Mike Harrison said:

>>1) If my external analog signal(-5V to 5V) is using a different power
>> supply, how shall I connect these 3 pins?
> If you only need a not-too accurate reading, a simple answer would be to
>  use a 5V reference, connect your input via 10K to the ADC pin, and add
> 10K betwen the adc pin and Vref (assuming source impedance of Vref is
> not too high) - this will convert your -5 to +5 input into the range
> 0..5V. As it's Friday afternoon I can't immediately think sufficiently
> well to say if this will be linear or not, but it may work for
> non-critical applications.

It will work fine, it's how the cheap data acquisition boards do it.
Values returned are linear, just multiply the value by 2 and subtract 5 to
know the applied voltage.

-Bob

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