Interrupt is activated as soon as I insert a jumper wire into the port

Question

I have written a very simple code to test the interrupt functionality of my Arduino Uno expansion board:

const byte buttonPin3 = 3; 


void setup() {
  pinMode(buttonPin3, INPUT); 
  attachInterrupt(digitalPinToInterrupt(buttonPin3), trigger, CHANGE);

  Serial.begin(9600);
}

void loop() {
}



void trigger(){
  Serial.println("trigger");
}

However, the Serial.println("trigger"); is activated as soon as I insert a jumper wire into pins 2 or 3. It seems like I have broken the microcontroller. I would appreciate if you could help me know if there is something wrong with my code or I need to change the microcontroller? if I have to replace the MCU can I just use any identical AVR and just place it on the DIP IC socket adaptor?

P.S. Filip Franik asked me to draw the schematics:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

P.S. I used the official Button's tutorial and now everything works just fine. I can't reproduce the issue anymore for no obvious reason!.

Filip Franik · Answer 1 · 2019-09-23T08:13:09.087

Connect both Pin2 and Pin3 with two 1K resistors to ground.

When a pin that's set as INPUT is "floating" (it's not connected to anything) the value on it is "undetermined" and interrupt can trigger when a neighboring pin status changes, or even just magically by itself. The 1K resistors (called pulldown resistors) will make sure that pin is set to LOW when it's not connected using the jumper.

This circuit should put a stable 0V on Pin3 when switch is unpressed and 5V when it's pressed. You should be able to verify that using any voltage meter.

If the issue persists then swapping the microcontroller on the Arduino is just one of the steps you need to perform. You would also need to burn a bootloader on the chip. It's not a hard procedure but it requires a second Arduino.

Duncan C · Answer 2 · 2019-09-24T13:49:03.870

CMOS inputs "float" when not connected to anything, and will give semi-random values. You can either connect the pin to ground via a medium value resistor (1kΩ-10kΩ), or set the pin to INPUT_PULLUP mode.

You shouldn't move the interrupt pin connections around while the Arduino is running. As soon as you disconnect the wire from the input, it begins floating again, and can detect semi-random HIGH/LOW values.

If you use an external pull-down resistor, put a connector after the ground connection and move that connection, so the pull-down resistor is always connected to the pin.

If you use INPUT_PULLUP mode, you should not use a pull down or pull up resistor. This mode connects the pin weakly to +5V, which will hold it at a HIGH value when not connected to anything. You would then ground it to trigger an interrupt. In INPUT_PULLUP mode you can probably disconnect the wire from the interrupt pin without triggering interrupts.

Interrupt is activated as soon as I insert a jumper wire into the port

2 Answers2