Has anyone calculated sunrise/sunset times on an Arduino? I need sunrise/sunset calculations for my sprinkler and home lighting control. :) :) :)

Couldn't you just use a sensor to measure light (e.g. photoresistor)?

- Brian

How do you differentiate from a sunny day and a cloudy day with a photoresistor?

I need the exact sunrise & sunset times per latitude/longitude/GMT locations for automatic home automation control.

Since I already have a RTC (DS1307) and a SPI connected floating point processor (Micromega FPU V3.1) I will try to find a solution using the algorithm below.

Sunrise/Sunset Algorithm

Source:

Almanac for Computers, 1990

published by Nautical Almanac Office

United States Naval Observatory

Washington, DC 20392

Inputs:

day, month, year: date of sunrise/sunset

latitude, longitude: location for sunrise/sunset

zenith: Sun’s zenith for sunrise/sunset

offical = 90 degrees 50’

civil = 96 degrees

nautical = 102 degrees

astronomical = 108 degrees

NOTE: longitude is positive for East and negative for West

NOTE: the algorithm assumes the use of a calculator with the

trig functions in “degree” (rather than “radian”) mode. Most

programming languages assume radian arguments, requiring back

and forth convertions. The factor is 180/pi. So, for instance,

the equation RA = atan(0.91764 * tan(L)) would be coded as RA

= (180/pi)*atan(0.91764 * tan((pi/180)*L)) to give a degree

answer with a degree input for L.

- first calculate the day of the year

N1 = floor(275 * month / 9)

N2 = floor((month + 9) / 12)

N3 = (1 + floor((year - 4 * floor(year / 4) + 2) / 3))

N = N1 - (N2 * N3) + day - 30

- convert the longitude to hour value and calculate an approximate time

lngHour = longitude / 15

if rising time is desired:

t = N + ((6 - lngHour) / 24)

if setting time is desired:

t = N + ((18 - lngHour) / 24)

- calculate the Sun’s mean anomaly

M = (0.9856 * t) - 3.289

- calculate the Sun’s true longitude

L = M + (1.916 * sin(M)) + (0.020 * sin(2 * M)) + 282.634

NOTE: L potentially needs to be adjusted into the range [0,360) by adding/subtracting 360

5a. calculate the Sun’s right ascension

RA = atan(0.91764 * tan(L))

NOTE: RA potentially needs to be adjusted into the range [0,360) by adding/subtracting 360

5b. right ascension value needs to be in the same quadrant as L

Lquadrant = (floor( L/90)) * 90

RAquadrant = (floor(RA/90)) * 90

RA = RA + (Lquadrant - RAquadrant)

5c. right ascension value needs to be converted into hours

RA = RA / 15

- calculate the Sun’s declination

sinDec = 0.39782 * sin(L)

cosDec = cos(asin(sinDec))

7a. calculate the Sun’s local hour angle

cosH = (cos(zenith) - (sinDec * sin(latitude))) / (cosDec * cos(latitude))

if (cosH > 1)

the sun never rises on this location (on the specified date)

if (cosH < -1)

the sun never sets on this location (on the specified date)

7b. finish calculating H and convert into hours

if if rising time is desired:

H = 360 - acos(cosH)

if setting time is desired:

H = acos(cosH)

H = H / 15

- calculate local mean time of rising/setting

T = H + RA - (0.06571 * t) - 6.622

- adjust back to UTC

UT = T - lngHour

NOTE: UT potentially needs to be adjusted into the range [0,24) by adding/subtracting 24

- convert UT value to local time zone of latitude/longitude

localT = UT + localOffset

Other notes:

I found an Application Note #38 (Calculating Sunrise/sunset times) at Micromega's corp website: http://www.micromegacorp.com/appnotes.html. There is even source code there for a Basic Stamp which has to be converted to the Arduino.

There is also an Arduino library made for this floating point processor. (FPU V 3.1)

The Arduino is a very good microcontroller but when it comes to floating point calculations the speed and the resources required will crushed it so additional muscle of a floating point processor is needed. 8-) 8-) 8-)