The history of the uWatch mentions the 53mm x 20mm compact 16x2 line LCD that convinced David L. Jones that the uWatch project was actually doable with off-the-shelf components. If you are doing low-level programming of the uWatch, such as making "custom characters", you might want to look at the datasheet (via "Moon Phases").
Alas, that original display pulls about 2 mA, more power than anything else on the uWatch -- even the CPU uses less power (at 250 KHz). That's the main reason the current uWatch cannot run the display continuously (like a standard watch), but much be explicitly "turned on" every time you want to read the time.
The current uWatch2 rough draft seems likely to use the Newhaven NHD-C12832A1Z-FSW-FBW-3V3 128x32 Pixels display. Which uses less than 100uA which would enable a continuous display watch. The "white LED backlight" uses 30 mA at 3.0 V but is still very usable at much lower currents.
There's some discussion of some of the screens considered for the first iteration of the Open Source Watch at http://oswatch.org/details_screen.php .
Proposed displays: Limited to less than 10 mW of power when updating the time once a second (FIXME: reduce this limit and prune higher-power displays when this list gets too long): In no particular order:
- Newhaven NHD-C12832A1Z-FSW-FBW-3V3: 128x32 pixel display, white LED backlight, 41.4mm x 24.3mm (current top runner)
- Newhaven NHD-12864WX-T1TFH# Graphic LCD: 128x64 pixel display, white LED backlight, 38.0mm x 26.4mm. Power: 3.3 V at 0.18 mA typical (when 32 mA backlight is off)
- CFAX12864AP1 Graphic LCD: discontinued, apparently replaced by CFAX12864T1.
- CFAX12864T1-WFH Graphic LCD: 128x64 display with EL backlight. Power: 3.3 V at 0.18 mA typical; (the EL backlight version seems to require less power than the white LED backlight version; but how much power is that exactly?).
- CFAX12864T1-TFH Graphic LCD: 128x64 graphic LCD display with white LED backlight. Power: 3.3 V at 0.18 mA (when 3.5 V at 32 mA backlight is off)
- card display: 6 digit, 7 segment display module designed to fit inside a credit card. lightest-weight display of those on this list; adequate for 4-function calculator watch. Doesn't seem to show enough information for a scientific calculator.
- Sparkfun LCD displays: the color graphics LCD cell phone displays look relatively low power and are extremely well documented -- some of them are under $20.
- Graphic LCD 84x48 - Nokia 5110: power: the datasheet says 2.7 V to 3.3 V at 0.24 mA typical; but the "Graphic LCD Hookup Guide" tutorial says 2.7 to 3.3V at 7 mA (?) (when the 3 V at 100 mA white backlight LEDs are off) ... Adafruit: Nokia 5110/3310 Monochrome LCD tutorial
- Serial Miniature OLED Module - 1.5" (μOLED-128-G2-GFX) : 128 x 128 resolution, 65K colors, 1.5". Power: 5 V at 60 mA typical when on, 0.1 mA when all pixels black (?). Includes microSD socket.
- Serial Miniature LCD Module - 1.44" (uLCD-144-G2 GFX) : 128 x 128 resolution, 65K colors. Power: 5 V at 40 mA typical when on, 0.5 mA when all pixels black (?). Includes microSD socket.
- Basic 20x4 Character LCD - Black on Green 5V : Power: 5 V at 1.5 mA typical (when the 4 V at 250 mA LED backlight is off)
- SHARP Memory Display Breakout - Silver Monochrome (1.3", 96x96) : Power: 12 uW (?) 2.7 V to 3.3 V updated at 1 Hz. Apparently several libraries: U8glib: A graphics library with support for many different monochrome displays; ; ; ...
- Adafruit LCDs & displays has a huge list; a few of them are low-power enough for an always-on wristwatch display (have I missed any?):
- "SHARP Memory Display Breakout - 1.3" 96x96 Silver Monochrome" : Power: 12 uW (4 uA at 3.3 V with 1 Hz data refresh)
- Graphic ST7565 Positive LCD (128x64) with RGB backlight + extras - ST7565 : Power: 3.0 V at 1 mA (when the 5.0 V at 120 mA backlight is off) (What exactly is the difference between this and the "Graphic ST7565 Negative LCD (128x64) with RGB backlight + extras - ST7565"?)
- "RGB backlight positive LCD 16x2 + extras - black on RGB" and "RGB backlight negative LCD 16x2 + extras - RGB on black". Is this really 2.7 V to 4.5 V at 0.3 mA ? (When R, G, and B LEDs are turned off).
- Digikey has a long list of display modules at Digikey: LCD and OLED Character and Numeric Display Modules in stock and also Digikey: LCD and OLED Graphic Display Modules in stock. Which of them are low-power enough for an always-on wristwatch display?
- ... Have you seen a display that would work on a wrist calculator? Please add it to the list here! ...
Some threads discussing diplays: "Hardware Stuff » Why not a smaller LCD...",