Go Down

Topic: DAC's output voltage managment on Arduino Due (Read 2824 times) previous topic - next topic

David_ZI

Hi everyone,


Currently setting up Arduino Due for a Lab project, and would like to get an advice. I need both DAC's on Due to be able to output a voltage from 0- max 4 Volts. Is there a chance that the Due will do it without any additional /and or support circuitry= ?, and second question, is the Due capable of using both onboard DAC'S simultaneously=?  :smiley-confuse:


David
programm is not Ready...

ard_newbie


I need both DAC's on Due to be able to output a voltage from 0- max 4 Volts. Is there a chance that the Due will do it without any additional /and or support circuitry= David
No, see this tutorial:

http://ardupiclab.blogspot.fr/2015/07/how-to-modify-analog-output-range-of.html

is the Due capable of using both onboard DAC'S simultaneously=?  
Yes, select both channels and Word transfer in DACC_MR with the appropriate channel setting (bits 12 and 28).

David_ZI

Hi, thanks for the article. I just want to use the Analog to Digital Chain on Arduino Due, that said, to read multiple analog signals and then output suitable response signal via the 2DACs. Let's say similar to PID controller. You think the board itself is capable of doing that, having restrictions on Hardware level?

programm is not Ready...

ard_newbie


David_ZI

so one has even several options to output voltage via AnalogWrite(), which means PWM, and of course the DACs, come into play, so i can easyily use both lets, say pwm and DAC;s in parralell? :smiley-surprise:
programm is not Ready...

ard_newbie

#5
Nov 07, 2017, 06:29 am Last Edit: Nov 07, 2017, 06:29 am by ard_newbie
You can use the PWM controller in parrallel with de DACs.

Note that the DACs output is a true analog voltage which is not the case of a PWM output. You will have to low-pass filter your PWM output to transform it into an analog voltage:

https://www.allaboutcircuits.com/technical-articles/low-pass-filter-a-pwm-signal-into-an-analog-voltage/

David_ZI


what is really not clear to me, how one can achieve make ADC sense smaller amounts of milivolts?? say if my ADC range is 0-4 Volts, then the minimum voltage it can sense is 4/4095=0.97miliVolts. I need to make this value something 0.5-0.3 miliVotls.

any ideas what could make that come ture= ? :smiley-confuse:

programm is not Ready...

ard_newbie

#7
Nov 08, 2017, 07:36 am Last Edit: Nov 08, 2017, 07:48 am by ard_newbie
You would need to transform the 12-bit DUE ADC to a virtual 13-bit ADC. The answer to this is oversampling, inputing white noise (dithering) and averaging.

http://www.atmel.com/images/doc8003.pdf

https://www.silabs.com/documents/public/application-notes/an118.pdf

Note that the DUE TRNG controller is able to produce a gaussian noise (white noise).

And be careful, the DUE is 3.3V compliant only.


David_ZI

great article newbie ! thank you so much... will try to do that...
programm is not Ready...

David_ZI

Hi newbie, currently trying to interface the thermocouple directly to analog pins, and just want to make sure i understand it right, the thermocouple plus + and minus- terminals should be connected to analog pins like one for Plus + and one for Minus- ? but in this case we do not short circuit the pins=?


 :smiley-confuse:
programm is not Ready...

weird_dave

What thermocouple are you using and what temperature range are you interested in? I suspect you are going to need to amplify the signal before you sample it, in reality you will do that anyway, incorporating some common mode noise rejection.

David_ZI

its N-P type thermopile. What i am very curious about, in most simple case, lets say where no OP amps or Instrumental amps or any other circuitry or IC is involved. Just we have plus and minus wires coming directly from thermopile. Is it technically correct to connect thermopile + to an analog pin, and thermopile - to another analog pin on controller?.
programm is not Ready...

weird_dave

Have you got a link to your sensor?

If I've read this correctly, you're suggesting connecting the +ve and -ve to 2 separate analogue reading pins, this is not technically correct, no. The -ve would connect to gnd on a Due. I don't know the specifics of your sensor, but I suspect it will require amplification to give you a reading (P-N thermopile doesn't mean much to me or google, hence the request for a link).

David_ZI

Hi wierd_dave, 

http://www.xensor.nl/pdffiles/sheets/nanogas3939.pdf

the one I'm using is XI-395/390. So al the circuitry is directly doped on the silicon membrane. I was thinking to get one of the MAX-31856 IC to lock it in between thermopile and Due. But beforehand, was curious if the Due itself will read out some data directly.


programm is not Ready...

weird_dave

Interesting device!

Using something like the Maxim part is a good idea as it has compensation and does the digital conversion for you. The AD595 may also be worth a look if you really want to use the Due ADCs.

Purely for initial testing purposes, you should be able to connect a digital multimeter and get a reading and then compare that to a reading using a Due, there may be some discrepancy as the Due's input impedance may be low enough to skew it noticeably (I haven't quite had time to understand that part of the SAM3X datasheet). The result is never going to be fantastic going straight to the Due inputs.

What temperature range are you looking at?

Go Up