Why are commands executing on their own?

Question

This is the program I have used. It's working fine. But I don't known why sometimes it operates on its own. It is used to control a welding machine (Arduino is isolated from earthing). When there is a little vibration the code executes a command. This is the code:

int a = 9; //right actuator forward relay 1
int b = 12; //right actuator reverse relay 2 (orange 10)
int c = 10; //left actuator forward relay 4
int d = 11; //left actuator reverse relay 3
int x = 0;
int y = 0;
const int stepPin = 8; // HIGH =DOWN; LOW == UP
const int dirPin = 7;
void setup() {
 pinMode(5, INPUT_PULLUP);
 pinMode(6, INPUT_PULLUP);
 pinMode(a, OUTPUT);
 pinMode(b, OUTPUT);
 pinMode(c, OUTPUT);
 pinMode(d, OUTPUT);
 pinMode(stepPin, OUTPUT);
 pinMode(dirPin, OUTPUT);
 pinMode(4, INPUT_PULLUP);
 pinMode(2, INPUT_PULLUP);
 Serial.begin(9600);
 digitalWrite(b, HIGH);
 digitalWrite(d, HIGH);
 delay(2000);
 digitalWrite(b, LOW);
 digitalWrite(d, LOW);
 delay(1000);
 Serial.println("press the foot swtich"); // Serial Monitor for Debugging
}
void loop() {
 int Val = digitalRead(5); // Actuator 1 Clamping
 int ValR = digitalRead(6);// Actuator 2 Clamping
 int ValS = digitalRead(4);//Stepper Motor anticlockwise
 int ValM = digitalRead(2);//Stepper Motor Clockwise
 if (Val == LOW && x == 0 ) {
 Serial.print("Val000=");
 Serial.println(Val);
 digitalWrite(c, HIGH);
 delay(1750);
 digitalWrite(c, LOW);
 x = 1;
 Val = digitalRead(5);
 Serial.println("fwd");
 Serial.print("Val=");
 Serial.println(Val);
 delay(500);
 }
 if (Val == LOW && x == 1 ) {
 digitalWrite(d, HIGH);
 digitalWrite(b, HIGH);
 delay(2000);
 digitalWrite(d, LOW);
 digitalWrite(b, LOW);
 x = 0;
 Val = digitalRead(5);
 Serial.println("fwd");
 y = 0;
 Serial.print("Val=");
 Serial.println(Val);
 delay(500);
 }
 if (ValR == LOW && y == 0 ) {
 digitalWrite(a, HIGH);
 delay(1350);
 digitalWrite(a, LOW);
 y = 1;
 ValR = digitalRead(6);
 Serial.println("fwd");
 Serial.print("Val=");
 Serial.println(Val);
 delay(500);
 }
 if (ValR == LOW && y == 1 ) {
 digitalWrite(b, HIGH);
 delay(1200);
 digitalWrite(b, LOW);
 y = 0;
 ValR = digitalRead(6);
 Serial.println("fwd");
 Serial.print("Val=");
 Serial.println(Val);
 delay(500);
 }
 if (ValS == HIGH) {
 Serial.println(Val);
 Serial.println("up");
 digitalWrite(dirPin, HIGH);
 // Enables the motor to move in a particular direction
 // Makes 100 pulses for making half cycle rotation
 for (int x = 0; x < 100; x++) {
 digitalWrite(stepPin, HIGH);
 delayMicroseconds(1000);
 digitalWrite(stepPin, LOW);
 delayMicroseconds(1000);
 }
 // Enables the motor to move in a particular direction
 // Makes 200 pulses for making one full cycle rotation
 }
 if (ValM == LOW) {
 Serial.println("down");
 Serial.println(ValR);
 digitalWrite(dirPin, LOW);
 // Enables the motor to move in a particular direction
 // Makes 200 pulses for making one full cycle rotation
 for (int x = 0; x < 100; x++) {
 digitalWrite(stepPin, HIGH);
 delayMicroseconds(1000);
 digitalWrite(stepPin, LOW);
 delayMicroseconds(1000);
 }
 // Enables the motor to move in a particular direction
 // Makes 200 pulses for making one full cycle rotation
 }
}

• Edgar Bonet: 1. By "it operates on its own" do you mean it acts as if the buttons are pressed, including printing the debugging output? 2. The internal pullups enabled by INPUT_PULLUP are quite weak (around 30 kΩ). In a noisy environment, you way want to use stronger external pullups (i.e. lower resistance).
• Karan Shete: yes its act like the button is pressed, on serial debugging also and the machine runs too. Can debouncing solve if yes how can I add it?
• Edgar Bonet: Debouncing may help if it does also deglitching. But it is probably safer to have a clean signal to start with. Thus I would try the weak pullup first. How much distance is there between the buttons and the Arduino board?
• sa_leinad: What exactly is happening? What messages are you seeing on the serial monitor? Could it be loose wires or wires touching? More information will help us help you.
• Edgar Bonet: I would go straight to 1 kΩ. Also, if your buttons are more than, say, 10 cm from the Arduino board, I would wire them with a twisted pair (signal and ground on the same pair) in order to prevent inductive pick-up.

Answer 1

Trying to write a proper answer...

According to your description, it looks like you are victim of inductive noise pickup. The circuit [MCU → Arduino ground pin → foot pedal → Arduino digital input pin → MCU] is a loop that can pick up magnetic flux. If this flux varies, either because the magnetic field varies (ambient electromagnetic noise) or because the geometry of the circuit changes (you move the wires), this will induce an electromagnetic force that can make your Arduino read LOW even when the button is not pressed.

There are two things you can try to overcome this effect:

1. Replace the weak internal pullup of the Arduino by a much stronger external pullup. Something around 1 kΩ should make it quite hard for the noise to pull the signal low.
2. Connect the pedal to the Arduino board using a twisted pair of wires, like the ones found in telephone or network cables. This kind of cable does a good job at minimizing inductive pickup.

• Karan Shete: I will try with 1k resistor. The Button is actually a foot switch at a distance of 10 feet from arduino
• Karan Shete: The problem is same with 1K resistor too.. the wires are shielded properly
• Karan Shete: It only happens when welding gun relay is activated
• Edgar Bonet: The welding gun may be a source of huge electromagnetic noise.
• Karan Shete: what can i do now?