On Mon, 02 May 2005 22:19:04 -0700, Bob Cain
wrote:



Pooh Bear wrote:

...

What I would do is to use a simple microcontroller ( I prefer the 8031
family myself ) and use a rotary encoder - as opposed to a pot - to adjust
gain. Would be dead easy to include a readout of gain on a couple of 7
segment displays too.

I like it! I was just looking at the dsPIC but that's
overkill even tho they're cheap. It would be nice, however,

This app is in the 'any micro can do it' category, I'd use whatever
you're most familiar with.

to have some reserve capability and bond with what looks to
be a very interesting part. I assume the 8031 could
generate the required select and serial control stream to
the PGA2500 without any jelly beans.

I have no doubt you can directly connect them and bit-bang the
pins.

Are shaft encoders Gray code or base 2? OST, the 8031 could
do away with any possible intermediate states that would
cause glitches.

ISTR you can get whatever encoding you want, but the one I've used
is Gray code (quadrature outputs). I did debouncing on a cheap ($1 at
digikey) mechanical-switch quadrature rotary encoder, details he

http://groups-beta.google.com/group/...e12cc30c273ff8

An optical-interface encoder will have (IMHO) a better feel, but
they cost a LOT more, like $10 to $20 and more. Those must be for the
Logic Analyzer front-panel market, as essentially the same hardware in
a $5 (older mechanical design) computer mouse.

You might also have a microcontroller that includes
program-writable FLASH or add some small serial EEPROM, and have the
level saved and the processor shut down/go to wait mode (the encoder
can conveniently be wired to give a wake-up interrupt when turned)
after about a second of encoder non-activity. Then this level can be
recalled at power-up, and it acts just like a hardware switch that
keeps its gain value through power down.

In my other post in this thread I wrote about a potentiometer and
A/D/microcontroller, because I thought your "rotary switched
resistors" disclaimer meant you wanted something analog, or at least
looked and felt line a single analog (continuous change) control. This
will definitely be a discrete-change "digital" solution.

Bob

-----
http://mindspring.com/~benbradley

Bob Cain wrote:

Pooh Bear wrote:

Bob Cain wrote:


Pooh Bear wrote:


If you can live with 1dB steps TI's PGA2500. Rather a good mic amp in
its own right. Gain is controlled by an SPI interface.

_Very_ nice part, thanks. I'd like to control it with a
pot, though, and that will take a little thought. Maybe
there's a PIC that can do the job with a single chip.

Definitely a go-to part for a pre/ADC.


What I would do is to use a simple microcontroller ( I prefer the 8031
family myself ) and use a rotary encoder - as opposed to a pot - to adjust
gain. Would be dead easy to include a readout of gain on a couple of 7
segment displays too.

I like it! I was just looking at the dsPIC but that's
overkill even tho they're cheap. It would be nice, however,
to have some reserve capability and bond with what looks to
be a very interesting part. I assume the 8031 could
generate the required select and serial control stream to
the PGA2500 without any jelly beans.

Absolutely. The only bits you'd need are a few pull up Rs and the like.
Everything including the LED drivers would fit into an 87C51 ( internal Eprom )
nicely.

Are shaft encoders Gray code or base 2? OST, the 8031 could
do away with any possible intermediate states that would
cause glitches.

The encoders I'm familar with ( the cheap and cheerful consumer types ) have
'quadrature' outputs.

You hook one of them up to a hardware interrupt line and the interrupt reads 0
or 1 on the other output which means clockwise / counterclockwise. You need to
be careful about contact bounce of course.

It would make sense also to have a tiny serial EEprom to store gain data so that
the unit powers up with the same gain in effect as when it was powered off.

Graham

Very simple, been doing it for years, in a variety of formats including
PIC and 80x1 implementations.

The TI should do a reasonable job, but it looks like it's sort of
strangled by noise, or at least that's what I see in those graphs of
gain vs noise. Not front end noise, but digital noise getting
into the system.

I know you can do better, but not easier. It'll sound like an SSM-2017
or any other variation of hybrid instrumentation amp done passably well.

