Hello,
at https://books.google.de/books?id=Udu6BQAAQBAJ&pg=PA344&lpg=PA344&dq=beaglebone+adc+op+amp&source=bl&ots=CZagSBqMui&sig=cLXCgstuc51TzoBRzMzB81RcJyU&hl=de&sa=X&ved=0ahUKEwjZ6-LovKTSAhXJXBQKHfktBio4ChDoAQhJMAk#v=onepage&q=beaglebone%20adc%20op%20amp&f=false a wiring scheme for the analog inputs is described which protects the BBB/BBG from overvoltage.
Amazingly they connect AGND and GND with each other. Is this really a good idea?
Thanks!
Hello,
at https://books.google.de/books?id=Udu6BQAAQBAJ&pg=PA344&lpg=PA344&dq=beaglebone+adc+op+amp&source=bl&ots=CZagSBqMui&sig=cLXCgstuc51TzoBRzMzB81RcJyU&hl=de&sa=X&ved=0ahUKEwjZ6-LovKTSAhXJXBQKHfktBio4ChDoAQhJMAk#v=onepage&q=beaglebone%20adc%20op%20amp&f=false a wiring scheme for the analog inputs is described which protects the BBB/BBG from overvoltage.
Amazingly they connect AGND and GND with each other. Is this really a good idea?
Well, at some point they are always connected. What you want is for them to connect only at one point and that point should be closest to the power source. Think of a star connection, with the center of the star as the reference ground point. What you don’t what is digital signals flowing through the analog ground and that occurs when you connect AGND to DGND at more than one point.
Regards,
John
So when I understand this correctly: in layout of a board they should be
connected with each other as close as possible to the BBB/BBG expansion
header connector?
As close as possible to the power source GND. So if you intend to use the barrel connector to power the board, the GND and AGND should connect at the barrel connector GND pin, or if you use the expansion connector to power the board, then connect GND and AGND at a single GND pin on the expansion connector. I does not matter that several GND pins are connected to the GND plane. I hope this helps.
Regards,
John