Re: The continuing saga of the hyperbolic tangent

John Popelish wrote...
>
> Mike Monett wrote:
>> Winfield Hill wrote:
>>> John Popelish wrote...
>>>
>>>> So I am trying to come up with a way to make best use of a limited
>>>> resolution converter, as a learning experience. I may well throw
>>>> the whole thing over after a bit of play and use a 16 bit converter.
>>>
>>> With 24-bit converters becoming commonplace, and selling for under
>>> $10 to the big boys, why fool around with 16 bits, let alone 10?
>>
>> The AD7791 claims 22 effective bits for $3.83/1k, with a very simple
>> serial interface. They allow two free samples:
>>
>> http://www.analog.com/en/prod/0%2C2877%2CAD7791%2C00.html
>>
>> The TI ADS1271 is $5.90/1k, offers high sample rate, three operating
>> modes, and a serial interface that can be daisy-chained. Also free
>> samples:
>>
>> http://focus.ti.com/docs/prod/folders/print/ads1271.html

I'll see your cheap-ass AD7791, ADS1271 converters, and raise you
an industry-standard high-performance AKM ak5394A or Cirrus Logic
cs5381 multi-bit delta-sigma 192kHz 24-bit two-channel converter,
the latter only $18.80 single-pieces at Newark. Or, if you insist
on cheap, cheap, go with the remnants of the older Crystal cs5360
24-bit 48kHz 2-channel converters, in stock at Newark, $8.68 each.
Or the tiny 8-pin 24-bit cs5333-BZ, $8.91. If cost is foremost,
try cs5340 24-bit "karaoke A/D" - factory-priced at $1.92 qty 10k.

These little high-performance A/Ds are amazing. For example, if
you want to make a small super-simple one-channel machine, try the
8-pin cs5511, $4.36 ea at Newark, $2.93 qty 1k (Cirrus Logic has
the data***). This fellow consumes a miserly 1.9mW and spews a
20-bit data stream at clock/612, e.g., 200Hz with a 122kHz clock.
Sheesh, forget 10-bit converters and an LM13700. :>)

> You guys are trying to take all the fun out of this project.

Your hardware project makes little sense to me, much as I liked
the good old OPAs, Gilbert-cell variants, etc. Now, it would be
interesting to take a clever high-performance 3-axis sensor with
signal conditioning plus cheap 3-channel 24-bit converters, and
add a digital tanh signal post-processing step to reduce the raw
long-term data-archiving requirements. 200 3-axis Sa/s = 18.6GSa/yr
= 75GB/yr = 750GB/decade of 32-bit words, not including time stamping
and engineering data. You could find clever algorithms to reduce
that burden significantly. And to analyze and display data.


--
Thanks,
- Win
.

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