On 28/10/12 15:46, Dan wrote:
If the "grounding problem" you're worried about is magnetic pickup, then one traditional solution is:
- start with a wire twice as long as you need
- bend it round a fixed support at its half-way point
- sticky-tape both ends of the wire to the chuck of a power drill
- turn the power drill on for a few seconds
- cut the wire at the bend.
Hey presto, you've got signal and ground wires in a twisted pair.
That only really helps for balanced line or differential signalling and tbh electrical noise on a battery voltage you are monitoring isn't going to make much of a difference anyway.
It's a common misconception but twisting pairs doesn't magically reduce interference. What it does when you have differential signalling is ensure that both sides of the pair are subjected to the same electromagnetic interference at the same amplitude. Thus making it easy for a comparator to subtract the noise out.
The grounding problem Chris may have is twofold.
If the things he is monitoring don't share a common ground then he doesn't have a common point to tie the analogue ground of the A/D converter.
If he measures upstream from the batteries on their feed wires then his local ground will have a DC offset to the battery negative post, particularly under load. The reason is that the voltage drop in the battery cabling affects both sides of the circuit. So it would be fairly easy to create an unintentional ground loop.
Chris now tells us that the batteries are grounded to the hull things have become a bit simpler (as long as his ground straps are all good).