0 to 5 volt ADC

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Can the Xmega directly read 0-5volts on the ADC pins. What do you use for reference. Internal 1 volt, 1.6 volt or 5 volt on the AREF pins.

Think generously about people who know less than you about code. Don't think they should understand some technical concept. They don't, and they're not stupid for not understanding.

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Quote:
Can the Xmega directly read 0-5volts on the ADC pins

No.

The Xmegas run on 3 or 3.3 V Max, (3.6 V Absolute Maximum Rating, which is not where you run the chip...).

The maximum voltage on any pin is Vcc + 0.5V. But one ought to keep it < Vcc, (i.e. < 3 V).

However, Errata Rev H Xmega A1 says that the ADC output stage is limited to a max of 2.4 V.

Hence scale your input to keep the max <= 2.4 V and you should be OK.

Use the SEARCH option on this forum for other threads discussing the Xmega's ADC.

JC

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So I have to use voltage dividers ?. Do you know if there is some other way to do this then using a bunch of resitors.

Think generously about people who know less than you about code. Don't think they should understand some technical concept. They don't, and they're not stupid for not understanding.

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There is nothing simpler or less expensive than two resistors.

You could replace the lower resistor with a POT to adjust the attenuation factor, if that would be better for you.

You could use a Mega, (NOT an Xmega), running on 5 V, and use a 0-5 V input.

JC

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Quote:
There is nothing simpler or less expensive than two resistors

The problem is I use 10 ADC channels and they all have to be the same. Accurate resistors are very expensive.

Think generously about people who know less than you about code. Don't think they should understand some technical concept. They don't, and they're not stupid for not understanding.

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How many are you building?

If you want accuracy, and uniformity across the channels, then you have to pay the price for that.

You can do calibrations in hardware or software.

JC

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How about an analog mux and one divider. That gives you "exactly" the same factor on all channels.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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ka7ehk wrote:
How about an analog mux and one divider. That gives you "exactly" the same factor on all channels.

Jim

Providing all of the Rons of the MUX are closely matched and track with temperature. I am not aware of a 10 channel mux in a single package.

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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16 channel muxes exist though.

1) Studio 4.18 build 716 (SP3)
2) WinAvr 20100110
3) PN, all on Doze XP... For Now
A) Avr Dragon ver. 1
B) Avr MKII ISP, 2009 model
C) MKII JTAGICE ver. 1

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indianajones11 wrote:
16 channel muxes exist though.
Do you have a recommendation?

Ross McKenzie ValuSoft Melbourne Australia

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Max396, max. Ron = 100 ohms :cry: , matched w/in 6 ohms. But they have others.

1) Studio 4.18 build 716 (SP3)
2) WinAvr 20100110
3) PN, all on Doze XP... For Now
A) Avr Dragon ver. 1
B) Avr MKII ISP, 2009 model
C) MKII JTAGICE ver. 1

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indianajones11 wrote:
Max396, max. Ron = 100 ohms :cry: , matched w/in 6 ohms. But they have others.
Thanks.

Ross McKenzie ValuSoft Melbourne Australia

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DocJC wrote:

However, Errata Rev H Xmega A1 says that the ADC output stage is limited to a max of 2.4 V.

This is true only when using gain stage.

Ozhan KD
Knowledge is POWER

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I thought the ADC max was 3.3-0.6 = 2.7V?

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indianajones11 wrote:
Max396, max. Ron = 100 ohms :cry: , matched w/in 6 ohms. But they have others.

but it looks to cost more than the Xmega ?!

If the OP really needs 5V analog, then perhaps a dedicated ADC, or even a small uC as ADC would make more sense.

eg C8051F531A is 16 Chans of 5V.12b ADC for ~$2.50
or the
MAX11604EEE is 12 Chans of 5V 12b.ADC for a very similar price.
or, the Freescale HCS12 family, show 1.8-5V Vcc, with 12bADC for sub $3

This shows how small uC are displacing ADCs, and I see the MSP430AFExxx are another example of a remarkably cheap high resolution ADC, with a 'free' uC. (tho not 5V/10 chans)

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hi, .1% resistors are cheap, < penny.

<p>Vern</p>

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Really - are you sure?

 

(and are you adjusting that for 2011 prices?)

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Do you think they care after 7 years?