Select AVR8 with 4 diff. ADC pairs and USART

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I'd think I've seen as many AVR8 models as nearly anyone.  But this one has me stumped.

 

A redesign of sorts is needed on one of our industrial control modules, as there appears to be cross-talk between channels.  Each channel has sensor excitation and return value that goes into the AVR8 ADC.

 

The redesign will isolate the excitation of each of the four channels.  To "isolate" the returned signal we want to use differential ADC pairs for each channel.

 

What AVR8 model has four distinct differential ADC channel pairs, plus four single-ended?  Tiny861A family has that but more on that later...

 

A complication is that the module communicates to the master via RS485 and MPCM/9-bit.  The Tiny861A has the USI, but no 9-bit provisions.  Tiny1634 has USART(s), but no differential.  Current design is Mega164--that has differential but only two distinct pairs.

 

Any suggestions? (product selector is useless for this...been there)

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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324 seems to have 2 sets of 4... neg a/d can be 1 or 2, pos can be 012345, 2 uarts and 9 bit. We use this one in the boost egt gauge (Mcnally Electronics)

 

Imagecraft compiler user

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Maybe you will need to plunge into the dreaded Xmegas sad

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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John beat me to it...

 

The Xmega32E5 is the "Tiny" of the Xmega lineup.

 

It has a 12-bit ADC, with 8 differential inputs.

 

For single ended inputs I think you set the negative terminal to one of several internal voltages, including Ground, via the register setup.

(I just did this recently and I've already forgotten the details)

 

Perhaps of interest is the internal gain option, as well.

 

Unlike the Xmega A series, the E series has the slower 300 KSamples/Sec sample rate.

 

The USART supports 9-bits, (although I've not tried that).

 

I used one differential and one single ended input in my recent EKG Project with good results.

 

JC

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DocJC wrote:
John beat me to it... The Xmega32E5 is the "Tiny" of the Xmega lineup. ...

 

Perhaps.  I'd rather not throw 5V=>3V into the modifications, but in the end we may indeed need to nearly "start over".

 

Right now the hardware guys are working on prototyping the isolation to ensure that it addresses the issue we are seeing.  If it does, then I'll move on to micro selection.

 

bobgardner wrote:
324 seems to have 2 sets of 4... neg a/d can be 1 or 2, pos can be 012345,

 

Many AVR8 models have that setup.  But I want/need four separate differential pairs.  As you said, most models only have two.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Tiny441 family fits my criteria.  [wow, a pretty nice chip for a buck and change.  REal USART; real SPI; relocatable pins; ...]  Perhaps not enough pins to do all four channels with one micro, but no biggie...

 

...but not enough pins for the needed ADC work plus a few more for the app.

 

Direction now is twin Mega164 with two differential pairs each.

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Wed. Apr 20, 2016 - 03:21 PM
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An absolute overkill the ATmega640/1280/2560??

 

10-bit Resolution
1 LSB Integral Non-linearity
± 2 LSB Absolute Accuracy
13 - 260 µs Conversion Time
Up to 76.9 kSPS (Up to 15 kSPS at Maximum Resolution)

 

*****************
16 Multiplexed Single Ended Input Channels
14 Differential input channels
4 Differential Input Channels with Optional Gain of 10x and 200x

*****************

Optional Left Adjustment for ADC Result Readout
0 - VCC ADC Input Voltage Range
2.7 - VCC Differential ADC Voltage Range
Selectable 2.56V or 1.1V ADC Reference Voltage
Free Running or Single Conversion Mode
Interrupt on ADC Conversion Complete
Sleep Mode Noise Canceler

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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js wrote:
An absolute overkill the ATmega640/1280/2560??

lol -- and I use that series. ;)  I don't think I scrolled down far enough to see the second "bank" of x1 differential channels.

 

Lessee-- Say ~$9 for '640.  2x Mega164A => ~$8.  But it isn't particularly cost-sensitive, and would be simpler in the app to not have two "half-modules".

 

Thanks.

 

...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Thu. Apr 21, 2016 - 01:12 PM