Reference.Constants History

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February 11, 2014, at 04:57 AM by Scott Fitzgerald - added information about LED_BUILTIN
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to:

LED_BUILTIN

Most Arduino boards have a pin connected to an on-board LED in series with a resistor. LED_BUILTIN is a drop-in replacement for manually declaring this pin as a variable. Most boards have this LED connected to digital pin 13.

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May 24, 2012, at 10:53 PM by Scott Fitzgerald -
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The Atmega chip on the Arduino has internal pull-up resistors (resistors that connect to power internally) that you can access. If you prefer to use these instead of external pull-down resistors, you can use the INPUT_PULLUP argument in pinMode(). This effectively inverts the behavior, where HIGH means the sensor is off, and LOW means the sensor is on. See the Digital Input Pullup? tutorial for an example of this in use.

to:

The Atmega chip on the Arduino has internal pull-up resistors (resistors that connect to power internally) that you can access. If you prefer to use these instead of external pull-down resistors, you can use the INPUT_PULLUP argument in pinMode(). This effectively inverts the behavior, where HIGH means the sensor is off, and LOW means the sensor is on. See the Input Pullup Serial tutorial for an example of this in use.

Deleted line 68:
May 07, 2012, at 05:39 PM by Tom Igoe -
May 07, 2012, at 05:39 PM by Tom Igoe -
Changed lines 40-41 from:

Digital pins can be used as INPUT, INPUT_PULLUP, or OUTPUT. Changing a pin with pinMode() drastically changes the electrical behavior of the pin.

to:

Digital pins can be used as INPUT, INPUT_PULLUP, or OUTPUT. Changing a pin with pinMode() changes the electrical behavior of the pin.

Changed lines 44-45 from:

Arduino (Atmega) pins configured as INPUT with pinMode() are said to be in a high-impedance state. One way of explaining this is that pins configured as INPUT make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

to:

Arduino (Atmega) pins configured as INPUT with pinMode() are said to be in a high-impedance state. Pins configured as INPUT make extremely small demands on the circuit that they are sampling, equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

March 28, 2012, at 03:00 PM by Scott Fitzgerald -
Changed lines 42-43 from:

Pins Configured as Inputs

to:

Pins Configured as INPUT

Changed lines 48-49 from:

The Atmega chip on the Arduino has internal pull-up resistors (resistors that connect to power internally) that you can access. If you prefer to use these instead of external pull-down resistors, you can use the INPUT_PULLUP argument in pinMode(). This effectively inverts the behavior, where HIGH means the sensor is off, and LOW means the sensor is on.

to:

Pins Configured as INPUT_PULLUP

The Atmega chip on the Arduino has internal pull-up resistors (resistors that connect to power internally) that you can access. If you prefer to use these instead of external pull-down resistors, you can use the INPUT_PULLUP argument in pinMode(). This effectively inverts the behavior, where HIGH means the sensor is off, and LOW means the sensor is on. See the Digital Input Pullup? tutorial for an example of this in use.

Deleted line 69:
March 14, 2012, at 11:50 PM by Scott Fitzgerald - INPUT_PULLUP work
Changed lines 46-49 from:

Unfortunately pins with high-impedance state makes them affected to catching noise and picking up false signals. You can avoid this effect by placing a resistor between the Vcc and the input pin. The resistor will normally hold the input pin at logic HIGH. Any external source can pull the voltage down to LOW when required.

The Atmega chip on the Arduino has internal pull-up resistors. If you prefer to use these instead of external resistors, you can use the INPUT_PULLUP argument in pinMode().

to:

If you have your pin configured as an INPUT, you will want the pin to have a reference to ground, often accomplished with a pull-down resistor (a resistor going to ground) as described in the Digital Read Serial tutorial.

The Atmega chip on the Arduino has internal pull-up resistors (resistors that connect to power internally) that you can access. If you prefer to use these instead of external pull-down resistors, you can use the INPUT_PULLUP argument in pinMode(). This effectively inverts the behavior, where HIGH means the sensor is off, and LOW means the sensor is on.

March 14, 2012, at 07:34 PM by Scott Fitzgerald - added information on INPUT_PULLUP
Changed lines 16-19 from:

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.

Note that the true and false constants are typed in lowercase unlike HIGH, LOW, INPUT, & OUTPUT.

to:

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is true, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.

