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Topic: Arduino DUE - dac range (Read 411 times) previous topic - next topic

dimare_gabriele

Hello everybody

I'm using the DAC of arduino DUE to have a variable voltage to be converted into 0-20 mA .. (using the ad694)

but it accepts the input voltage 0-2.5 V .. Arduino DUE dac has 0.55V - 2,75V  range ..

is possible to adjust the tension ?

how do I fix ?

sorry for my English

James C4S

Don't output the maximum value.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

thatcadguy

Hi, I just asked a similar question about voltage to current conversion with the DAC here: http://forum.arduino.cc/index.php?topic=337053.0
Might be helpful.

dimare_gabriele

The problem si the minim value! 0,55 V

thatcadguy

Hi, looking at http://www.analog.com/media/en/technical-documentation/data-sheets/AD694.pdf

Another problem you might have is that it looks like it takes either 0-2 or 0-10 V, not 0-2.5V. But again, as James said, simply do not output the maximum value from the Due. As far as the minimum value goes, it looks like you can adjust the input buffer (look at pins 15 & 16, there is an ADJ and Voffset). Maybe someone more knowledgeable can explain further, but I think that's what you are looking for.

RayLivingston

If you need a current output, you're pretty much going to need an external op-amp to do voltage-to-current conversion.  That same op-amp can compensate for the goofy offset and range of the Due DAC, as well as scaling the output to give the range you want.  You won't get a passive circuit to give you what you need.

Regards,
Ray L.

James C4S

The problem si the minim value! 0,55 V
I did not notice before. My Due does the same.

You would probably need to build a buffer (maybe using an op-amp) to offset the signal back to 0V.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

dimare_gabriele

Hi, looking at http://www.analog.com/media/en/technical-documentation/data-sheets/AD694.pdf

Another problem you might have is that it looks like it takes either 0-2 or 0-10 V, not 0-2.5V. But again, as James said, simply do not output the maximum value from the Due. As far as the minimum value goes, it looks like you can adjust the input buffer (look at pins 15 & 16, there is an ADJ and Voffset). Maybe someone more knowledgeable can explain further, but I think that's what you are looking for.
On datasheet is written that for output 0-20mA need a input range of 0-2.5V .. or not?

( page 5 of the datasheet , table top right )


If you need a current output, you're pretty much going to need an external op-amp to do voltage-to-current conversion.  That same op-amp can compensate for the goofy offset and range of the Due DAC, as well as scaling the output to give the range you want.  You won't get a passive circuit to give you what you need.

Regards,
Ray L.
Could you show the circuit to be realized ?

Thanks !

thatcadguy

dimare, check out that other topic I linked to, Wawa actually found a great solution -- Analog Devices has several chips that have an SPI interface and 0-20mA out so that you don't have to worry about voltages from the DAC. I am going to use an AD5420 myself.

dimare_gabriele

hello everyone ... after doing tests with the integrated ad694 , with poor results .. ( inprecisioni ) .. I found out that I can use as a 0-5V or 0-10V range also ... any of you know a Dashboard with i2c that communicates with arduino and output dAC converts 0-10v?

MarkT

Don't bother with the internal DAC on the Due, its very poor.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

GianniCarr

#11
Aug 12, 2015, 07:41 am Last Edit: Aug 12, 2015, 05:35 pm by GianniCarr
I have completely solved this problem using a simple operational amplifier. Look at my  site: http://ardupiclab.blogspot.it/  for the scheme and explanations.

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