The 10 bit A/D has 1 part in 1024 resolution. If you use a 2 volt
reference, the resolution will be only be about 2 mv.
There are a pile of external A/D converters you can use - I like the Maxim
products - the MAX187 is a 12 bit serial (SPI) A/D with a built-in 4.096
volt reference; there make other versions without the reference, so you can
supply your own. A 12 bit converter gives you 1 part in 4096. With a 2 volt
reference, that is 0.5 millivolt resolution. Other companies make similar
products - Linear Technology, National ... Not cheap though. Check their
web sites, then Digikey for prices. Some places (e.g. Maxim) will send you
samples.
Note that when working with analog stuff, layout, bypassing, and power
supply filtering are important - you are dealing with f**k-all voltages, as
an old professor used to say. Read the data sheets carefully - they usually
describe what needs to be done.
I've never done the bit-banging in ASM, since I use Picbasic most of the
time, but the protocol isn't difficult - the data sheets for the A/D will
show you all the timing diagrams. And someone here must have done the SPI
stuff.
As to output to the PC serial port, again. I'm sure there are people who
have serial I/O routines - I know there are Microchip App notes with serial
I/O routines.
Larry
At 07:09 AM 1/31/2003 -0800, you wrote:
{Quote hidden}>I want to read a DC voltage, .200 to 2.000 volts, into a PC serial port. I
>need .001volt resolution.
>
>I was thinking of the 16f676 with the 10 bit AD converter with a reference
>voltage set at about 2.000 volts.
>
>Would this provide the results I need or are there factors involved I am
>not aware of.
>
>It doesn't have any SPI, but would it be to difficult to bit bang the info
>out a port pin?
>
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Larry Bradley
Orleans (Ottawa), Ontario, CANADA
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