[oopic] Re: Digital Potentiometers

--- In oopic@yahoogroups.com, carson hoyt <carr6565@...> wrote:
>
> Thanks Richard that is exactly the kind of information I'm looking
for. Another thing, I'm really looking to use multiple digipots, if I
am making a lot of adjustments to the digipots is there going to be a
lag time since the connection is I2C? Also can I control the pots
individually on the I2C line if they are daisy chained together?
> Concerning resolution: I'm going to be using these pots in an audio
device. Should I be concerned about resolution. Right now I'm looking
at pots with 1000+ resolution but these are kind of expensive and not
available through my usual part supplier. I guess I'll just start
small and work my way. I really appreciate the help.
>
> Carson

There will be a way to have unique I2C addresses for quite a few
devices. At least 8 in the case of the Maxim MAX5477..MMAX5479.
Beyond that, things get complicated. Remember to divide the address
by 2 when using the OOPic. Why? Well, the least significant bit is
the R/W' bit and only the most significant 7 bits are address bits.

The lag time for an OOPic will vary because the OOPic has to read the
Basic code, interpret what needs to be done and then bit-bang the I2C
message. Then it starts on the next 'pot. I would expect 5 mS
between 'pot adjustments but that is just a wild guess. I have never
timed it. It could be much more...

If speed is your requirement, the OOPic isn't the way to get there.
The 'pots can handle a 400 kHz clock rate and, if each command takes 3
bytes, you would be looking at changing them at more than 10,000 times
a second. Or all 8 in about a mS! But that would be with a more
capable uC and coding in C.

Richard

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