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Thread: What is a Sigma-Delta AtoD converter? [EE]
face BY : Alice Campbell email (remove spam text)

Guilty Party Replies:

Ha!! It's all true, what Scott says.  Spent about 3 weeks
getting the silly thing to work, it finally worked sunday at
about noon.  And i still have 1 hair left.

Last thursday, Scott told me that i might have an impedance
problem, and suggested a cap beneath the pot to match
impedance.  Didnt work.  But it gave me an idea, so i dropped
the pot like a hot potato and put in a cheesy old lm358 from
the junk pile.  Fearing to fry my new pin photodiode, i put
in a reverse-biased led and 4M of feedback and VOILA! it
works.  AND i used tris on the ports, both on 16F84 and

And try as i might, a pot just doesnt seem to work well in
this circuit.  When i get a chance, i will investigate
further, but i have not been successful in getting it to read
a pot.  It really likes to work with an opamp.  I agree that
the r-c constant for the main A2D is important, but it's more
important that any stabilizing cap on the output of the opamp
be a couple of orders of magnitude bigger than the one used
by the ADC.  The software can handle down to .01 uF caps at 4
MHz, but i wouldnt try such a small cap at 32kHz--well, maybe
i might try it later, just to confirm suspicion.  And i used
a mylar film cap for the A2D, no way after all that work will
i use leaky old caps.



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Subject (change) What is a Sigma-Delta AtoD converter? [EE]

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