Interrupts for analog pulse width input and alternating LEDs

Other Hardware LEDs and Multiplexing
1

Hello there,

I am new to Arduino and find it very hard to diagnose the issue I'm having with a simple application of interrupts.

The background of the project is:
I am looking to alternate the switching on and off of two LEDs, so when one turns on the other turns off, every time an input analog pulse width signal is high. I am currently generating an analog signal with an external device and software (Waveforms and Discovery kit if that information is needed) and connecting it to the interrupt pin (pin 2) to trigger the interrupt. However, that was not working and the LEDS were not flickering in sync with the period of the pulse width being generated. Therefore, I switched the input source to be the 5V source from the Arduino with a button to see if that would work better.

when the button is pressed and the 5V is able to be read by the pin, the LEDs will switch. Printing to the serial port, there is "1" being printed, but, when the button isn't pressed, there's a bunch of sporatic 1 and 0 being inputted and then printed to the serial monitor and the LEDs are flickering
like crazy even though there is not supposed to be any voltage going to the pin.

So, basically:

How can I use interrupts with an analog input pulse width signal of 5V to identify and change LEDs alternatingly?

I will note also that LEDs are connected in series with 1k resistors, to pins 7 and 8, they were originally connected to pins 5 and 6 PWM if that makes any difference

my current code:

const byte redLEDPin = 7; // set red led output to 5 (PWM pin, not sure if that is goingto beb necessary since its a logical output 
const byte greenLEDPin = 8; // set green led to 6 (PWM pin) 


volatile bool redLEDState; // initial state of led, let us know if the circuit is on 
volatile bool greenLEDState;





void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
  pinMode(redLEDPin, OUTPUT);
  pinMode(greenLEDPin, OUTPUT);
  pinMode(2, INPUT);


  redLEDState = true;
  greenLEDState = false;
  digitalWrite(redLEDPin, redLEDState);
  digitalWrite(greenLEDPin, greenLEDState);
  
  attachInterrupt(0, PulseISR, FALLING);
}

void loop() {
Serial.print(digitalRead(2));
}

void PulseISR() {
    if (redLEDState) {
    redLEDState = false;
    greenLEDState = true;
    digitalWrite(redLEDPin, redLEDState);
    digitalWrite(greenLEDPin, greenLEDState);
  }
  else if (greenLEDPin) {
    redLEDState = true;
    greenLEDState = false;
    digitalWrite(redLEDPin, redLEDState);
    digitalWrite(greenLEDPin, greenLEDState);
  }
  else {
    Serial.print("error");
  }
}
2

How is pin 2 wired ?

Is it always in a known state or does it sometime float at an unknown voltage ?

3

Just a hint you are actually seeing what the button does. They are not simply on or off, they bounce and generate several pulses when cycled. Some switches are better than other and they will change with time. You will need to do what is called debouncing. Rather than giving you code I recommend that you do some research on it. Also debouncing can be done in both the digital and analog domain.

Doing your processing in the ISR (Interrupt Service Routine) is not a good practice. The best is to set a flag and do the processing externally in the loop.

4

Try INPUT_PULLUP as opposed to just INPUT. Try the configuration of S2 as in the drawing below:

SwitchesAndLEDs
SwitchesAndLEDs1224×1108 280 KB

5

Doing anything in the ISR is not necessarily a good practice.

Particularly using an interrupt to monitor a pushbutton or mechanical contact. I cannot really figure out from the description so far whether this is what is proposed here. :roll_eyes:

6

When an input is not connected to anything we say it is floating. That means it picks up interference and can read anything.
Here is a full explanation of what is happening
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

You should not use a serial print inside an ISR.

7

That sounds like you are saying you want one led to be on when the input is high and the other led to be on when the input is low. You don't need an Arduino for that.

What is an "analog pulse width signal"? It sounds like a contradiction. A pulsed signal is digital. Do you mean that the duty cycle of the digital PWM signal represents an analog value?

8

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