> > *Or 4024 * 1.8 / 4096?* > Ok, so let us put this another way. Do you think that is clear when written in code ? What if 1.8 were actually assigned to a constant pointer ?
On Sat, Oct 31, 2015 at 5:01 AM, Chad Baker <[email protected]> wrote: > 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]> > 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]> >> [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> >>> 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]> >>> [email protected]. >>> For more options, visit <https://groups.google.com/d/optout> >>> 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]. > 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. > -- 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.