Note that the true and false constants are typed in lowercase unlike HIGH, LOW, INPUT, & OUTPUT.

Changed lines 28-29 from:

A pin may also be configured as an INPUT with pinMode, and subsequently made HIGH with digitalWrite, this will set the internal 20K pullup resistors, which will steer the input pin to a HIGH reading unless it is pulled LOW by external circuitry.

to:

A pin may also be configured as an INPUT with pinMode, and subsequently made HIGH with digitalWrite, this will set the internal 20K pullup resistors, which will steer the input pin to a HIGH reading unless it is pulled LOW by external circuitry. This is how INPUT_PULLUP works as well

Changed lines 38-41 from:

Defining Digital Pins, INPUT and OUTPUT

Digital pins can be used either as INPUT or OUTPUT. Changing a pin from INPUT to OUTPUT with pinMode() drastically changes the electrical behavior of the pin.

to:

Defining Digital Pins, INPUT, INPUT_PULLUP, and OUTPUT

Digital pins can be used as INPUT, INPUT_PULLUP, or OUTPUT. Changing a pin with pinMode() drastically changes the electrical behavior of the pin.

Changed lines 48-49 from:

The pull-up resistor could be an external resistor that you connect externally or since the Arduino (Atmega) has already included internal pull-up resistors, you can enable them by choosing the INPUT_PULLUP argument inside the pinMode() function.

to:

The Atmega chip on the Arduino has internal pull-up resistors. If you prefer to use these instead of external resistors, you can use the INPUT_PULLUP argument in pinMode().

Deleted line 68:
March 14, 2012, at 01:00 PM by Federico -
Changed lines 40-41 from:

Digital pins can be used either as INPUT or OUTPUT. Changing a pin from INPUT TO OUTPUT with pinMode() drastically changes the electrical behavior of the pin.

to:

Digital pins can be used either as INPUT or OUTPUT. Changing a pin from INPUT to OUTPUT with pinMode() drastically changes the electrical behavior of the pin.

Added lines 46-49:

Unfortunately pins with high-impedance state makes them affected to catching noise and picking up false signals. You can avoid this effect by placing a resistor between the Vcc and the input pin. The resistor will normally hold the input pin at logic HIGH. Any external source can pull the voltage down to LOW when required.

The pull-up resistor could be an external resistor that you connect externally or since the Arduino (Atmega) has already included internal pull-up resistors, you can enable them by choosing the INPUT_PULLUP argument inside the pinMode() function.

October 18, 2008, at 04:48 PM by Paul Badger -
Added lines 28-29:

A pin may also be configured as an INPUT with pinMode, and subsequently made HIGH with digitalWrite, this will set the internal 20K pullup resistors, which will steer the input pin to a HIGH reading unless it is pulled LOW by external circuitry.

October 18, 2008, at 04:41 PM by Paul Badger -
Changed lines 34-35 from:

When a pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, i.e. light an LED that is connected through a series resistor to, +5 volts, or to another pin configured as an output, and set to HIGH.

to:

When a pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, e.g. light an LED that is connected through a series resistor to, +5 volts, or to another pin configured as an output, and set to HIGH.

May 10, 2008, at 06:57 AM by David A. Mellis -
Changed lines 26-27 from:

When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report HIGH (0) if a voltage of 3 volts or more is present at the pin.

to:

When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report HIGH if a voltage of 3 volts or more is present at the pin.

Changed lines 32-33 from:

The meaning of LOW also has a different meaning depending on whether a pin is set to INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report LOW (0) if a voltage of 2 volts or less is present at the pin.

to:

The meaning of LOW also has a different meaning depending on whether a pin is set to INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report LOW if a voltage of 2 volts or less is present at the pin.

March 29, 2008, at 05:43 PM by David A. Mellis -
Changed lines 6-7 from:

There are two boolean constants defined in the C language, upon which Arduino is based: TRUE and FALSE.

to:

There are two constants used to represent truth and falsity in the Arduino language: true, and false.

