Great, thanks to all :-) On Wed, Dec 27, 2017 at 2:35 AM, Adam Saenz <ajsa...@gmail.com> wrote:
> That circuit will work. Yes on connecting external ground to GNDA, that > will give you a common reference. Those resistor values will allow the ADC > to see about 1.78V when the input voltage is 5V, looks like a good place to > start. As far as resistor values (1k, 1.8k vs 10k, 18k), I'd go with the > 1k, 1.8k pair as long as your source circuit can handle sourcing a 2.8k > load (1.7mA max). If it can't then I'd consider something that gives you a > total resistance of 5-6k. The 10k/18k pair gives you 28k total, should be > ok but I've had ADCs have trouble working when resistances approach 100k. > > Someone mentioned using op amps which is a good choice, as is using an > anti-aliasing filter but since this is a noob type question I figured > starting simpler is a better choice. You can improve you analog circuit if > you discover your application needs to minimize noise, or is sensitive to > load, etc. Start simple though. > > Adam > > On Tue, Dec 26, 2017 at 10:58 AM, Dennis Lee Bieber <wlfr...@ix.netcom.com > > wrote: > >> On Tue, 26 Dec 2017 10:40:54 -0800 (PST), >> mike.maikae...@gmail.com declaimed the >> following: >> >> > >> > >> >So it could look like this!? External ground is directly connected to >> GNDA >> >and the relation between the resistors is equal to the relation of the >> >voltages to apply at each!? How about the exact resistor values - 18 kOhm >> >and 10 kOhm would be the same from relation, but which one should I use >> >really? Thanks :-) >> > >> >> How much current flow can you accept? Consider, without the >> resistors >> you basically have a direct short from the input voltage source to ground. >> Small value resistors will let a lot more current pass. You likely need to >> balance between not having too much current flowing through the divider >> and >> having so little current flowing that the ADC can't sense the voltage... >> >> -- >> Wulfraed Dennis Lee Bieber AF6VN >> wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.com/ >> >> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to a topic in the >> Google Groups "BeagleBoard" group. >> To unsubscribe from this topic, visit https://groups.google.com/d/to >> pic/beagleboard/jK1moLhBsHc/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> beagleboard+unsubscr...@googlegroups.com. >> To view this discussion on the web visit https://groups.google.com/d/ms >> gid/beagleboard/el654d1r4scdqhe8dd4fnge0404dp79n32%404ax.com. >> 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 a topic in the > Google Groups "BeagleBoard" group. > To unsubscribe from this topic, visit https://groups.google.com/d/ > topic/beagleboard/jK1moLhBsHc/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > beagleboard+unsubscr...@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/beagleboard/CAJL9%2B4%2B9mSCOGwwu1KUmpE_LGLd9f%2B52- > DkUWc41kbUptpUiCw%40mail.gmail.com > <https://groups.google.com/d/msgid/beagleboard/CAJL9%2B4%2B9mSCOGwwu1KUmpE_LGLd9f%2B52-DkUWc41kbUptpUiCw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > 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 beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAG%3DKTckz8uXdpC%2BE%3DXPODSvxJDVxeHQdaoS5x5EhTesqQh1nWA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
