really now. Prey tell, enlighten us then with your logic. On Mon, Nov 2, 2015 at 5:10 AM, Chad Baker <[email protected]> wrote:
> No, I don't, but having taught programming for over 40 years, I know that > students would take your equation and plug it in and then be surprised that > they get 0 for an answer. > > On 11/1/2015 6:13 PM, William Hermans wrote: > > *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]> >> [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]> >> [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. > > > > -- > 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. 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