DIY Smartwatch: Project Definitions

Now that I've reviewed what the current smartwatch offerings are, it's time to define a set goals for my own version.

Primary Goals:

• Size (<= 45x45x10mm) - Regular watch sizes vary from 34mm to 40mm with larger ones reaching up to 44mm.  The smartwatches on the market tend toward the larger end of the spectrum so I'm going to set a hard limit at 45mm x 45mm size, with a push for smaller.  Thickness is another matter entirely.  Most hobbyist screens on the market need a breakout board which means my watch will need to have two PCBs and a battery sandwiched together.  The commercial offerings average at a thickness of 10mm so I'm going to shoot for around there.
• Connectivity (BLE) - This is a simple one.  My phone supports BLE and battery life is going to be a huge issue so I'm going to try cutting power consumption wherever I can.  BLE is the obvious choice and there are a couple of cheap modules available on eBay.
• Screen ( > 1.25") - This choice will be largely dependent on my power budget and how power hungry the options for screens are.  However, since no screen on any of the watches currently offered is less than 1.25" diagonally, I think that's a good minimum goal to shoot for.  In terms of screen technology I assume I'm going to have to use some sort of OLED or low power LCD since the eInk type displays offered on the hobbyist market are still pretty sparse.  Maybe I'll get lucky, but I would definitely like to have a color screen if at all possible.
• Battery Life (8 hours) - Since I'm attempting to make a nice smartwatch that has similar functionality to commercial offering, I'm obviously going to have to make sacrifices somewhere.  It's probably going to end up being in the battery life category.  I can't afford low power components and don't have the means to solder tiny chips onto a PCB.  I also don't have much choice when it comes to hobby batteries' sizes and shapes so I will be using the best possible options.  All these factors combined means I'm going to set a goal for an 8 hour battery life so it can last through a whole work day.  Worst case scenario, I can get multiple batteries and swap them out when necessary.
• Price (<= $100) - As stated in my previous post, early supporters of the Pebble smartwatch could get one for $100 and that seems like a reasonable amount, so I'll set a hard limit at that price, though hopefully it will end up being cheaper.
• Interactivity - This one is pretty much up in the air.  I'm experienced enough in Android programming that I can do a lot of the settings and notification handling on the phone side of things, but I would like to add some functionality to the watch as well.  If I get lucky I'd like to use a touchscreen but I'm not sure how likely it is to find one in the right size so I'll probably end up with a few tactile switches for selection and most of the controls.  I'd also like notifications to trigger something more noticeable than the screen lighting up so I'd like to add a vibration motor or a status LED as well.  Additionally, I think an accelerometer would be a useful sensor to add since it probably uses negligible power and could be used for gesture recognition and other interfacing ideas.