March 28, 2008, at 02:48 AM by Paul Badger -
Changed lines 41-42 from:

Arduino (Atmega) pins configured as INPUT are said to be in a high-impedance state. One way of explaining this is that pins configured as INPUT make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

to:

Arduino (Atmega) pins configured as INPUT with pinMode() are said to be in a high-impedance state. One way of explaining this is that pins configured as INPUT make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

Changed lines 45-47 from:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can source (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails. The amount of current provided by an Atmega pin is also not enough to power most relays or motors, and some interface circuitry will be required.

to:

Pins configured as OUTPUT with pinMode() are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can source (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for reading sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails. The amount of current provided by an Atmega pin is also not enough to power most relays or motors, and some interface circuitry will be required.

March 28, 2008, at 02:45 AM by Paul Badger -
Changed lines 27-28 from:

When an output pin is configured to OUTPUT with pinMode, and set to HIGH with digitalWrite, the pin is at 5 volts. In this state it can source current, i.e. light an LED that is connected through a series resistor to ground, or to another pin configured as an output, and set to LOW.

to:

When a pin is configured to OUTPUT with pinMode, and set to HIGH with digitalWrite, the pin is at 5 volts. In this state it can source current, e.g. light an LED that is connected through a series resistor to ground, or to another pin configured as an output, and set to LOW.

Changed lines 31-33 from:

The meaning of LOW also has a different meaning depending on whether a pin is set to INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report LOW (0) if a voltage of 2 volts or less is present at the pin.

to:

The meaning of LOW also has a different meaning depending on whether a pin is set to INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report LOW (0) if a voltage of 2 volts or less is present at the pin.

March 28, 2008, at 02:43 AM by Paul Badger -
Changed line 24 from:

The meaning of HIGH has a somewhat different meaning depending on whether a pin is set to an INPUT or OUTPUT.

to:

The meaning of HIGH (in reference to a pin) is somewhat different depending on whether a pin is set to an INPUT or OUTPUT.

March 18, 2008, at 04:40 AM by Paul Badger -
Added lines 8-9:

false

Changed lines 12-13 from:

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense. Consequently true is often said to be defined as "non-zero".

to:

true

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.

Deleted line 18:
March 17, 2008, at 05:18 PM by Paul Badger -
Changed line 27 from:

The meaning of LOW also has a different meaning depending on whether the pin is set to INPUT or OUTPUT.

to:

The meaning of LOW also has a different meaning depending on whether a pin is set to INPUT or OUTPUT.

March 17, 2008, at 05:16 PM by Paul Badger -
Changed lines 10-11 from:

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense. Consequently true is often said to be defined as non-zero.

to:

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense. Consequently true is often said to be defined as "non-zero".

March 17, 2008, at 05:16 PM by Paul Badger -
Changed lines 10-11 from:

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.

to:

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense. Consequently true is often said to be defined as non-zero.

March 17, 2008, at 05:14 PM by Paul Badger -
Changed line 27 from:

The meaning of LOW has a somewhat different meaning depending on whether the pin is set to INPUT or OUTPUT.

to:

The meaning of LOW also has a different meaning depending on whether the pin is set to INPUT or OUTPUT.

March 17, 2008, at 05:12 PM by Paul Badger -
Changed lines 18-19 from:

HIGH

to:

HIGH

Changed lines 25-26 from:

LOW

to:

LOW

March 17, 2008, at 05:12 PM by Paul Badger -
Changed line 5 from:

Defining Logical Levels, TRUE and FALSE (Boolean Constants)

to:

Defining Logical Levels, true and false (Boolean Constants)

Changed lines 8-9 from:

FALSE is the easier of the two to define. FALSE is defined as 0 (zero).

to:

false is the easier of the two to define. false is defined as 0 (zero).

Changed lines 12-14 from:
to:

Note that the true and false constants are typed in lowercase unlike HIGH, LOW, INPUT, & OUTPUT.

March 17, 2008, at 05:08 PM by Paul Badger -
Changed lines 5-12 from:

Defining Logical Levels, true and false (Boolean Constants)

There are two boolean constants defined in the C language, upon which Arduino is based: true and false.

false is the easier of the two to define. false is defined as 0 (zero).

true is often said to be defined as 1, which is true, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.

to:

Defining Logical Levels, TRUE and FALSE (Boolean Constants)

There are two boolean constants defined in the C language, upon which Arduino is based: TRUE and FALSE.

FALSE is the easier of the two to define. FALSE is defined as 0 (zero).

true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.

