On Tue, Jul 19, 2011 at 2:20 AM, Bob Carpenter. <rgc3679 / yahoo.com> wrote:
>
> It's not clear whether you guys think a software ADC is impractical or
> whether it's impossible.

It's not impossible. It's just so very impractical that it might as well be=
.

> If you're saying it's impractical, is it due to performance - takes too
> long to convert analog voltages to digital values?

Yes.

> If it's impossible, is it because reading voltages at USB pins cannot be
> done in software?

That, too, more or less.

The third problem is that USB isn't even capable of *reading*
different voltages, much less a waveform! It can read an on state and
an off state. Analog signals are "composites" of different wave
lengths--you have electrical power as carrier wave, on top of which
you modulate all your other waves carrying actual data--which a
digital connection just can't handle (after all, that's what ADC/DAC
chips are for ;).

> I have not found any reasonably priced digital cameras - reasonable
> being in the range of $50/unit for quantities of 100. Please let me know
> if you have seen any.

If the problem is digitizing the video signal:

Get or build a DVR, and pull the already-encoded video from that. It's
cheaper and less headache-y that way. You'll probably need that
anyway, since CCTV usually means "surveillance", and *that* again
means "recording evidence for the police / court".

--=20
Phillip Gawlowski

phgaw.posterous.com | twitter.com/phgaw | gplus.to/phgaw

A method of solution is perfect if we can forsee from the start,
and even prove, that following that method we shall attain our aim.
=A0 =A0 =A0 =A0 =A0 =A0 =A0 -- Leibniz