Digital Input Pull-Up Resistor

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1/*
2
3  Input Pull-up Serial
4
5  This example demonstrates the use of pinMode(INPUT_PULLUP). It reads a digital
6
7  input on pin 2 and prints the results to the Serial Monitor.
8
9  The circuit:
10
11  - momentary switch attached from pin 2 to ground
12
13  - built-in LED on pin 13
14
15  Unlike pinMode(INPUT), there is no pull-down resistor necessary. An internal
16
17  20K-ohm resistor is pulled to 5V. This configuration causes the input to read
18
19  HIGH when the switch is open, and LOW when it is closed.
20
21  created 14 Mar 2012
22
23  by Scott Fitzgerald
24
25  This example code is in the public domain.
26
27  https://www.arduino.cc/en/Tutorial/InputPullupSerial
28
29*/
30
31void setup() {
32
33  //start serial connection
34
35  Serial.begin(9600);
36
37  //configure pin 2 as an input and enable the internal pull-up resistor
38
39  pinMode(2, INPUT_PULLUP);
40
41  pinMode(13, OUTPUT);
42
43}
44
45void loop() {
46
47  //read the pushbutton value into a variable
48
49  int sensorVal = digitalRead(2);
50
51  //print out the value of the pushbutton
52
53  Serial.println(sensorVal);
54
55  // Keep in mind the pull-up means the pushbutton's logic is inverted. It goes
56
57  // HIGH when it's open, and LOW when it's pressed. Turn on pin 13 when the
58
59  // button's pressed, and off when it's not:
60
61  if (sensorVal == HIGH) {
62
63    digitalWrite(13, LOW);
64
65  } else {
66
67    digitalWrite(13, HIGH);
68
69  }
70}