Changed lines 16-18 from:

HIGH represents the programming equivalent to 5 volts. When reading the value at a digital pin if there is 3 volts or more at the input pin, the microprocessor will understand it as HIGH. This constant is also represented by the integer number 1.

LOW represents the programming equivalent to 0 volts. The meaning of LOW has a somewhat different meaning depending on whether the pin is set to an INPUT or OUTPUT.

to:

HIGH The meaning of HIGH has a somewhat different meaning depending on whether a pin is set to an INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report HIGH (0) if a voltage of 3 volts or more is present at the pin.

When an output pin is configured to OUTPUT with pinMode, and set to HIGH with digitalWrite, the pin is at 5 volts. In this state it can source current, i.e. light an LED that is connected through a series resistor to ground, or to another pin configured as an output, and set to LOW.

LOW The meaning of LOW has a somewhat different meaning depending on whether the pin is set to INPUT or OUTPUT.

Changed lines 26-27 from:

When an output pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, i.e. light an LED that is connected through a series resistor to +5 volts, or to another pin configured as an output, and set to HIGH.

to:

When a pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, i.e. light an LED that is connected through a series resistor to, +5 volts, or to another pin configured as an output, and set to HIGH.

Changed lines 38-40 from:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails.

to:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can source (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails. The amount of current provided by an Atmega pin is also not enough to power most relays or motors, and some interface circuitry will be required.

March 17, 2008, at 04:59 PM by Paul Badger -
Changed lines 21-22 from:

Setting an output pin to low with digitalWrite, means that the pin is at 0 volts. In this state it can sink current, i.e. light an LED that is connected through a series resistor to +5 volts, or to another pin configured as an output, and set to HIGH.

to:

When an output pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, i.e. light an LED that is connected through a series resistor to +5 volts, or to another pin configured as an output, and set to HIGH.

March 17, 2008, at 04:57 PM by Paul Badger -
Changed lines 18-20 from:

LOW represents the programming equivalent to 0 volts. The meaning of LOW has a somewhat different meaning, depending on whether the pin is set to an input or output. When reading a pin is set to an input with digitalRead, if a voltage of 2 volts or less is present at the pin, the microcontroller will report LOW (0).

to:

LOW represents the programming equivalent to 0 volts. The meaning of LOW has a somewhat different meaning depending on whether the pin is set to an INPUT or OUTPUT. When a pin is configured as an INPUT with pinMode, and read with digitalRead, the microcontroller will report LOW (0) if a voltage of 2 volts or less is present at the pin.

March 17, 2008, at 04:55 PM by Paul Badger -
Changed lines 18-19 from:

LOW is representing the programming equivalent to 0 volts. When reading the value at a digital pin, if we get 2 volts or less, the microprocessor will understand it as LOW. This constant if also represented by the integer number 0.

to:

LOW represents the programming equivalent to 0 volts. The meaning of LOW has a somewhat different meaning, depending on whether the pin is set to an input or output. When reading a pin is set to an input with digitalRead, if a voltage of 2 volts or less is present at the pin, the microcontroller will report LOW (0).

Setting an output pin to low with digitalWrite, means that the pin is at 0 volts. In this state it can sink current, i.e. light an LED that is connected through a series resistor to +5 volts, or to another pin configured as an output, and set to HIGH.

March 17, 2008, at 04:45 PM by Paul Badger -
Changed line 5 from:

Defining Logical Levels, true and false (Boolean Constants)

to:

Defining Logical Levels, true and false (Boolean Constants)

Changed line 13 from:

Defining Pin Levels, HIGH and LOW

to:

Defining Pin Levels, HIGH and LOW

Changed lines 20-21 from:

Defining Digital Pins, INPUT and OUTPUT

to:

Defining Digital Pins, INPUT and OUTPUT

Changed lines 28-29 from:
Pins Configured as Outputs
to:

Pins Configured as Outputs

March 17, 2008, at 04:45 PM by Paul Badger -
Changed lines 24-25 from:
Pins Configured as Inputs
to:

Pins Configured as Inputs

March 17, 2008, at 04:44 PM by Paul Badger -
Changed lines 24-25 from:

Pins Configured as Inputs

to:
Pins Configured as Inputs
Changed lines 28-29 from:

