A key design element in the OSWatch project has been the display. I spent a lot of R&D time on various displays, my favorites coming from Adafruit.com. Why? Well aside from being an awesome hobbyist store, they provide open source libraries for almost every single one of their major hardware components. I'm much more interested in focusing on building / delivering the final product, so anyone building generic libraries for common components is a friend of mine!
When It came to screens, when you get down to it, there are 3 varibles I care about:
1.) cost ($)
2.) features (color / resolution / etc)
Cost effects the builder's wallet. Features set the bar for how awesome the watch is, and amperage tells me if the watch has a chance of running for my 24 hour no-recharge goal.
Currently I have 3 favorite screens:
This screen is in my current build. It goes for around $25 a piece, looks great, and is light on the amps, provided you don't light up ever pixel all the time. It's also lighter on memory by being monocromatic, as graphic memory for bitmaps, etc. don't require full color data. Plus, with the clear / white watch body, the asthetics go well together.
I have one, but have yet to fully implement it. The basis behind a screen like this is a combination of a standard LCD screen meets a Kindle smartInk screen. Basically the speed of LCD rendering, but with the ultra low power of a e-ink display. For comparison, the monocrome OLED can draw around 30 milliamps to render, while the Sharp screen draws around 4 MICRO Amps. so, ya. A lot less. At that level you can pretty much keep the screen on as long as you want. (I time out the OLED after about 10 seconds). THe largest downside is that is has no lightsource, so you would need to add one, and / or a light sensor to light it up when needed. Also, did I mention its about $40?
Finally we have a color OLED screen. They are a nice size (128x96) and run around $35. Their power drain is around 40 milliamps, depending on your display plans, etc. The board listed also has a microSD card reader which makes it more intersting. Using it will draw more power, but now you can read / write to flash as you will. This can be very useful for graphically intensive apps, especially with the color element, which will take up a lot of memory if you bake in the bitmaps.