Actually, a friend of mine and I are working on almost exactly this project.
It started with a F91-W, but we found out that the display is somewhat 'crippled'. Casio was very clever at saving segments, so they paralled some segments. For example, they connected the A and D segment of 10 minute digit.
To interface the LCD, you need a microcontroller with a builtin LCD controller since the LCD panel is a 'bare glass' one without any sort of electronics. We planned to use an MSP430F417. We got the PCB layout almost finished, but then decided that it'd be not worth it, considering that the display is that limited.
So we bough a Casio W800 with a much bigger LCD. Unfortunately, the LCD is configured as 5 COMs by 27 segments, so you need MCU with an LCD controller that can drive 5 coms and is available in a QFN64 package. QFN is pretty much the only option you've got, since TQFP is way too large and when these MCUs have BGA packages, they only come with minuscule ball pitch. After searching all common and obscure MCU manufacturers there are only two MCU families left that can drive this LCD: Some PIC24 and some Renesas RL78. We went for the RL78 since they've got better compiler support (supported by GCC, not some obscure proprietary compiler). Right now, I'm evaluating whether the LCD controller of the RL78 can drive the W800 LCD, since the LCD controller only supports 4 MUX and 8 MUX. For this purpose, we made a PCB to interface the bare LCD to an RL78 eval board. See also my thread on renesasrulz:
http://renesasrulz.com/renesas_forum_home/rl78/f/26/t/5850.aspxPlanned peripherals to include:
- nRF24L01 2.4GHz radio
- Compass, maybe accelerometer
The reason for doing all this is that the wrist strap of my ez430 Chronos is disintegrating and I really want to have a somewhat 'smart' watch that runs on a coin cell for a year and doesn't need to be recharged every year.