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[on:]

I'm designing a low-speed network system with very small nodes, typically 1x1", that will (often) be encapsulated in potting boxes.

My problem is that I can't decide on a suitable connector to specify.

Relevant features are

• The physical layer of the network is RS-485 plus GND and power, thus four wires.

• Each node must have two connectors for easy daisy chaining.

• The connector must be readily available, no weird-arsed mil-spec job that nobody can buy.

An obvious choice is RJ45 being an industry standard and all, but they are so large they actually don't fit the preferred 1x1" form factor (although I am prepared to change this). Also these would be difficult to bring out of a potted enclosure although vertical jacks would work OK.

Another option is a 4-way 3.5mm audio plug but I'm not convinced they are all that common and would be worried about reliability and messy soldering of wires.

And then there's 4-way headers, not really a good look and once again maybe not that reliable as they are easily pulled out.

Any ideas out there?

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Rob

[Reply #1 on:]

And using blue Screw Terminals like these? - http://www.sparkfun.com/products/8235 - Over 4000 in stock, can be connected with any kind of wire, without the need for special connectors on the wire, just strip & screw.

Rob

[Reply #2 on:]

Possibly, my initial idea was to have screw terminals because no fancy tools are required, I was going to use something like a Phoenix .2" plug in terminal, but they are pretty large.

However those ones are only 3.5mm pitch so I'll look at the specs.

One thing I have against screw terminals is that you can't just unplug/replug, but on the good side they are a no-brainer to connect to.

I guess USB is another option with really small connectors, but AFAIK you can't make your own cables up.

This is supposed to be easy for the average hobbyist to use, so requiring a $50 crimper goes against that.

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Rob

[Reply #3 on:]

Screw terminals are indeed a no-brainer, low cost, reliable and therefor ideal for low budget hobbyists. They are also very easy to check if they work, and you can hold a voltmeter or a scope against the screws what can be easy during "debugging" too.

A few weeks ago there was a similar discussion about what kind of connector to use for some sensor. Earphone plugs and alike were discouraged as they go short circuit when un/replug. and maybe a short doesn't damage the hardware, it certainly disrupts communication when unplugged alive. People will do that, especially if you warn them they shouldn't

[Reply #4 on:]

RJ11 phone connector has four wires and is a bit smaller then rj45.
The plugs, wire and crimping tool are available in most hardware stores (at least where I live) and are pretty cheap.

Liudr is using this one on his Phi-1 shield.

http://www.dipmicro.com/store/JACK-FRJA-614

[Reply #5 on:]

Hmm I'd forgotten about RJ11, I like the small flexible cables and positive click (just like RJ45) and IIRC there are 100s of cheap premade cable lenghts in any phone shop.

The socket however is hardly any smaller than RJ45, even a 4/4 is 18x14mm.

Another thing is the 24 gauge wire (some even 26), I need to run power and I wouldn't get much down that with a long run.

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Rob

[Reply #6 on:]

wortlesoft

I just realised that when daisy chaining you can't use normal "straight through" cables because the signals get swapped. This means crimping "crossed" cables with one connector on the opposite way to the other.

The 6-way phone cable is physically symetrical right? I can just crimp the connectors either way?

This is not a problem with screw terminal blocks of course, but I can't see how to mount them clear of the potting mix without machining the box.


______
Rob