Pins Configured as Outputs

to:
Pins Configured as Outputs
March 17, 2008, at 04:14 PM by Paul Badger -
Changed line 5 from:

Defining Logical Levels, true and false (Boolean Constants)

to:

Defining Logical Levels, true and false (Boolean Constants)

Changed line 13 from:

Defining Pin Levels, HIGH and LOW

to:

Defining Pin Levels, HIGH and LOW

Changed lines 20-21 from:

Defining Digital Pins, INPUT and OUTPUT

to:

Defining Digital Pins, INPUT and OUTPUT

January 21, 2008, at 05:57 PM by David A. Mellis -
Changed lines 16-19 from:

HIGH represents the programming equivalent to 5 volts. When reading the value at a digital pin if there is 3 volts or more at the input pin, the microprocessor will understand it as HIGH. This constant is also represented by the integer number 1, and also the truth level TRUE.

LOW is representing the programming equivalent to 0 volts. When reading the value at a digital pin, if we get 2 volts or less, the microprocessor will understand it as LOW. This constant if also represented by the integer number 0, and also the truth level FALSE.

to:

HIGH represents the programming equivalent to 5 volts. When reading the value at a digital pin if there is 3 volts or more at the input pin, the microprocessor will understand it as HIGH. This constant is also represented by the integer number 1.

LOW is representing the programming equivalent to 0 volts. When reading the value at a digital pin, if we get 2 volts or less, the microprocessor will understand it as LOW. This constant if also represented by the integer number 0.

January 21, 2008, at 05:57 PM by David A. Mellis -
Changed lines 5-12 from:

Defining Logical Levels, TRUE and FALSE (Boolean Constants)

There are two boolean constants defined in the C language, upon which Arduino is based: TRUE and FALSE.

FALSE is the easier of the two to define. FALSE is defined as 0 (zero).

TRUE is often said to be defined as 1, which is true, but TRUE has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as TRUE, too, in a Boolean sense.

to:

Defining Logical Levels, true and false (Boolean Constants)

There are two boolean constants defined in the C language, upon which Arduino is based: true and false.

false is the easier of the two to define. false is defined as 0 (zero).

true is often said to be defined as 1, which is true, but true has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense.

June 10, 2007, at 03:47 AM by Paul Badger -
June 10, 2007, at 03:44 AM by Paul Badger -
Changed line 5 from:

Defining Logical Levels (Boolean Constants)

to:

Defining Logical Levels, TRUE and FALSE (Boolean Constants)

Changed line 13 from:

Defining Pin Levels

to:

Defining Pin Levels, HIGH and LOW

Changed lines 20-21 from:

Defining Digital Pins

to:

Defining Digital Pins, INPUT and OUTPUT

June 10, 2007, at 03:33 AM by Paul Badger -
Changed lines 30-33 from:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails. For this reason it is a good idea to connect output pins with 470Ω or 1k resistors.

to:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails.

June 10, 2007, at 03:32 AM by Paul Badger -
Changed lines 5-6 from:

Defining Logical levels (Boolean Constants)

to:

Defining Logical Levels (Boolean Constants)

There are two boolean constants defined in the C language, upon which Arduino is based: TRUE and FALSE.

FALSE is the easier of the two to define. FALSE is defined as 0 (zero).

TRUE is often said to be defined as 1, which is true, but TRUE has a wider definition. Any integer which is non-zero is TRUE, in a Boolean sense. So -1, 2 and -200 are all defined as TRUE, too, in a Boolean sense.

Defining Pin Levels

Changed lines 16-17 from:

HIGH is representing the programming equivalent to 5 Volts. When reading the value at a digital pin if we get 3 Volts or more the microprocessor will understad it as HIGH. This constant is also represented the integer number 1, and also the truth level TRUE.

to:

HIGH represents the programming equivalent to 5 volts. When reading the value at a digital pin if there is 3 volts or more at the input pin, the microprocessor will understand it as HIGH. This constant is also represented by the integer number 1, and also the truth level TRUE.

Changed lines 26-27 from:

Arduino (Atmega) pins configured as inputs are said to be in a high-impedance state. One way of explaining this is that pins configured as INPUT make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

to:

Arduino (Atmega) pins configured as INPUT are said to be in a high-impedance state. One way of explaining this is that pins configured as INPUT make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

Changed lines 30-33 from:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors.

to:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors. Pins configured as outputs can also be damaged or destroyed if short circuited to either ground or 5 volt power rails. For this reason it is a good idea to connect output pins with 470Ω or 1k resistors.

