reading analog signals on a MCU with only digital I/O

Joe:

The answer is "yes", such chips exist.  One of the easier
ways to find them is to use the parametric search capability
of DigiKey.  Go to <http://www.digikey.com/>  and type in
"A/D Converter".  Select the catagory with 8000+ items in it.
Now you have the parametric tables.  Narrow down your search
with I2C, SPI, and 3-wire, select some packages that you can
live with, etc.  Now comes sticker shock.

Once you have found a part number that you like, you can
go to <http://www.findchips.com/>  and see if somebody sells
it for a better prices.

A dedicated PIC/AVR with built in A/D is frequently
cheaper than most of these stand alone chips.  However,
there is the up front cost of getting a AVR/PIC programmer.

-Wayne

No kidding.  Those seem ridiculously expensive.  (For those following
along at home, the cheapest 8-pin DIP I could find in single quantities
was the AD7893ANZ-2-ND for $16.50.)


Sure, but this is the sort of thing where your friendly local robotics
club can help out.  I'm not all that familiar with these chips, though.  
Is there one you'd recommend that has at least, say, four A/D channels?

This also seems like the sort of thing where an industrious hobbyist
could make a few extra bucks, selling pre-programmed chips with friendly
instructions on how to use them.  At (say) $10 each, you could well
undercut the competition and still make a tidy profit per chip.

In fact, I'm surprised nobody's doing this... but maybe it doesn't come
up to often.  I take it that most MCU's have A/D channels built in?

Thanks,
- Joe

You need to look a little harder.  The ADC08831IN and the ADC08832IN
were about $2.51 quantity 1 (in stock).  There are plenty in
the $3-$4 range.

Make sure that you do not over constrain your search.  I usually
select package first and then select other features.

Getting the hang of Digikey parametric search takes a little
time and patience, but it is worth it in the end.


I'm from the PIC side of the fence.  I use the PIC16F688 for
everything.  I buy 'em in tubes of 25 from Mouser or Digikey.
I use 'em like popcorn.

I'll let somebody else chime in for the appropriate Atmel part
(probably and ATtiny##.)


Microcontrollers are cheaper, but there is not that much margin.
Most people will just find a MCU with A/D built in.


A/D conversion is the first thing most MCU vendors add to their
product mix.

-Wayne

Yes, I frequently end up not finding what I really wanted at DigiKey,
which is why it's great that I have kind folks like you to ask for help.  
:)  I'm not sure quite what I did wrong in this case...  pity that their
parametric search doesn't include "price" as a parameter!


:)  Well, I want to get to that point too.  Seems to me that they're the
swiss-army knife of electronics; once you learn to program and support
one of these things, you can use them in place of a whole lot of more
specialized parts.


Yes, if there are solutions in the $3-$4 range (or $9 for a 4-channel
one), then there isn't as much opportunity as I thought.


Yes, I wish I had one with A/D built in... but I really dig the
ARMexpress in every other way, which is why I'm putting a bit of effort
into seeing how this one little problem can be solved.


Yeah, Coridium did that with their newer ARMmite board, but they also
took a couple of big steps backwards IMHO (much larger form factor,
harder to prototype with as it's no longer a DIP package, programmable
only from the built-in USB port rather than serial, and requires the use
of Windows).

Thanks,
- Joe

[snip]


I just wish they would stop showing me items that have 1000
piece minimum orders!


That's the way I treat them.  One of my projects had 9
PIC's on it.

[snip money making opportunity]


The ARMmite does sound like they removed some pertty interesting
features.

I've always been scratching my head about the ARM's.  Billions
of them are made, but why can't some clever manufacturer figure
out how to put one into a DIP package for less then $10?

-Wayne