Thanks for the tip. That sample rate is plenty
as long as other things can be done while the sampling continues.
I'll search Beaglebone PRU + ADC.
At 11:59 AM 10/30/2015, William Hermans wrote:
BBB and Linux are new to me. One of the things
I would like to do is compute a ratio between
two voltages, each of which might exceed 1.8
VDC. One solution might be to use DACs to sent
feedback voltages to operational amplifiers that
are supplied by 1.8 VDC. The goal is to
determine the ratio as quickly as possible and
without waiting for Linux to get around to it (waiting for the ADC to happen).
[]
What sample rate do you need ? If something
around only a few thousand samples a second.
This can be done from userspace without using
the PRU's. You can even use mmap() with
/dev/mem/ and directly manipulate the ADC's
registers, which can sample the ADC faster than
200ksps. However, the sample rate would not be
as deterministic as using the PRU's.
You can use a PRU to read the ADC's for sure. If
you search the web for Beaglebone PRU + ADC
, you will find many ways. People have been
doing this for a long time( since the beaglebone
white ), and if you search this google group,
you'll even find full code for something someone
called "ADCcollector". It's C, and PASM
assembly, but is a very short / easy read / understanding.
As for how to physically connect to the ADC, I'd
listen to evilwulfile. He's been an EE for
longer than many people on this group have been
alive, and he knows his stuff ( I know him
personally ). Don't risk burning up your board,
as I've seen several people on these groups do . . .
On Fri, Oct 30, 2015 at 9:43 AM, TJF
<<mailto:[email protected]>[email protected]> wrote:
Hi John!
As Przemek mentioned, a simple voltage divider
can scale the input voltage. Additionaly I use a
LED (orange color) between the ADC input and
ground in order to block overvoltage. (The LED
starts to light up at 1V5 and consumes full
power at 1V8. 1 / 6 of the ADC resolution get
lost (is less accurate), but the burning LED as
indicatior is a nice side effect.)
Regarding software you should have a look at
<http://hackaday.com/2015/02/16/library-upgrade-to-pru-gives-fast-io-on-beaglebone/#comments>libpruio.
BR
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