I've always loved watches; not only are they aesthetic and beautiful, but they are functional, precise and useful. An elegant fusion between engineering and art; two normally opposed perspectives, now joined in harmonic unison. However, all technologies like the dial-up internet, the CVT monitor and the abacus, inevitably will become relics of our past with the advent of advancing technology, and have since become less pragmatic for the typical person to own. Unlike these archaic technologies, the wrist watch still thrives on the wrists of many, standing forever as a testament to one of mankind's greatest inventions: the measurement of time.
I suppose it was inevitable that I would design my very own wrist watch. The name for this wrist watch is the ChronosMEGA, a combination the greek word: chronos for time, and MEGA for the ATmega328P processor used.
The below video is a montage that saturates 4 months of development in 4 minutes.
This short video demonstrates the features of the watch and briefly explains how it functions:
1.1. Table of Contents
1.1.1. Section 1: The Design; the Development
This watch wasn't made with beginner experience. If you wish to understand this Instructable, and to construct your own watch like mine with your own interpretation, you must understand at least the following concepts:
This step generically describes how the design of the ChronosMEGA came to be, and gives a simple look at how it operates.
3.1. LED Layout and Encoding Time
The layout of the watch is set up in a circular array of 10 LEDs. Four of the LEDs account for the Hours, and six of the LEDs account of the Minutes. The LEDs count in Binary to display the time on the watch face.
The layout of the LEDs on the watch is as shown:
Here I discuss the design approach to the schematics and the meaning behind the circuits. The power regulation circuitry is the most involved and where I spent most my time for this step.
4.1. The Power Circuitry
The circuitry handling and regulating the power was the most involved portion. The circuit must take in the power of a 3.7V Li-on battery and boost it with a switching regulator to 5V. The switching regulator is shown here:
The logic flow of the SW for the Watch is depicted above. Programming was done entirely in Assembly, implementing the Interrupt, ADCs, Power Management, GPIO and Timer features of the ATmega328P. The reasons I choose Assembly for my programming language was to optimize my program the best I could and because I pride myself in working in the more difficult, lower levels for projects.
5.1. Initial Prototype
Quite a bit of thought went into the design of the board; originally I had some plain layouts, but eventually the circular array idea came to me and I ran with it. I tucked the power supply circuits on the bottom of the back of the board. I planned for the battery to sit behind the board, so I avoided overlapping components to give the watch the thinnest profile possible.
I'll cover the most interesting or obscure components of the board and the layout.
7.1. Arranging the LEDs
A huge goal for this watch was to make it as aesthetic as possible, therefore, the LEDs were arranged to be symmetrical horizontally and vertically. I choose a circular ring because the gentle shape and the rotating movement of the LEDs seemed to contrast the otherwise sharply edged traces and ICs.
7.1.1. Subtle offsets in spacing for a Faster/Slower effect
It may be noticeable that the LEDs are not spaced equal distances apart. This was done on purpose to create a very subtle effect. While the ChronosMEGA is in its IDLE state, a light will be traveling around the watch face. Since the LEDs have different spacings, the light appears to travel faster at the top and bottom, and slower on the left and right sides.
Using Google's Sketchup CAD tool, one can make an awesome virtual model of his or her board. The plugin is called EagleUp. EagleUp works within EAGLE, by extracting each layer and converting it to a script that can be recognized by SketchUp. SketchUp uses the script to build the board for you.
There are plenty of tutorials on EagleUp's website. Their installation page is incredibly comprehensive and easy to understand. Set up takes a few moments but it is not difficult:
8.1. Why use EagleUp to model your board?
I wanted to build a watch case enclosure surrounding the board, so having a virtual board designed would effectively allow me to ensure that the watch case has the tightest and most accurate tolerances possible. Modeling the board also cross checked the accuracy of the wiring and board layout against the virtual ICs, capacitors, resistors and etc. Seeing that the modeled components fit onto the modeled board gave me confidence that the board layout was correct.
8.2. Designing your own Components
You will have to design many of your own components, which can become tedious quickly. The outcome, however is worth it. Shown below is the ATmega328P chip I designed in SketchUp:
Using EAGLE's CAM Processor tool, I exported the board layout to Gerber files, I ordered five boards with a white solder mask from Seeedstudio's Fusion PCB service. The boards are only 0.8mm thick.
All the components were soldered by hand.
Shown below is the Component side of the board completely soldered:
And the Solder side of the board:
The case was designed with Google SketchUp and consists of 3 main components:
• The top bezel
• The bottom plate
• The four buttons
These three components were combined into a single model with connecting rods. This saved on time and money when the design was ordered to be manufactured by Shapeways.
The watch case is made of pure polished Silver.
10.1. The Bottom Plate
10.3. The Four Buttons
Putting the ChronosMEGA completely together proved to be a challenge because the spacial tolerances were incredibly tight.
It also was fun making the final adjustments of the watch and finally seeing my creation in it's complete state.
11.1. Preparing the Watch Case
The watch case arrived to me as a single model unit: with the buttons, and the two case halves connected together with small silver rods. The case was designed this way because it's much cheaper to order one larger model than several smaller models.
Using a dremel, the rods were severed and smoothed down.
Two holes on each gull wing of the bottom plate were drilled and tapped with 4-40 threading by hand. The standoff mounts for the watch board were tapped as well.
The buttons have small flanges that needed to be filed down quite a bit in order to accommodate the size constraints of the case.
Shown below is how the top bezel was prepared before combining the two halves of the watch. Notice how thin the button flanges are, and the tape on the outside of the case to hold the buttons into place.
