> From: Robert Zeff <rzeff@AINET.COM>
 > Subject:      Digital pot / attenuators?
 > To: PICLIST@MITVMA.MIT.EDU
 >
 > Hi,
 > I need to attenuate an audio signal.  I need something like
 > the AD7112 LogDac, but it's a bit pricey ($>10.00 and
 > requires lots of I/O lines.


What about using AD8402 (8403) 2/4 channel digital pot ?
It's price $2.5 for 2ch (8402) and $4.8 for 4ch (8403).
This devices needs only 3 wire SPI ( SDI,SCLK, CS) for
operation and have reset and shutdown inputs.
Pot's nominal is 10k,50k or 100k.

 >   I need to handle signal swings of +/- 10 volts.

Hm, AD8402/3 limited only 0-VDD (max 5.5V), but with OP its
possible to built +/-10v input schematics.

 > The Dallas parts are neat (I2C) but they
 > only handle 0 - 3 volts. Also, I need at least .5 db
 > steps, say 0 to -80dB. Any suggestions?

AD8402/03 have only 8bit (256 steps)= 46dB (as I remember),
but you may cascading both 2ch of 8402 (using double OP).

Some data from AD8402 datasheet :
--------------------------------------------------
  Bandwith (-3bB)                    600 kHz
  Total Harmonic Distortion (1kHz)   0.003 %
  Setting Time                       25 uS
  Resistor Voltage Noise             9 nV/Hz^-1
  Crosstalk                          -65 dB
  Power Supply Range                 2.7-5.5 V
---------------------------------------------------

I use AD8402 in my new production PIC programmer to
control VDD & VPP, very wonderful chip !

   Best Wishes, Alex Torres.
   Kharkov, Ukraine, exUSSR.
   E-Mail To : altor@cook.kharkov.ua   via InterNet
               or 2:461/28             via FidoNet

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