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Topic: Making an electronics project survive (Read 548 times) previous topic - next topic

ill_switch

Hello all,

I've got a newbie-ish electronics topic for discussion that doesn't pertain specifically to Arduino so hopefully I can get some feedback in here.

I've got enough of a background to solder things together and write code, but I'm really a self-taught hack with some large holes in my knowledge. I'm getting ready to build my first substantial, permanent project and I'm hoping you can all help.

The topic I'm interested in is making a project "rugged" enough to survive in the real world. I realize this is a broad and hard to describe problem, but I'm at least looking for some pointers or good references to read on the subject.

Here's the situation. I'm going to have a big fish tank in my home, with an Arduino to control certain aspects of it (turning lights on and off, logging data, etc.) I've got prototypes working just fine, but they're on breadboards. Not exactly the sort of thing I want to stick in an environment that can be hot and humid.

So, how do I tackle this? My thoughts:

1) Put the Arduino in a project box. But what's the "best practice" for making connections to the Arduino itself? Are these little .1" breakaway headers really good enough, or do I need to use some other connector? Or solder directly to the board?

2) Once I've got connections made to the board, how do I penetrate the project box? Do I use a panel-mounted terminal strip and connect cables to the exterior? That would make removal for servicing convenient. Or, so I just run cables through grommets and connect internally?

3) What sort of connections can I use "out in the field" to connect sensors, etc.? I'll have some one wire sensors, and PWM signals from the Arduino controlling some devices.

4) In general, how do I determine what the max. cable lengths can be? For instance, if I have a PWM pin on the Arduino giving a signal to an LED driver, can the cable run be 1' long? 10'? Do I determine by experiment?

5) The environment is going to be electrically noisy, too. I'm going to have a VFD controlling a 1/2 hp 3-phase motor, which I've been told is "electrically very noisy." Do I need to provide some sort of shielding for the Arduino itself? What about One Wire and PWM cable runs? Do they need shielding?

Again, I realize my questions are probably wide open and I'm probably not providing enough info for anyone to actually answer, but can I at least get some pointers?

Thanks!

flyboy

It sounds to me like you will be using your Arduino in your home.  That means that you aren't likely dealing with temperature extremes.  That's one less thing to worry about.

How close are you planning to have your arduino to the tank?  Humidity could be an issue if you're really close, well, close to exposed water.  If you're a few feet away, you shouldn't have any problems there either.

1. A project box is probably the best way to enclose and protect your electronics.  There are a number of different electrical connectors that you can use.  Molex is readily available from Radio Shack.  You can also get some inline headers or other connectors from places like Digi-Key.  Probably not critical, unless you're using thermocouples.

2. This is going to be a matter of personal preference.  Space inside the box will help you decide this also.  You could use a terminal strip or a molex that "locks" into the hole.

3.  I've never used one wire sensors, so I don't know how sensitive the communications wires are to other communication wires if they're in the same bundle.  Might be good to consult the datasheets for the sensors on this one.

4.  If you're planning only to run lights, you can have wire several feet long with no problems.  When you get into situations where voltage is critical, you have to look at the number of Ohms per foot of a wire to help determine what gauge wire to use.  This is in the hundreds of feet range.  Not going to be a problem for you, I don't think.

5.  Since you're going to have a very noisy environment, you will probably want to use a metal enclosure for your arduino.  Be careful not to short anything inside it!  Your sensor wires may need shielding.  PWM for lighting shouldn't need any special consideration.

Hope this helps.  I saw several reads and no replies.  Happy building!

Grumpy_Mike

For reducing noise you need decoupling:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

For long runs of wires best add some protection to the raw processor pins:-
http://www.thebox.myzen.co.uk/Tutorial/Protection.html

Good luck  :)

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