Dwayne: Interesting question - I built my own shunt circuits on a protoboard so I was able to bring out a connection to P9_34.
After looking at the BBB schematic, I see there is a ferrite bead connecting GNDA to GND, so there is continuity between them and you should be able to use the GND on positions 1 or 10 of X1. -Steve > On Feb 2, 2021, at 8:47 PM, Dwayne Zimmerman <[email protected]> wrote: > > Steve > Thanks that helps a lot, but the agnd is not actually brought out to the > terminal strip only the gnd. How do I attach to agnd? > > On Tuesday, February 2, 2021 at 8:27:25 PM UTC-5 [email protected] wrote: > The comms board 4-20mA current loop input consists of a 75Ω shunt resistor > across one of the analog input pins. > > You need to connect an appropriate voltage source to your device and the > other end of your device to the comms board input. Connect the ground of > your voltage source to the Analog Ground pin. > > Divide the measured voltage by 75 to obtain the current. > > The cape does not provide a voltage source, Many devices use 24V excitation, > but this is not universal. Thus the choice of voltage source is left to you. > > Hope this helps someone. Schematic can be found here if you have any doubts: > > https://github.com/beagleboard/capes/blob/master/beaglebone/Comms/Comms_Cape_sch.pdf > > <https://github.com/beagleboard/capes/blob/master/beaglebone/Comms/Comms_Cape_sch.pdf> > > > > > > >> On Feb 2, 2021, at 8:14 PM, evilwulfie <[email protected] >> <applewebdata://6533244C-6674-46AB-AABD-B923B79C5C1D>> wrote: >> > >> you can use an current to voltage converter then an opamp to level shift it >> >> On 2/2/2021 5:03 PM, Dwayne Zimmerman wrote: >>> Can anyone tell me how to connect a sensor to the 4-20mA input on the comms >>> board.I need temperature and all 4-20mA temperature sensors I'm familiar >>> with are 24 VDC not 1.8 >>> >>> On Monday, February 1, 2021 at 7:29:46 PM UTC-5 Dennis Bieber wrote: >>> On Mon, 1 Feb 2021 15:46:51 -0800 (PST), in >>> gmane.comp.hardware.beagleboard.user Dwayne Zimmerman >>> <[email protected] <>> wrote: >>> >>> >So the pull down is to keep the voltage under 1.8 correct? My confusion is >>> >I have one screw per input, 4-20mA is two wire where is the other half of >>> >the circut? >>> > >>> >>> I suspect the pull-down is only ensuring that the floating voltage is >>> tied to 0V; feeding anything with a voltage over 1.8V will still fry the >>> input. And since 0V likely also means 0mA, it indicates a fault condition >>> in the loop. >>> >>> https://www.fluke.com/en-us/learn/best-practices/test-tools-basics/process-tools/what-is-a-4-20-ma-current-loop >>> >>> <https://www.fluke.com/en-us/learn/best-practices/test-tools-basics/process-tools/what-is-a-4-20-ma-current-loop> >>> >>> https://www.predig.com/indicatorpage/back-basics-fundamentals-4-20-ma-current-loops >>> >>> <https://www.predig.com/indicatorpage/back-basics-fundamentals-4-20-ma-current-loops> >>> >>> {Many others| >>> >>> The input to the BBB likely needs to consist of a current->voltage >>> tranform, so the ADC can measure the voltage corresponding to the current. >>> Which might be built-into the cape (I've not looked at it). >>> >>> >>> -- >>> Dennis L Bieber >>> >>> -- >>> 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] >>> <applewebdata://6533244C-6674-46AB-AABD-B923B79C5C1D>. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/beagleboard/5fd03d5f-b21f-43b8-b3d3-ae464ff8d1bdn%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/beagleboard/5fd03d5f-b21f-43b8-b3d3-ae464ff8d1bdn%40googlegroups.com?utm_medium=email&utm_source=footer>. >> >> >> -- >> 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] >> <applewebdata://6533244C-6674-46AB-AABD-B923B79C5C1D>. > >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/9654dc5a-2d31-6f0f-a745-ae085db30859%40gmail.com >> >> <https://groups.google.com/d/msgid/beagleboard/9654dc5a-2d31-6f0f-a745-ae085db30859%40gmail.com?utm_medium=email&utm_source=footer>. > > > -- > 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] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/9f22b7ef-9eff-4f16-aa73-65fe71c9ff0dn%40googlegroups.com > > <https://groups.google.com/d/msgid/beagleboard/9f22b7ef-9eff-4f16-aa73-65fe71c9ff0dn%40googlegroups.com?utm_medium=email&utm_source=footer>. -- 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/2DA78AAC-6FAE-43C2-8DDB-4A31947EB198%40gmail.com.
