Hardware Reference
In-Depth Information
If
switchState
is high or connected to 5 volts…
…print “The switch is on!” via serial.
If
switchState
is low or connected to ground…
…print “The switch is off!” via serial.
Pause for half a second to slow down the output of the sketch.
When you upload this code to Galileo and open the serial monitor, you should
see
The switch is off!
printed repeatedly in the window. Push down on the
switch and it should change!
digitalRead()
The main takeaway from
Example 4-1
is the use of
digitalRead()
, which
checks the value of the pin provided in the parameters. In this case, you pro-
vided the variable
switchInputPin
, which evaluates to 2. After checking to
see if pin 2 is connected to 5 volts or ground,
digitalRead()
returns either
HIGH or LOW respectively. That value is stored in a new variable called
switchState
.
You may be wondering: HIGH and LOW aren't integers, so why
are we storing them as variables with the type
int
? The reason
is that Galileo thinks of high and low as the integers 1 and 0
and therefore
HIGH
and
LOW
are defined to mean 1 and 0 re-
spectively in Arduino code. This makes the code a little bit
easier to read and understand.
To prove that
HIGH
and
LOW
are equivalent to 1 and 0, try using
Serial.println()
to print the value of
HIGH + HIGH
to the serial
monitor.
You can also see that you used
pinMode()
to set pin 2 as an input in the setup
function. You're required to do this if you want to use
digitalRead()
on that
pin.
The syntax of
digitalRead()
is:
digitalRead(pin);
The parameter of
digitalRead
is:
•
pin
: the input pin number you want to read
digitalRead()
returns HIGH or LOW.
