> sounds good
> I'd rather like a DDL that can be reprogrammed from SW than
> an analog that you need to change parts. But neither is easy, of course.

Only the signal conditioning are analog, the software makes all the
decisions.

> It seems to me that the AC resistance-measurement can be done with
>  a PWM channel, RC, amplification and an (optional rectifying and
> lowpass and)
>  AD input. (maybe the first RC is not needed at all, squarewave would suit
>  well for AC resistance measurement).

There is no need to use a PWM channel for the Ri measurement, an OP astable
oscillator is better suited because of the +-15volts swing. The high voltage
is the best way to regulate the current, I use an integrated DC-DC converter
for 10euro to create this current. Don't worry, it is available everywhere.
(This is also a reason to keep EGT and WB on the same board)

The route is: Square wave - series capacitor - nearst cell - buffer
(precision)- RC (HP) - amplification (precision) - 8th order hp -
rectifier - LP - ADC.

If we could implement the 8th order filter and the parts following it in
software it would be great. But I think that we need a few more mips for the
filter;)

It may be possible to trace the resistance of the nearst cell with a voltage
divider arrangement. I making some calculations right now.

> > MS-AVR board when the duplicate components are removed. Let me
> know if you
> > find an integrated high order hipass filter!
>
> what freq? 5th order?

Around 1000-2000Hz is fine, 5th order will probably do the trick but the
current design is 8th order. I have found several lp filters but no hp.

> > space, this is with common hole mount components. The circuit could be
> > called a digital diy-wb circuit
>
> Are there patent issues?

It is based on my LSU design and is not related to the diy-wb in any way.
But it will give the same functionallity as the diy-wb would if it weren't a
poor design. Except for the linear output of course. I had planed to release
this design under the diy-eula with the exception that I and anyone that buy
the manufacturing right from me can sell it for a profit. I just don't want
to see this design in the hands of Techedge without making a buck. If I
release it I will be ready to provide a parts kit and boards with a markup
of around 10-15euro. In other words, the 'Minimal Digital diy-wb.zip' file
you recived are under copyright for the time being, it was also made late
one night and haven't been tested or even checked after that.

