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 stl...@gmail.com 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 > > > > > > On Feb 2, 2021, at 8:14 PM, evilwulfie <evilw...@gmail.com> 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 >> <dzimmermanpas-re5j...@public.gmane.org> 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.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 > --- > 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...@googlegroups.com. > 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 > --- > 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...@googlegroups.com. > > 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 --- 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/9f22b7ef-9eff-4f16-aa73-65fe71c9ff0dn%40googlegroups.com.
