# Digital Sundial- Ancient Tech in Modern Times

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The digital sundial speaks to the ancient desire of keeping track of time. A desire probably as old as the concept of time itself; fascination which has lead to very advanced machines. Nonetheless, for thousands of years people relied on the sun (at the time thought) moving around the earth. Some of the first documented time tracking devices date back to Egyptian times where they would raise obelisks and look at the morphing shadow as the day went by.

With this project I wanted to build a simple devise capable of taking us back, appreciating the beauty of time.

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## Step 1: Math :)

Making a sun dial is not hard but there are a couple of steps one must go through to make it (relatively) accurate.

Location, location, location. Sun dials are very location specific machines (is a sundial a machine??). First you will need to find where you are on the planet. Now a days that can be very easily solved opening google earth and finding yourself, or even looking at your phone's GPS. Take note of the coordinates, you will need them later, in my case they where 37.80, -122.40.

Having this information you can now calculate three things, the angle of your gnomon, the angles for each hour and true north. Sundials are such ancient devices that using modern tech almost feels out of place, nonetheless, if you want to learn more about shadows and the sun, I would really encourage reading about Eratosthenes and how he calculated the circumference of the earth back around the 200BC!

Using AnyCalculator and the numbers recored you can find the angles you need for each hour. In turn, visiting the NGDC (National Geophysical Data Center) you can find the true north which you will need to orient the sundial correctly. To be quite honest, I don't think you need to know where true north is now a days, you could just use another clock to orient the sundial.

## Step 2: Modeling & 3D Printing

Using Autodesk Inventor I first started tracing the angles on a sketch, then I created planes that went through the hour lines and the gnomon line. The hard part is done! Using each plane, extrude the right number out of it.

I modeled it in two parts so I could adjust for daylight savings and for ease of 3DP. Both files are attached, keep in mind that these are both for SF latitudes (about 37°) I attached both the base and the gnomon, be ware of the scale since they might be a little too big.

## Step 3: Testing!

Who knew... Sundials don't work that well during the night.

When the print came out of the machine the sun had long been hiding, here a quick video of the initial testings.

## Step 4: Outdoor Testing! and Painting

Wouldn't it be amazing to have a huge one built in a park?

In the mean time go build your own!

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## 57 Discussions

It would be interesting to "deform" the physical proportions of the numbers in the dial to compensate for the angle as the light passes through the digit illuminated in the shadow, resulting in the numbers geometric integrity not being compromised. The result would be that the dial may look slightly Dali-esque and potentially artsy, yet the number illuminated in the shadow would be proportionally correct.

I think the simplest way is to put one up in your back yard and simply go out every hour on the hour and mark the base with the hour.

Do one set of hour marks on the summer solstice and one set of hour marks for the winter solstice and connect them.

Then, make a set of marks between the ends for the months as they pass.

2 replies

Michael, maybe the purpose of this build isn't just to do it the in simplest way. On the contrary, doing it this way makes you live a unique experience and develop skills beyond the ordinary. It brings out the creative human living inside of us! :)

I see all these neat (OK, neat is an understatement) ideas but rarely have the equipment (most often just the hardware, not software LOL) it takes to complete them. This project did lead me to find some great brass compass sundials of various sizes and shapes.

This is a fantastic idea and I'd love to have a larger one of these for the back yard.

Congratulations! I remember reading Scientific American magazine back in 1988 or 1989, and in this amateur science column there was a challenge to build a digital Sun clock. This marvelous work of yours made it come true. Brilliant!

That's really cool! What a unique idea! Fantastic! :D

Absolutely incredible! When I first started looking at your instructable, I thought you had a stepper rotating the bar - now I realize you use the rotational angle of the sun to select the appropriate digit - Amazing!! Hats off to a mind expanding project.

I have always wanted to make a giant sundial out of a telephone pole. Now perhaps I will find the inspiration! Thanks!!

I've been meaning to do something like this for a long time. Well done for actually doing it!

You can construct an analemma/equation of time to give you the difference between local time and civil time at any day of the year. In fact you can construct one empirically if you want, but it would take you half a year. You could also just construct one for your latitude. For that matter, one can even make an "analemmatic" sundial that auto corrects., but I digress.

It's very easy to find true North, mimicking one of the ancient methods. Erect a stick or rod where your gnomen will be, use a plumb-bob (pretend you don't own a square level) to ensure it is at right angle to the horizon (I.e is true vertical). Before noon (local time - which is when the shadow is the shortest), observe the shadow it casts, and put a rock at the end of the shadow. Tie a rope to the rod and stretch it out taut to where you put the rock. Tie a nail (or something sharp) I'm the string where the rock is. Scribe an arc from the rock in the direction the shadow will move (yes you could just scribe a circle with the distance from the rod to the rock as the radius). Then you just have to wait. The shadow will shrink away from the arc you scribed until local noon, and then grow back towards the arc. Just when it touches the arc again, put another rock at that location. Now just use your rope and nail to bisect the angle between the two rocks and the rod. That is true north. (If your thinking it will be the opposite of local noon's shadow direction, you'd be right, but practically it's difficult to tell when the sun's shadow stops sharing and begins to grow.) of course, one can scribe a few circles at different times as protection against a cloudy afternoon.