WEIGHT WATCHER DIGITAL SCALE (WWDS)

((I am an electrical engineering student)):

ABSTRACT:

weight watcher digital scale (WWDS) is a digital scale that provides multiple users with unique data logs and conveyes weight fluctuation with respect to time. weight is measured with a resistive pressure tranducer and a linear amplifier circuit. use information is communicated via a keypad and decoder unit. Time is maintained with a real time clock, and data stored at nonvolatile memory; both components serially over a common I2C bus. All information, such as prompts, weight and time, are conveyed to the user with an LCD. The activity of these separate components is cordinated with a microcontroller, which includes an A/D analog-to-digital converter for the weight signal.

this is my project.........

i choosed AT89s8252 and i bult the circuit including (AT89s8252, 4X4 keypad and 16X2 LCD) and I made the code >>>>>no problem here.

but my qustions;

1- was it a correct decision to chose AT89s8252?

2- if i do not want to use EEPROM to store the 10 user's data (passwords+height+last weight), what will be your opinion if i use the familiar RAM memory that built in my 8252 and the 8252 will be powered by a backup power supply becuse i do not want these data to be lost.

3- what about the TIME?

see what my doctor said to me:

Register/clock is an IC consists of registers decicated to maintaing time. additionally, it requiers its own crystal oscillator. Optionally, it can be powered by a backup power supply to maintain time in the event that power is removed from the main circuit.

but doctor gave me all design options.. i can do what i want to reach the goal.

but my idea is to use the the softwared RCT using the 8252 crustal itself>>>>>is it good idea? what about the problem of approximation? i reed that with every mov instruction, this will take 2 cylcle ((as i remember)) which will make the big error after long time because the 8252 will be powered forever?

which choice you say?

4- last point: the digital scale:

read this:
(((microcontroller, which includes an A/D analog-to-digital converter for the weight signal.)))

does my chip provide A/D converter?
if yes how to use it?

not that i can use ready scale. but how to connect it to the 8252 and if there are companies provide a special scale for my project.