May 28, 2007, at 08:24 PM by Paul Badger -
Changed lines 31-41 from:
to:
May 28, 2007, at 08:23 PM by Paul Badger -
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Digital pins can be used either as INPUT or OUTPUT. These values drastically change the electrical behavior of the pins.

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Digital pins can be used either as INPUT or OUTPUT. Changing a pin from INPUT TO OUTPUT with pinMode() drastically changes the electrical behavior of the pin.

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Arduino (Atmega) pins configured as inputs are said to be in a high-impedance state. One way of explaining this is that input pins make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

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Arduino (Atmega) pins configured as inputs are said to be in a high-impedance state. One way of explaining this is that pins configured as INPUT make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

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Pins configured as outputs are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors.

to:

Pins configured as OUTPUT are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors.

May 28, 2007, at 08:20 PM by Paul Badger -
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Constants are predefined variables in the system. They are used to make the programs easier to read. We classify constants in groups.

Defining Logical levels

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Constants are predefined variables in the Arduino language. They are used to make the programs easier to read. We classify constants in groups.

Defining Logical levels (Boolean Constants)

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HIGH is representing the programming equivalent to 5 Volts. When reading the value at a digital pin if we get 3 Volts or more the microprocessor will understad it as HIGH. This constant represents the integer number 1, and also the truth level TRUE.

LOW is representing the programming equivalen to 0 Volts. When reading the value at a digital pin if we get 2 Volts or less the microprocessor will understand it as LOW. This constant represents the integer number 0, and also the truth level FALSE.

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HIGH is representing the programming equivalent to 5 Volts. When reading the value at a digital pin if we get 3 Volts or more the microprocessor will understad it as HIGH. This constant is also represented the integer number 1, and also the truth level TRUE.

LOW is representing the programming equivalent to 0 volts. When reading the value at a digital pin, if we get 2 volts or less, the microprocessor will understand it as LOW. This constant if also represented by the integer number 0, and also the truth level FALSE.

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Digital pins can be used either as INPUT or OUTPUT. These values represent precisely what their meaning stands for.

to:

Digital pins can be used either as INPUT or OUTPUT. These values drastically change the electrical behavior of the pins.

Pins Configured as Inputs

Arduino (Atmega) pins configured as inputs are said to be in a high-impedance state. One way of explaining this is that input pins make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 Megohms in front of the pin. This makes them useful for reading a sensor, but not powering an LED.

Pins Configured as Outputs

Pins configured as outputs are said to be in a low-impedance state. This means that they can provide a substantial amount of current to other circuits. Atmega pins can sorce (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. This makes them useful for powering LED's but useless for connecting to sensors.

See also

May 27, 2007, at 02:43 AM by Paul Badger -
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Constants

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constants

April 16, 2007, at 04:33 PM by Paul Badger -
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March 25, 2006, at 12:40 AM by Jeff Gray -
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Constants

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Constants

January 13, 2006, at 12:48 AM by 82.186.237.10 -
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Digital pins can be used either as INPUT or OUTPUT. These values represent precisely what their meaning stands for.

to:

Digital pins can be used either as INPUT or OUTPUT. These values represent precisely what their meaning stands for.

Reference Home

December 03, 2005, at 08:10 PM by 213.140.6.103 -
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Constants

Constants are predefined variables in the system. They are used to make the programs easier to read. We classify constants in groups.

Defining Logical levels

When reading or writing to a digital pin there are only two possible values a pin can take/be-set-to: HIGH and LOW.

HIGH is representing the programming equivalent to 5 Volts. When reading the value at a digital pin if we get 3 Volts or more the microprocessor will understad it as HIGH. This constant represents the integer number 1, and also the truth level TRUE.

LOW is representing the programming equivalen to 0 Volts. When reading the value at a digital pin if we get 2 Volts or less the microprocessor will understand it as LOW. This constant represents the integer number 0, and also the truth level FALSE.

Defining Digital Pins

Digital pins can be used either as INPUT or OUTPUT. These values represent precisely what their meaning stands for.

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