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/8c75e48e-a7b2-449c-ab8b-d02307d53370%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
