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// By Kyle McDonald
// From the instructables project at:
#define resolution 8
#define mains 50
// 60: north america, japan; 50: most other places
#define refresh 2 * 1000000 / mains
void
setup
()
{
Serial
.
begin
(
115200
);
// unused pins are fairly insignificant,
// but pulled low to reduce unknown variables
for
(
int
i
=
2
;
i
<
14
;
i
++
)
{
pinMode
(
i
,
OUTPUT
);
digitalWrite
(
i
,
LOW
);
}
for
(
int
i
=
8
;
i
<
11
;
i
++
)
pinMode
(
i
,
INPUT
);
startTimer
();
}
void
loop
()
{
Serial
.
print
(
time
(
8
,
B00000001
),
DEC
);
Serial
.
print
(
" "
);
Serial
.
print
(
time
(
9
,
B00000010
),
DEC
);
Serial
.
print
(
" "
);
Serial
.
println
(
time
(
10
,
B00000100
),
DEC
);
}
long
time
(
int
pin
,
byte
mask
)
{
unsigned
long
count
=
0
,
total
=
0
;
while
(
checkTimer
()
<
refresh
)
{
// pinMode is about 6 times slower than assigning
// DDRB directly, but that pause is important
pinMode
(
pin
,
OUTPUT
);
PORTB
=
0
;
pinMode
(
pin
,
INPUT
);
while
((
PINB
&
mask
)
==
0
)
count
++
;
total
++
;
}
startTimer
();
return
(
count
<<
resolution
)
/
total
;
}
extern
volatile
unsigned
long
timer0_overflow_count
;
void
startTimer
()
{
timer0_overflow_count
=
0
;
TCNT0
=
0
;
}
unsigned
long
checkTimer
()
{
return
((
timer0_overflow_count
<<
8
)
+
TCNT0
)
<<
2
;
}