You can build a ChronosMEGA clone for yourself very easily because everything is prepared for you to order right away with no development on your end. The hardest part you will have to do is surface mount solder all the components and put the case together with the watch. Luckily, surface mount soldering looks much more intimidating than it actually is, and I also walk you through the steps when putting the ChronosMEGA together.
Listed here are a majority of the components you will need to buy:
The Tactile buttons, USB port and Battery can be found here:
The cost to build a clone can be from $100 to $700. This is mostly depending on the type of material you use to make the case and the watch band used.
The steps I will cover here are:
Step 1: Manufacturing the Board:
To have the board manufactured is very easy, in the folder: ChonosMega/GerberFiles/ you will see that there are two folders called: "OSHPark"  and "SeeedStudio" . These two folders contain a .zip containing Gerber files to directly upload to the corresponding company. Either of these companies will make the boards for a low price. To order, click on one of the links at the bottom of the page and follow the instructions.
Even though I provided Gerbers for OSH Park, I recommend going with SeeedStudio because the OSH Park boards are thicker than SeeedStudio, and I cannot guarantee that the model will fit when you finish!
If you want to go through your own board house, you could cross check the existing Gerber files and make sure they conform to the requirements of your board house. If not, then you can open the .brd file in EAGLE and use the CAM Processor tool to build your own Gerber files from the source.
Here are some specs for the board you may need to know while ordering:
The board will cost you anywhere from $30 to $40 depending on the options that you choose with shipping included.
Step 2: Manufacturing the Watch Case
Simply go here for the entire watch case:
Order the model in any available material you like, I chose the polished silver ($188) option.
The cost of this case can run from about $16 to $600 depending on the material you choose.
Step 3: Ordering all the parts
Order all the parts from Digikey and Sparkfun from the BOM provided above.
Total Cost estimate: $114
Note about microscope glass: If you're serious about cloning, I'll send you some of the microscope slides for no charge. I have 50 of these things left over now and I have no idea what else to do with them. Just send me a message and as long as it doesn't cost me much to mail, I'll get them to you. It's much cheaper than you buying the box of slides because you only need one.
Unfortunately the slides are currently unavailable. I still have more slides (Mar15), so message me and I'll send about 5 of them. Just be careful because these things shatter for like, no reason. So when you get them, be sure to take them to a professional to get them cut.
Step 4: Soldering the Top Components
Once you get the board and all the components, you should be ready to solder.
Check the "RequiredTools.xlsx" before you start and try to gather the tools you need before you start. I highly recommend the flux syringe, the flux remover, ESD tweezers, helping hands to aid you while you are soldering. These will save you a big headache and will make the soldering process much easier. These tools will greatly increase the probability of success.
Surface mount soldering is not as intimidating as it appears. I'm not going to talk about how to surface mount solder here because there are way too many incredible tutorials and videos online. Just Google it and you'll have a good idea how to do it. Anyway, now that you have the components and the board, here is the layout for the top. Everything is mostly self explanatory.
For now, only solder the top Component side the board and the buttons:
This is the last part for cloning and you're almost finished. This section requires much patience. If you are not confident with a procedure, then wait! Do not get over zealous here, it is critical you are careful because everything is so delicate at this stage.
Here we will be:
Step 9: Separating the Case
The watch case that you bought off Shapeways is actually a combination of 3 components: the top bezel, the bottom plate and the four buttons. Each of these are connected to the model with silver rods that will need to be eliminated. The pieces should be separated like so:
There is also one more step. For this watch, the battery is sandwiched between the PCB and the bottom plate. The battery also needs to fit in between the two mounting posts, so you will need to eliminate some material of the posts:
Step 10: Tapping and Drilling
Two holes need to be drilled on each gull wing of the bottom plate in such a way that if a machine screw is fed through the top gull wing, then it will enter that hole. The hole must be about 2.3mm or less than the diameter of the 4-40 screw because you will need to tap these holes with 4-40 threading.
You can see in the main image of this page, the holes that I drilled in the gull wings of the bottom plate.
Be sure to take your time and prepare the case well. Give the bottom plate plenty of support and keep the drill very steady. Don't be afraid to purchase additional tools to help you with this.
You will also need to tap the two mounting posts on the bottom plate with 4-40 threading. They hold the board down onto bottom plate.
Step 11: Cutting the glass and applying
At this point you will need to cut the glass to fit inside the case. I would recommend taking the microscope slide to a professional and getting them cut to fit inside the top bezel, as these slides shatter very easily.
When they are cut, apply a small amount of epoxy to the top bezel's lip and gently press the glass in. Allow the top bezel and glass to sit for an extended period of time.
Step 12: Drilling the watch band
Figure out where the watch band will need to be drilled so that when the machine screws pass through it to hold it in place, then it will be secure and straight.
I placed the band in the groove of the top gull wing and marked with a knife where the drill needs to be. I drilled the band with a drill less than 3mm in diameter.
Step 13: Combining everything together
File the flanges of the buttons down so they are very thin. You can see how thin they should be like so:
When you have them filed down, place them into the holes of the top bezel and apply tape to the outside so that they are held still.
Now use the machine screws to screw the board to the bottom plate.
With the two separate components, we'll join them as one by inserting the USB end in first and then wiggling the other end into place.
Here's a video showing how I combined the two pieces:
Now just slide the watch band pieces into place and use the machine screws to hold the whole assembly into place.
Clean and buffer the watch case and leather. Test the buttons and the USB, make sure that the USB cord can connect to the receptacle inside.