear. the code I attached above is just testing a theory. Eventually I will have a potentiometer connected to the circuit that will be changing the value of "rightGreen", and I want rightBlack to respond accordingly. I was just using this code to manually change the value rightGreen to see if rightBlack responded appropriately.

You guys got me sorted out.

I just created another variable to run the if statement. This does exactly what I want. Hopefully this is correct practice?

 int rightGreen = 5;
 int rightBlack = 7;
 int rightGreenVal = 0;
 
 const int upperThreshold = 100; //Threshold values for the black wire logic
 const int lowerThreshold = 50;
 
 
 void setup() {
    pinMode(rightBlack, OUTPUT);
    pinMode(rightGreen, OUTPUT);
    rightGreenVal = 84;
}

void loop() {


analogWrite(rightGreen, rightGreenVal);


//check condition of right green wire
  if (rightGreenVal > upperThreshold || rightGreenVal < lowerThreshold) 
  {
    digitalWrite(rightBlack, HIGH);
  } 
  else 
  {
    digitalWrite(rightBlack, LOW);
  }

}

Thanks again for the guidance guys. Much appreciated

8

I don't understand why you have thresholds

if (rightGreenVal > upperThreshold || rightGreenVal < lowerThreshold)

a PWM pin driven by analogWrite() will be either HIGH or LOW with nothing in between.

If you want a second external item to see the same value as is on the PWM pin my first question is why not just connect the two things to the PWM pin?

...R

9