OK, I will admit that I am a little obsessed with things Mayan at the moment, which explains why I wanted to make a Mayan Tzolkin calendar. I modeled the general layout and fabrication on the very nice Sleek Word Clock by scottbez1 which you can see here: https://www.instructables.com/id/Sleek-word-clock/?ALLSTEPS.

You can read about the Tzolkin Mayan calendar on Wikipedia http://en.wikipedia.org/wiki/Tzolk%27in. It is one of several calendars, and consists of 13 numbers and 20 day signs which appear in 260 combinations that rotate. In other words, with every change of the day the numer increases from 1 to 13 and then back to 1 again. Similarly the 20 day signs rotate. 

What I needed was a frame and face with the numbers and day signs on it, which I modeled on the Sleek World Clock, and relied on scottbez1's great instructions on printing the face and making the actual calendar. The electronics are Arduino and I put the code together from bits and pieces to take the date from an RTC, calculate the Julian Date and then work out where in the two Tzolkin rotation that day falls. LED's are controlled via a shift register. 

This is my first ever Arduino project - a testament to the great ease of use of this amazing technology! 

Step 1: Assembling the Electronics on the Breadboard for Testing

1 Ikea RIBBA shadow box - $10

18 white, 5 red, 5 blue, 5 yellow LEDs (www.sparkfun.com SuperBright $0.50 each when bought in packs of 100) - $17
33 Resistors 330 Ohm 1/6th Watt - $2
1 Arduino Uno - R3 board www.sparkfun.com - $30
1 Real Time Clock Module DS1307 BOB-00099 www.sparkfun.com - $15
5 Shift Register 8-Bit - 74HC595 www.sparkfun.com - $7
1 Wall Adapter Power Supply - 9VDC 650mA www.sparkfun.com - $6

2 printed transparencies (see attached pdf on Step 2) - $1

Total cost: $88

Also: prototyping breadboards, prototyping leads, wire etc
Cardboard and other household items

Total cost: around $44 (using standalone ATMega168) or $67 (if you buy a full Arduino)

Just wanted to say that it is a very cool time clock you did and also love Mayan stuff
Great looking project, and a really nice writeup, too! You've got a terrific level of detail here, which means other people could easily replicate it or even use it as a launching point for their own calendars/clocks. <br> <br>In addition to the Tzolk'in (agricultural?) cycle, I guess that this could be expanded to include the <a href="http://en.wikipedia.org/wiki/Haab%27" rel="nofollow">Haab' (365-day solar year) cycle</a>, and even a long-count (essentially, Julian number :-) index. <br> <br>The Haab' would probably be most easily done with a separate, second construction, with an appropriate display panel. <br> <br>The Long Count is much simpler computationally, using the Julian date with an offset for the Mayan epoch (something in 3114 BC, as I recall), and then just doing a series of modulo-20 and modulo-18 calculations. The display (with at least five digit positions) would probably have to be done differently, either with servos rotating the glyphs into position, or with maybe multi-pixel displays. <br>
Thanks for the kind comments. I agree - an expanded version would be fun to make. What I learned from this project is that the physical making of the object was the most challenging (for me). I had alot of wires and soldering and LED wrangling. There must be more elegant ways to work, and I will try it again with a better approach. That would be a good time to bring in the additional calendars.
I'm not so sure about &quot;more elegant.&quot; What you described is pretty much how projects like this work :-) You might have been able to do the LED's more stably by making a custom circuit board with holes to position them, rather than soldering the LED and resistor leads directly. <br> <br>In any event, this sounds like it was a lot of fun for you, and tied learning a new set of skills to something in which you were already interested. Congratulations!
I do have a question. Where did you get your Julian date function? It doesn't look quite right to me. The algorithm I'm familiar with is equivalent to the one <a href="http://en.wikipedia.org/wiki/Julian_date#Calculation" rel="nofollow">in Wikipedia</a>, which doesn't look the same as yours.
Hi kelseymh - I got the function from this thread:<br>http://arduino.cc/forum/index.php?topic=94925.0<br><br>You will see the exact code I used there, a little lower down.<br><br>I looked at the Wikipedia page, but the math was too challenging for me ;-(<br><br>For my purposes it may not be that critical to get the exact correct date, as the ultimate goal is to use Julian Date to calculate the Tzolkin state. <br><br>Oliver

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