ANALOG/ DIGITAL .NOISE

[Fritz Oppliger]

In a ribbon cable I have analog signals on one side, digital stuff on the
other edge. I found the digital traffic was influencing the analog so I
went to a wider ribbon cable. better separation. Now I have a couple of
unused conductors in the middle.

Do I connect these unused wires to:
analog ground
digital ground
earth ground
leave unconnected

If this looks like homework, well it IS, in my homebrew electronics
self-education.
I could have the connections jumper- selectable.
from the sublime to the ridiculous.
I value your opinions first.
Thank you.

 

[Michael A. Covington]

I would vote for analog ground.

 

[Kevin Kilzer]

In a ribbon cable I have analog signals on one side, digital stuff on the
other edge. I found the digital traffic was influencing the analog so I
went to a wider ribbon cable. better separation. Now I have a couple of
unused conductors in the middle.

Do I connect these unused wires to:
analog ground
digital ground
earth ground
leave unconnected

Do not connect them to earth ground. It is too much hassle in most
systems. E.g., where is "earth" on a 9V battery? Also, it probably
leads to other, weird problems.

I would vote for digital ground, because this will prevent the digital
currents from being forced into the analog ground paths. There are
other ways to guard against this, but if you start with lower digital
ground noise you will probably be better off in the long run.

Kevin

 

[Rich Grise]

In a ribbon cable I have analog signals on one side, digital stuff on the
other edge. I found the digital traffic was influencing the analog so I
went to a wider ribbon cable. better separation. Now I have a couple of
unused conductors in the middle.

Do I connect these unused wires to:
analog ground
digital ground
earth ground
leave unconnected

If this looks like homework, well it IS, in my homebrew electronics
self-education.
I could have the connections jumper- selectable.
from the sublime to the ridiculous.
I value your opinions first.
Thank you.

If you have more than one wire in the middle, use half for digital
ground and half for analog. If there's an odd number, digital gets
the odd one.

Cheers!
Rich