[sdiy] SOIC audio ADCs & dsPIC33F devices with codec interfaces not shown as such in the selector chart

[Robin Whittle]

For those unfamiliar with the dsPIC33F series, these microcontrollers
cost a few dollars and have a 40MIPS 16 bit CPU which can be used, with
care, to do a full multiply accumulate, with all fetching and storing,
pipelined so this occurs in a single instruction cycle.

A particularly interesting aspect of these it that some have a good (so
I believe, it has been mentioned on this list - I haven't used it yet)
sigma-delta stereo audio DAC on board and that some of these devices are
in 28 pin DIP packages.

They don't have matching audio ADCs - just conventional 12bit successive
approximation ADCs.  This raises a question of how we can connect an
external audio ADC.  This leads to the question of whether these devices
have a "Codec Interface" - a section which connects with a few wires and
the I2S protocol to an ADC, DAC or CODEC.  This section does DMA to
circular RAM buffers and interrupts so it can be used without much CPU
intervention.


I reported this problem to Microchip in May 2010 but never got a reply.
 The problem remains and I reported it to them at
webcorrections at microchip.com again today, requesting that they reply.

The selector chart at:

  http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=8192&mid=14

and the individual device webpages which are linked to from this are all
erroneous for the devices listed below, in that these devices DO HAVE a
"Codec Interface" AKA "Data Converter Interface" AKA DCI, which can be
used to connect to I2S interfaces on (typically) stereo audio
sigma-delta DACs, ADCs or Codecs (both DAC and ADC).  This can be
verified by looking "DCI" in the include files for each device which are
part of the MPLAB (not MPLAB-X . . . which I and other people have found
difficult to use).  This chart and the associated webpages indicate that
these chips DON'T have this interface.

These devices are all covered by the one datasheet:

  http://ww1.microchip.com/downloads/en/DeviceDoc/70292G.pdf

Here are the chips with a few pertinent details.  This will only look
good with a fixed width font.  The sizes for Program and Data RAM are
bytes, so divide by 2 to get 16 bit words.  For most of the devices, 2k
words can be used by DMA.

The DAC pins refers to the 16 bit sigma-delta stereo audio DAC which
some devices have.  Both the 4 and 6 pin options are fine for stereo.

                   Pins                  Prog  Data  DAC
dsPIC33FJ128GP804  44 QFN TQFP           128     16    6
dsPIC33FJ128GP802  28 SPDIP SOIC QFN-S   128     16    4

dsPIC33FJ128GP204  44 QFN TQFP           128      8    -
dsPIC33FJ128GP202  28 SPDIP SOIC QFN-S   128      8    -

 dsPIC33FJ64GP804  44 QFN TQFP            64     16    6
 dsPIC33FJ64GP802  28 SPDIP SOIC QFN-S    64     16    4

 dsPIC33FJ64GP204  44 QFN TQFP            64      8    -
 dsPIC33FJ64GP202  28 SPDIP SOIC QFN-S    64      8    -

 dsPIC33FJ32GP304  44 QFN TQFP            32      4    -
 dsPIC33FJ32GP302  28 SPDIP SOIC QFN-S    32      4    -


The 28 pin DIP devices are of particular interest since they can be used
without SMD heroics.

There's no such thing, as far as I know, as an I2C ADC or CODEC which is
in a DIP package.  SOIC is the only chip package which I think can be
hand-soldered without SMD heroics.  There are a few such ADCs:

  TI (ex Burr Brown) PCM1801:    5V SOIC 14 pins
  Wolfson WM8738:              3.3V SOIC 14 pins
  Wolfson WM8783:              3.3V SOIC  8 pins

The Wolfson devices are listed here:

  http://www.wolfsonmicro.com/products/adcs/

and are available at Mouser and/or Farnell/element14.  They are
inexpensive, such as, for the 8 pin WM8738, AUD$2.48 (Q 1 - 9) at
element14 (in stock) and at Mouser (not yet in stock) $1.12 (Q 100+)

I find it easy to hand solder an 8 pin SOIC.  I will be investigating
the WM8783 since the WM8738 has no obvious advantages over it.  As far
as I can tell, it should be straightforward to interface the WM8783 with
the dsPIC33FJ128GP802.

  - Robin