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, [email protected] 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/4f3a7e4d-eceb-47bb-9be7-7e04ee1997b9%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
