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diff --git a/docs/source/arduino/constants.rst b/docs/source/arduino/constants.rst deleted file mode 100644 index 49f3933..0000000 --- a/docs/source/arduino/constants.rst +++ /dev/null @@ -1,144 +0,0 @@ -.. _arduino-constants: - -constants -========= - -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, true and false (Boolean Constants) -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -There are two constants used to represent truth and falsity in the -Arduino language: **true**, and **false**. - - - -false ------ - -false is the easier of the two to define. false is defined as 0 -(zero). - - - -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. - - - -Note that the *true* and *false* constants are typed in lowercase -unlike HIGH, LOW, INPUT, & OUTPUT. - - - -Defining Pin Levels, HIGH and LOW -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -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** - - - -The meaning of HIGH (in reference to a pin) is somewhat different -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 if a voltage of 3 volts or -more is present at the pin. - - - -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. - - - -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. - - - -**LOW** - - - -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. - - - -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. - - - -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. - - - -Pins Configured as Inputs -------------------------- - -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. - - - -Pins Configured as Outputs --------------------------- - -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. - - - -See also --------- - - -- `pinMode() <http://arduino.cc/en/Reference/PinMode>`_ -- `Integer Constants <http://arduino.cc/en/Reference/IntegerConstants>`_ -- `boolean variables <http://arduino.cc/en/Reference/BooleanVariables>`_ - - |