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 <[email protected]> wrote: > On Tue, 26 Dec 2017 10:40:54 -0800 (PST), > [email protected] 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 > [email protected] 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/ > topic/beagleboard/jK1moLhBsHc/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/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 the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAJL9%2B4%2B9mSCOGwwu1KUmpE_LGLd9f%2B52-DkUWc41kbUptpUiCw%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
