Cannot get interupts to work consistently

[pruett99]

I have a pulse meter on a fuel pump that sends out a pulse for every 0.1 gallons. That pulse meter triggers a relay to turn on and off. The switched side of the relay switches a 5v signal from the Arduino and the other side goes to pin 2 on the Arduino. I also have a 10k resistor being used as a pullup resistor.

I am using interrupts to keep track of gallons passed through the meter. The problem I have is that the interrupts are getting triggered inconsistently. Sometimes it double triggers, triple, etc. Sometimes it doesn't even fire at all.

The signal triggering the relay is consistent. I have even tried a second arduino to trigger the relay on consistent intervals and I come across the same problem. I have many hours into trying to solve this problem. Any help would be appreciated. I have attached my code below.

int counterPin = 2;
volatile float count = 0;
void setup() {
  Serial.begin(9600);
  pinMode(counterPin, INPUT);
  digitalWrite(counterPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(counterPin), countFuel, FALLING);
}

void loop() {
  Serial.println(count);
}

void countFuel(){
  count = count + 0.1;
}

[van_der_decken]

Where is the signal being input to pin 2 coming from? Is it a mechanical switch or a relay contact? If so, you need to debounce it.

[Paul_KD7HB]

@pruett99

The switched side of the relay switches a 5v signal from the Arduino and the other side goes to pin 2 on the Arduino. I also have a 10k resistor being used as a pullup resistor.

Why? If you are using a pullup resistor, all the relay needs to do is ground the wire from pin 2. The way you have the circuit, pin 2 is switched from 5 volts on the resistor to 5 volts on the Arduino.

[camsysca]

From your description, it's contact bounce. An interrupt can trigger many times in a millisecond, so if the contact makes 10 bounces before settling(usually within a few ms), you'll have many increments to your flow.

You need to debounce the signal, and debouncing(filtering) and interrupts don't go well together. An electronic debounce with a single output transition would do you better if you're sticking with the interrupt approach.

However, how fast is your pump pumping? My guess is 60 gpm would be extreme; at that rate, you'd be pulsing 10 times per second. No need for an interrupt here, it's just a simple contact closure and debounce-in-software.

[gfvalvo]

@pruett99

volatile float count = 0;

First, there's no reason to use a 'float' to count discrete events. Use an unsigned integer type, it will be more efficient, especially on processors that don't have hardware support for floating point calculations.

@pruett99

Serial.println(count)

What type of Arduino board? Access to a 4-byte float will be non-atomic on an 8-bit AVR processor. It needs to be protected with a Critical Section.

EDIT:
@alto777 just mentioned that below while I was typing.

[alto777]

@pruett99

volatile float count = 0;

When you use this multibyte variable outside of the interrupt service routine, you have to do it with interrupts turned off.

Ppl usually grab a copy to work with, viz:

  noInterrupts();
  float myCounter = counter;
  interrupts();

then use myCounter everywhere below.

It may not be your only problem.

HTH

a7

[camsysca]

never mind.

[johnerrington]

@pruett99

That pulse meter triggers a relay to turn on and off.

Can you provide a schematic and links to those components please ?
"relay" covers a wide range of components!

How to make a schematic you can post.

When you submit a question on the forum you will usually need to add a schematic (circuit diagram). The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy. Having created the image all you need to do is : Save the image somewhere convenient - maybe your desktop Start your post, and place the cursor (insertion point) where you want the image to be shown; [upload image to forum] 3: click th…

The code is so siomple it would appear to be a hardware issue.