Or 4024 * 1.8 / 4096?
On 10/30/2015 12:18 PM, William Hermans wrote:
By the way, the ADC gives out a value of 0-4095. So scaling voltage is
really simple. Say you get a value of 4024 for a reading. In order to
get a reading from 0-1.8v from this . . .
((4024 / 4096) * 1.8) or 1.768359375v
The max voltage on the pins still can not exceed 1.8v, this is why one
needs an opamp, or similar device to keep the input scaled down. But,
in this manner you could even track large voltages. Hundreds or even
thousands of volts, at the cost of resolution. Which unfortunately can
not be avoided. So going by the above example . . .
((4024 / 4096) * 300) or 294.7265625v
Does this make sense ?
On Fri, Oct 30, 2015 at 9:59 AM, William Hermans <[email protected]
<mailto:[email protected]>> 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 <[email protected]
<mailto:[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 libpruio
<http://hackaday.com/2015/02/16/library-upgrade-to-pru-gives-fast-io-on-beaglebone/#comments>.
BR
--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the
Google Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from
it, send an email to [email protected]
<mailto:[email protected]>.
For more options, visit https://groups.google.com/d/optout.
--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the Google
Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected]
<mailto:[email protected]>.
For more options, visit https://groups.google.com/d/optout.
--
Chad Baker Memphis, TN
--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the Google Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
