Micro switches can with motors to detect when it has reached the end of movement, such as in a 3D printer to stop the motor going too far over the end, or to detect if a drawcircuit is open or closed. An open circuit is off and a closed circuit is on. When a circuit is normally open, it means the device is by default off and will only turn on when it receives a HIGH/1/TRUE signal from the microcontroller. Vice versa, when a circuit is normally closed, it means the device is by default on and will only turn off when it receives a HIGH/1/TRUE signal from the microcontroller

Wiring

Wiring

up
• VCC/+ buttons- and5V
switches
• GND/- is- simple,GND
however
• IN/SIG there- ispin a3
complexity
• NO you- mightred(+) notwire have thought about.

  Although a push button like that inof the diagramwater onlypump

has
• COM two- connections, which are closed by pressing the button, you have to add a resistor to make the circuit work properly.

  When the button is pressed the current on one side is able to flow to the other, however when the button is released the circuit is broken and thered(+) wire toof thebattery

Arduino is known as floating, the voltage is indeterminate, so we need to connect it to ground to ensure the Arduino reads 0V.



It's not possible however to do this otherwise when you apply 5V by closing the circuit you would create a short circuit, instead we

• connect the Arduinoblack(-) pinwire through a high value 10KΩ resistor to ground, this allowsof the circuitwater topump quicklyand reachblack(-) 0V when the button is released but prevents large amountswire of currentbattery flowingtogether
when the button is pressed.

Getting started

The following is a simple circuitcode that will get your button controllingmake the LEDwater builtpump intoturn theon Arduino.for 1 second and off for 1 second.

#defineconst ledPinint 13RELAY_PIN #define= buttonPin3;  4// the Arduino pin, which connects to the IN pin of relay

// the setup function runs once when you press reset or power the board
void setup() {
  pinMode(// ledPin,initialize OUTPUTdigital );pin as an output.
  pinMode(RELAY_PIN, buttonPin, INPUT )OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  booleandigitalWrite(RELAY_PIN, btnState = digitalRead( buttonPin )HIGH); if//turn (on
  btnState == HIGH ) {delay(1000);
  digitalWrite(RELAY_PIN, ledPin, HIGH )LOW); }//turn elseoff
  {
    digitalWrite( ledPin, LOW )delay(1000);
  }
}

If you want to add a toggle functionality such that one press causes the LED to come on, and another press then turns it off, so you don't have to hold the button down things get a little bit more complex.

The Arduino is a powerful computer and operates many times faster than human perception, as such when the mechanical push button is closed there is a small amount of 'bounce' where the circuit makes and breaks the connection a few times before it settles, this is detected by the Arduino as multiple presses.

This diagram shows the signal bouncing up and down over a period of 10µS (0.00001 seconds)

In effect this means that each time you press the button to toggle just once it toggles multiple times, you can fix this either with a small capacitor, or modifications to your Arduino sketch.

The code here adds two major changes, first it tracks the current and previous button state through each loop meaning it can see if the button has changed from LOW to HIGH, and then adds a delay of 75ms to allow the button to settle but keep it fast enough that the user doesn't perceive this delay.

#define ledPin 13
#define buttonPin 4

boolean ledState = LOW;
boolean prevBtnState = LOW;

void setup() {
  pinMode( ledPin, OUTPUT );
  pinMode( buttonPin, INPUT );
}

void loop() {
  boolean btnState = digitalRead( buttonPin );

  if ( btnState == HIGH && prevBtnState == LOW ) {
    ledState = ! ledState;
    delay( 75 );
  }

  digitalWrite( ledPin, ledState );

  prevBtnState = btnState;
}