PARTS AVAILABILITY
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Rauf, The internet should allow you easy access to worldwide electronic distributors. Its just a matter of currency exchange (which credit cards can handle) and then shipping costs.

ERRORS YOU'LL NEVER KNOW YOU HAVE
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No one brought up ratiometric vs other types of ADCs. Don't get me started. :)

I work in communications instrumentation and I take accuracy and computations extremely seriously in my product line. My advice on ADCs would probably be overkill for the project that initiated this topic. Most people in my opinion choose ADCs poorly but happily don't know it due to sloppy computations and measurement. If it looks right, that's often considered design validation. :)

I've known 30 Million dollar companies abort projects due to time wasted bumping around in this realm. (I might add, that I wasn't working for any of these troubled corporations.)

I agree with Peter and others that extenal ADCs are superior (by far) internal ADCs. If you want to do real measurement as opposed to hobbyist projects, you'll need a special layout area for your analog circuitry on the PCB board, well separated from the digital section. And need I say, attention has to be given to the power supply and distribution as voltage noise will often distort your ADC measurements.

EVEN EXPERTS GET ADCS SELECTION WRONG
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I once subcontracted an analog expert to select a ADC and his advice was all incorrect and clueless. This guy was very smart, but he didn't understand microprocessors at all and so he really had no idea what the ramifications were of selecting serial vs parallel or what bit resolutions a job required. I think his way was to build it and see what you get.

(I'm currently subcontracting with a THIRD analog engineer... getting good results from these guys have been my only everpresent corporate frustration.)

Luckily I didn't have to pay that guy a dime for his penny-advice due to scheduling problems. Instead I took it on myself and solved the design correctly. I used Microsoft Excel to model the computation rates required and the resolution needed and wrote some calculation routines for timing until I came up with the perfect attributes required of the ADC. National Semi made the best fit. It worked so beautifully in the lab that I hated dropping the circuitry when I had a innovative replacement idea that I won't discuss.

aka J