Using case as ground?

Hi all!
I'm building a midi controller for my band. It will be contained within an aluminium/steel chassis (about 30cm x 45cm x 20cm box) and running with Arduino Mega. I'll be using pretty much all the analog and digital ports and I'm trying to consider ways of reducing the amount of wiring inside the case. So I thought why not connect Arduino's gnd to the case with a small wire and then just connect all the other component's grounds straight to the case. This would reduce a lot of the wiring.
I already tried this with a single led and it seems to work. But before I go on taking the gigantic task of putting all of this together I want to make sure I'm not doing anything insanely stupid. Are there any defects to this approach? Could multiple components mess it up? Any tips very apprecciated.
I'm quite new to electronics :-[ Also tried googling the web and forum and couldn't find anything on this.


My trucks and motorcycles are wired this way. I see no reason for the electrons involved to be picky about traveling through the case, instead of a wire.

Unless it's a plastic case. Or the band is awful and the electrons don't want to listen to the music.

Or maybe the music is so good the electrons all want to stop and listen, instead of getting to work.

In all seriousness, whether the ground is a wire or a metal plate will make no difference.

I'm glad we're so mediocre. The electrons won't bother to pay attention. Thanks for the prompt response. I'll get to work!

for my band.

Common practices (words to live by):

Bands usually have lots of stuff hooked up (with wires) on stage. Microphones, instruments, amplifiers, etc. For safety sake, any exposed metal should be connected to earth ground unless that part of the system is totally isolated from power mains (through a low-voltage transformer, for example). You should never intentionally cause any kind or any magnitude of current to flow through earth ground in any part of your system. Period.

For signal integrity (best noise immunity), there should be no signal path from one point in the interconnected subsystems to another point that involves earth ground.

If you have several different circuit assemblies inside a box, connect their signal grounds together, preferably at a single point. Do not connect signal ground to the metal enclosure.

Signals that go (through wires) from one subsystem to another subsystem should, ideally, be connected through shielded cables. The shield on the cable may or may not be common with earth ground and it may or may not be connected to the metal enclosure, but it is not used for signal ground.



Thanks for your tips. However, I'm finding myself a bit lost. Are you saying I shouldn't use the case as ground?
The arduino is powered by usb from a computer hooked up to earth ground.

There's also a power source from an old computer inside the controller which is used to power certain lights with 12V. The power source and the lights are separate from the Arduino circuitry - not connected in any way except that the power source is in touch with the metal enclosure. Not sure if this is important...

Assuming that you're not doing anything with an audio signal (google 'ground loop' for info), or maybe high speed digital comms, then it should be okay to use the case for low current 0V/Ground connections.

As stated in another reply, it's standard practice for vehicles.

However, as also stated before, connecting 'earths' to a single point (star earthing) is good practice and things like this (and segragating earths for power, audio, comms etc.) can help to reduce noise etc.

Does serial data via usb count as high speed digital comm? Does using the case as ground signifigantly add noise to analog components such as potentiometres?

You might get lucky and have no problems. But it is NOT good engineering practice.

I'm going to point out here that connecting anything to the case can turn out to be a very bad idea, take apple's decision for example ;D

While the electrons certainly don't mind travailing through a case, the problem is that they are often joined by other unwanted electrons. If a case must be connected to a supply then it should only be done at one point, this is to avoid you getting ground loops. This is where you get currents flowing between the grounding points because they are of slightly different potentials, even though they are nominally ground. Also a mechanical connection to a case is electrically prone to tarnish and increasing the resistance over time.

Finally as a note that professionally when ever I connect a case to a supply this is done through a low ohm resistor. This is to stop cavity resonances generating excessive electromagnetic radiation. This is important for approvals in most countries.

Thanks for all your help. I guess I’ll be a good engineer and not use the case as ground after all.

Though I must clarify that the power source (standard ATX) was never meant to be grounded to the case - I mentioned it because it touches the case. I thought this might have some effect on something. Otherwise it’s complete isolated from the rest. Its only purpose is to power the cold cathode lamps and look cool. It’s powered like any desktop computer is.

Also, the controller does not handle audio in any way. It’s pure serial data (converted to midi via software) to the computer.