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 :-)
<https://lh3.googleusercontent.com/-G4DoP46BTVo/WkKXV2NZU2I/AAAAAAAAAB8/rDvGmWBeon0EWK4RPaiO4vUGOthBvyQpQCLcBGAs/s1600/AIN.png> On Wednesday, December 20, 2017 at 4:29:44 PM UTC+1, Adam Saenz wrote: > > Forgot to add that you should use the GNDA as the ground reference to your > external analog input sources. > > Adam > > On Wednesday, December 20, 2017 at 6:57:26 AM UTC-8, Adam Saenz wrote: >> >> You will need to use a voltage divider to lower the detectable voltage of >> your 0-5V or 0-10V inputs to a range of 0-1.8V or less. Google voltage >> divider to see how this is done; sparkfun provides a pretty nice >> explanation of voltage dividers. If you look at the schematic, an example >> of a voltage divider is done for AIN7 to read the 3.3V supply voltage. >> AIN7 will see is 1.65V when VDD_3V3B is 3.3V. >> >> ADCs are most accurate when the voltage they are reading is stable and >> free from noise or ripple voltages. Digital circuits (e.g. the processor >> cor) are sources of digital noise so a separate VADC and GNDA are provided >> to minimize the influence of noisy digital sources. If you look on the >> schematic VDD_ADC is actually connected to VDD_1V8 through a ferrite bead >> (inductor). The ferrite bead is there to block high frequency noise caused >> by the digital circuits, while allowing DC voltages to pass; so VDD_ADC is >> actually connected to 1.8V. The AM3358 datasheet lists the max voltage >> input of VDD_ADC as 2.1V so you cannot connect a 5V or 10V reference >> directly to it. It's best to use the existing 1.8V reference and scale the >> analog input voltages you want to measure so they are less than 1.8V. >> >> Adam >> >> >> On Wednesday, December 20, 2017 at 4:46:11 AM UTC-8, mike.ma...@gmail.com >> wrote: >>> >>> Hi, >>> >>> this is somewhat a noob-question, but my skills in analogue hardware are >>> limited. >>> >>> The BeagleBones (and variants) come with six analogue inputs which each >>> have a separate ground line GNDA and also a separate power supply VADC. >>> >>> My questions here: how can I connect an external signal with 0..5V or >>> 0..10V to these inputs in order to read their analogue value? >>> >>> And how about GNDA, has it to be separated from normal GND? >>> >>> Thanks! >>> >>> Mike >>> >>> -- 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/7791a34d-72df-4dd8-92eb-ff4644ce2a74%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
