Hi there. I have an application where an Arduino Mega will be controlling some equipment in a remote location. The package will be deployed for 2 years. The Arduino will be mounted vertically on a plate, but once deployed it will not move and there should be minimal vibration.
Can anyone recommend some fairly reliable connectors we could use? I'm interested mainly in the double-row of digital pins (pins 22-53). Ideally I'd like a complete cable assembly so I don't have to do any soldering or crimping. At the moment the best I can come up with is a dual-row header coupled to a female IDC socket.
Discrete wires would be ideal, if anyone has come across anything like that. Thanks so much for the help.
Mounted vertically or horizontally really matters not. Remote location to me means remote as in not readily accessible. What you fail to mention is environmental conditions? Things like temperature and humidity are key players. Personally I like hard wired including solder joints but if a friendly environment that maybe just a proto-type screw terminal terminal block shield. All depends on the environment.
Look a the connectors on the Mega to see if they are tin or gold. I suspect they are tin.
Places like Digikey & mouser have cable assemblies or IDC connectors which can be mated with a ribbon cable by squeezing in a vice. The connector pins MUST match the mega connector. Mating Gold to Tin is not better than tin - tin. You will probably have to cut off at least part of the shroud that comes on this type of connector.
You could use strip pins to plug into the connectors then solder wires to each pin. Would be a pain though. If you do I would strongly suggest you use silicone insulated wire with high strand count. This can be found on ebay. This wire is extremely flexible and soldering friendly and will greatly reduce the risk of breaking wires at the solder joint.
Thanks so much for the quick responses. The arduino will be in a sealed enclosure, sitting in about 30 m of seawater. Water is around 10 degC year-round, so we estimate the internal temperature of the enclosure to stay under 30 degC. Humidity should be minimal (or else we're screwed anyway). The enclosure is mounted on a frame with a lot of other equipment, and we have cables running to a shore station to provide power and communication. Once deployed, we have no access to it until the scheduled recovery date - around 2 years after deployment.
I don't want to try soldering to a male header - too many wires, too many points of potential failure given my soldering skills. I was looking at the IDC connectors, but I could only find female versions (that were in stock anyway - 3M makes a male version, but no one seems to carry it). That's better than nothing, of course. I can plug the female IDC into a male header strip, and then plug that into the Arduino. And maybe a bit of glue (like E6000 or similar) to make sure they don't come apart.
I'm just surprised that, given how many Arduino accessories you can buy, no one makes a pre-assembled connector.
I would always look to locate the Arduino somewhere better and run leads to whatever you are measuring. I would be looking at a dedicated board for a job like this , potting maybe ?
10M of water , means the enclosure with be subject to about 1 ( extra) atmosphere of pressure - you’ll need a specialist enclosure for that if it’s not to leak long term . There will presumably undersea current which will move it around too.
I am seeing breakout boards like this one with screw terminals. Then there are some, like this one, which include an IDC connector in addition to screw terminals. Unfortunately the latter is for an UNO board. If you go with an IDC and ribbon cable there are IDC to screw terminal adapters to get you back to screw terminals. If routing becomes an issue using ribbon cable they do make rolled round ribbon cable.
Thanks again for everyone's help with this. I should have given more information about the project. This isn't a DIY hobby project, it is providing a system to monitor for marine mammal interactions with tidal turbines off the northern coast of Scotland. I work at the University of St. Andrews, and we are building up a system that uses both passive acoustic (hydrophones) and active (sonar) monitoring to watch/listen for dolphins and porpoises.
The Arduino will be controlling a number of pieces of equipment - linear actuators to help with sonar orientation, pan/tilt/roll sensors, UV lights to limit bio-fouling, and power management to various devices. The enclosure integrity won't be a problem, it's rated for much greater depths. The wet-mate connectors cost more than my car. There are very high sea currents (has to be - that's why the turbine is there) but the entire assembly will weigh close to 2000 kg so it should be stable.
We get most of our electronics from Mouser, but I haven't been able to find cables with male connectors in stock. 3M makes some, but they are all special order and high min quantity. That's how I ended up with the IDC females and the male headers solution. The breakout board is amazing - thanks for that link, I've never seen those before - but unfortunately we have an ethernet shield on top so we can't use it. Too bad, it would be ideal.
I have found some by Samtec (HCMD and IDMD series) that have a 2 month lead time but I think I can order just one or two. I'm going to explore that, as well as look into breakout boards. Again, thank you everyone I really appreciate your help.
The arduino will be in a sealed enclosure, sitting in about 30 m of seawater. Water is around 10 degC year-round, so we estimate the internal temperature of the enclosure to stay under 30 degC. Humidity should be minimal (or else we're screwed anyway).
In my experience, seals don't. I say this from experience, though not in sea water.
For two years you will need a hermetic seal (metal to metal, like solder) and you need to back fill with very dry air and / or add a number of desiccant packs.
Also sealing wires entering a sealed container is an art. I guess I'm assuming there is some I/O from the box.
To satisfy your skepticism, take you container / box etc and with nothing in it drop it in the water for a week. See how it works.
Regardless of how you create your enclosure you should coat the Mega and any other boards with a Spray silicone conformal coating. You should find plenty of options on the internet.
Thanks for the suggestions. We're doing a trial deployment at some point - originally it was to be in June, but that's obviously pushed back now. Desiccant packs are a great idea, we'll definitely add those into the enclosure. And a conformal coating as well.
You can put headers on a stripboard that plugs into an Arduino, but the odd pin spacings for the D8--AREF
are a pain (hint two pieces of stripboard glued to a common substrate works). This spacing issue
is a historical error, a failure to double check a PCB layout in the cold light of day I suspect!
You can even make a PCB copy of the Arduino (open source), and either populate it or give it headers
and plug in an Arduino, which is quite clever way to leave options open. Then all your interface stuff goes
on the PCB as a custom shield, but outside the Arduino footprint.
You didn't mention what type of seal you were anticipating using, nor if there are wires entering and exiting the enclosure.
After additional time to think, if you have to do this, I would seal the enclosure with RTV. You might be able to get away with GE silicone II, the stuff that doesn't smell like acetic acid. It's less corrosive. Also thinking you should have as large a sealing surface as practical.
I don't know if this is worth doing, but you might consider sealing it with a positive pressure inside.... say 30+ meters of salt water
Sorry for the silence, had to work on other projects for awhile. Thanks again for everyone's help - based on the responses, I stumbled across the Mega breakout boards from Robert Patterson (Cross Roads Electronics) and ordered one. And if somehow it doesn't work out for my application, I have cable ideas to fall back on.
The enclosure is sealed with a double-row o-ring barrel seal. The connectors are from Hydrobond, the HDM series with both a compression seal and barrel seal. I understand the hermetic seal suggestion - I worked for many years with a company making mass spectrometers and have had to deal with vacuum components in mid- and high-vac environments. But that doesn't really seem to be an option - o-ring seals seem to be the standard for subsea equipment, and we don't have the budget to go for a completely custom design. RTV would probably still be a good idea - a little extra insurance can't hurt.
We had a system out for 2 years already, and there was a small leak through one of the connectors but we think that was due to corrosion issues and less-than-ideal o-ring placement.
We don't have the equipment to pressurize it before deployment, but I'll look around. It's a big university, and some other departments may have something useful. My worry is that it will require an extra valve, and every component I add becomes a potential leak source. We'll see.