Clean, edgy, gutless, and lifeless.






Pooh Bear wrote:
Bob Cain wrote:


Pooh Bear wrote:

Bob Cain wrote:



Pooh Bear wrote:



If you can live with 1dB steps TI's PGA2500. Rather a good mic amp in
its own right. Gain is controlled by an SPI interface.

_Very_ nice part, thanks. I'd like to control it with a
pot, though, and that will take a little thought. Maybe
there's a PIC that can do the job with a single chip.

Definitely a go-to part for a pre/ADC.


What I would do is to use a simple microcontroller ( I prefer the 8031
family myself ) and use a rotary encoder - as opposed to a pot - to adjust
gain. Would be dead easy to include a readout of gain on a couple of 7
segment displays too.

I like it! I was just looking at the dsPIC but that's
overkill even tho they're cheap. It would be nice, however,
to have some reserve capability and bond with what looks to
be a very interesting part. I assume the 8031 could
generate the required select and serial control stream to
the PGA2500 without any jelly beans.


Absolutely. The only bits you'd need are a few pull up Rs and the like.
Everything including the LED drivers would fit into an 87C51 ( internal Eprom )
nicely.


Are shaft encoders Gray code or base 2? OST, the 8031 could
do away with any possible intermediate states that would
cause glitches.


The encoders I'm familar with ( the cheap and cheerful consumer types ) have
'quadrature' outputs.

You hook one of them up to a hardware interrupt line and the interrupt reads 0
or 1 on the other output which means clockwise / counterclockwise. You need to
be careful about contact bounce of course.

It would make sense also to have a tiny serial EEprom to store gain data so that
the unit powers up with the same gain in effect as when it was powered off.

Graham

Ben Bradley wrote:

Are shaft encoders Gray code or base 2? OST, the 8031 could
do away with any possible intermediate states that would
cause glitches.


ISTR you can get whatever encoding you want, but the one I've used
is Gray code (quadrature outputs). I did debouncing on a cheap ($1 at
digikey) mechanical-switch quadrature rotary encoder, details he

http://groups-beta.google.com/group/...e12cc30c273ff8


Thanks!

You might also have a microcontroller that includes
program-writable FLASH or add some small serial EEPROM, and have the
level saved and the processor shut down/go to wait mode (the encoder
can conveniently be wired to give a wake-up interrupt when turned)
after about a second of encoder non-activity. Then this level can be
recalled at power-up, and it acts just like a hardware switch that
keeps its gain value through power down.

Yes, that would be pretty much mandatory.


In my other post in this thread I wrote about a potentiometer and
A/D/microcontroller, because I thought your "rotary switched
resistors" disclaimer meant you wanted something analog, or at least
looked and felt line a single analog (continuous change) control. This
will definitely be a discrete-change "digital" solution.

Yeah, I had thought that parts with digital control would be
too much of a pain in the ass to design with but I'm
rethinking that. I have a space constraint that rules
against the resistor/rotary-switch solution as well as a
cost of assembly consideration.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

Dan Kennedy wrote:

Very simple, been doing it for years, in a variety of formats including
PIC and 80x1 implementations.

The TI should do a reasonable job, but it looks like it's sort of
strangled by noise, or at least that's what I see in those graphs of
gain vs noise. Not front end noise, but digital noise getting
into the system.

Really ? How did you come to that conslusion ?

I have a PGA2500 EV board currently so I'll be making some checks soon anyway.

I know you can do better, but not easier. It'll sound like an SSM-2017
or any other variation of hybrid instrumentation amp done passably well.

Clean, edgy, gutless, and lifeless.

What would you suggest for added 'life and guts' ?


Graham

Dan Kennedy wrote:

Clean, edgy, gutless, and lifeless.

Yeah, probably true of any amplicator where the output is
only a scaled version of the input. :-)

(Amplicator is a word that just was coined in comp.dsp by
someone that isn't a native English speaker. I just love
the word for what it implies!)


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein