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.
0 to 5 volt ADC
Author
Message
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
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.
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
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.
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
How about an analog mux and one divider. That gives you "exactly" the same factor on all channels.
Jim
ka7ehk wrote:
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.
How about an analog mux and one divider. That gives you "exactly" the same factor on all channels.Jim
Cheers,
Ross
16 channel muxes exist though.
indianajones11 wrote:
Do you have a recommendation?
16 channel muxes exist though.
Max396, max. Ron = 100 ohms :cry: , matched w/in 6 ohms. But they have others.
indianajones11 wrote:
Thanks.
Max396, max. Ron = 100 ohms :cry: , matched w/in 6 ohms. But they have others.
Level: Hangaround
Joined: Thu. May 27, 2010
Posts: 488 View posts
Location: The land of Cyrus the Great
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.
I thought the ADC max was 3.3-0.6 = 2.7V?
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)
hi, .1% resistors are cheap, < penny.
Level: 10k+ Postman
Joined: Fri. Jul 1, 2005
Posts: 13672 View posts
Location: Basingstoke, Hampshire, UK
Really - are you sure?
(and are you adjusting that for 2011 prices?)
Level: Moderator
Joined: Mon. Jul 18, 2005
Posts: 90743 View posts
Location: (using avr-gcc in) Finchingfield, Essex, England
