You have a few options outside your chosen solution, most of which can
be explored via this google search:
http://www.google.com/search?q=digital+gain+control

First, you might look at amplifiers with built int digital gain
control, such as these Linear Technology parts:
http://www.linear.com/pc/viewCategory.jsp?navId=H0,C1,C1154,C1009,C1121
If the link doesn't work, navigate to
Home  >  Products  >  Signal Conditioning  >  Operational Amplifiers
(Op Amps)  >  Programmable Gain Amplifiers

Second, you might look into CMOS digital switches - some have a 20v range:
http://schematics.blogspot.com/2005/01/digital-gain-control-of-opamp.html

Of course, if you really want to kludge something together, tie a
servo to a pot...  ;-D

Good luck!

-Adam

On 5/8/08, Martin <martin@nnytech.net> wrote:
> I have an analog circuit that has a (normally) negative polarity DC
> feedback signal. I'd like to change the gain of the circuit digitally,
> so I'd like to use a digital pot. The problem is that a digital pot can
> only take signals between VEE and VDD - most usually probably 0v to 5v.
>
> My rails are +5/0/-5 and my feedback lies somewhere between 0 and -5.
> Has anyone encountered a digital pot that can either take a 10v supply,
> or has level shifters on the digital lines? I think I might be able to
> use a CD4052 with discrete resistors, but then it's a 16 pin chip I have
> to put on the board.
>
> Any ideas?
>
> -
> Martin
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