A few system grounding questions

[gonzobrian]

I'm building a 3 CP cocktail cabinet.

[ShinAce]

I read the first have of your post, but not the rest as I'm already confused.

Here's what I CAN tell you. Sometimes, you MUST share grounds. For example, I've been doing this(EE) a while and the other day I slipped up. I built a stick that has a 12 volt battery in it. Power is regulated to 5 volts and sent out from the stick to other modules. These include a module with LED's. The lights activate with button presses, so I use it for troubleshooting. The stick even powers the pad, for no good reason. Actually there is, I can leave it plugged into a console and turn off the stick itself and it's no longer recognized.
At any rate, I was hacking a USB pad to a db15 connector. I hacked the ground and power wires to the db15 connector, but forget to keep a ground intact for the USB cord going to the computer. Without that ground connection, the computer has no reference for the signals coming in, and they are therefore meaningless. Sure enough, it's like the pad isn't even plugged in at all. So after 15 minutes of dicking around, I slapped my forehead and fixed it.

Signals 101: Always share the ground.

History 101: Ground does in fact stand for EARTH. This planet is a huge battery, and driving a stick in the ground allows you to have a true earth ground, very important in stuff like amateur radio. It's an "absolute reference" point, nothing more.
Normally we just tie the negative end(0 volts) of all circuits together and call it a ground, which is a pretty good depiction of an earth ground.

Ground loops happen when large currents are allowed to travel through uneven(in terms of length) ground paths. A current on one can induce a current on another ground wire, hence the loop. This is normally avoided by simply connecting all grounds to a common point. So that's why you see people soldering grounds to a washer bolted somewhere, because it makes it easy to add more grounds.

One last thing, there are MANY types of lights, from incadescent to fluorescent to solid state. Fluorescent lights have MASSIVE interference problems, but it's very unlikely to be in the audible range.

[gonzobrian]

Wow thanks for the 101
When I said ground loop.

[pcb]

Is there any problem sharing ground with the lights for the coin door?

[gonzobrian]

So is there any reason I can't just ground the lights directly to the computers wiring harnes.

[pcb]

So is there any reason I can't just ground the lights directly to the computers wiring harnes.