thiagoralves
Hello friends,

Many people have asked me about the concept hardware that is on the OpenPLC website. The truth is that on the last two years I made a shift on the project to focus mostly on software instead of hardware, and therefore tried to support existing hardware boards instead of creating my own. This made the concept hardware become old, unsupported and kinda useless.

However, Petri Mantere (an OpenPLC user) wrote to me about an idea of modernizing the concept hardware and make it available for everyone. He is really good with 3D design and together we are trying to create a cheap, reliable, expandable and, of course, open source device that will work with OpenPLC software and will be better than any currently available board.

The idea is to have modules that are DIN rail compatible and can mechanically attach to each other providing expandability. A prototype sketch for the I/O expansion card is available here:  http://a360.co/2vpqvaK. If you want to 3D print the device, I've attached here the STL files for you.

The CPU card will be based on the NanoPi Neo (http://wiki.friendlyarm.com/wiki/index.php/NanoPi_NEO) which is an extremely cheap quad-core ARM Cortex A7 running at 1.2GHz. The CPU card itself will provide 6 digital inputs and 6 digital outputs, so that whoever wants to use only 12 I/O points only need to get the CPU card. Expansion cards will be added by stacking them on the CPU card. The bus will be an RS485 (just like the concept hardware), but the protocol to communicate with the expansion cards is probably going to be some sort of Modbus RTU implementation. Expansion cards will have dip switches to select their address in the bus, phoenix connectors in the front, and will be based around a cheap and small microcontroller (STM32F103, or ATMega328, or something else, I'm open to suggestions).

We want to make the whole device 3D printable, and we will also make available the complete parts-list and PCB project for you to build the whole thing if you want. Also, if I get enough funds, I plan to sell populated PCBs, printed cases and perhaps fully assembled devices for those of you that don't have access to PCB manufacturing or a 3D printer.

That is our idea, however, this is a community based project. So we would love to hear from all of you if you have any suggestion or idea to complete this project. I'm really, really, really excited about this!


Thanks,

Thiago Alves
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d6stringer
Awesome! I'll print up a case as soon as it let's me download it.

Let me know if you need any mechanical help.
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r2k-in-the-vortex
Why roll your own case? Commercially available DIN rail housings with built in electrical contacts come down to few dollars a piece and far surpass home-made 3D print quality that usually are craptacularly bad. 
Open Source ideology is worth something tho, so maybe select commercial housing, design the electronics to fit and then design an open source alternative case around the electronics.

That gives best of both worlds, user can just buy a good quality housing or they can play around with 3D printing if they prefer.

A random example:  http://uk.rs-online.com/web/p/din-rail-enclosures/6487699/
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thiagoralves
I've tried to look for commercially available DIN rail housings in the past, but all I could find was bulky cases that never worked for what I wanted. Even when I found something good, I end up having to drill holes on the case anyway to fit my custom connectors and peripherals (ethernet, power jack, etc). So in that case I just feel that it is simpler to have a 3D printed case that fits the device perfectly.
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d6stringer
I can't download the zip file. I'm getting this error: "Sorry! You don't have permission to perform this action. Please check your email for instructions on how to begin using your account. You can resend the email if you didn't receive it." 
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thiagoralves
This is weird, anyone should be able to download anything on the forum if they are registered users. It might be a glitch on the platform. Anyway, I'm sending you the file by email...
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r2k-in-the-vortex
Hmmzz... dunno, Phoenix has a pretty wide range of options, haven't even looked at other manufacturers.
The one I linked had 8 bus contacts and 12 IO ones, so I figured it might be a close fit, I think its just a matter of figuring out what exactly is needed and finding the right one.

It was in standard 17.5mm width format, I guess you could say its bulky compared to some commercial IO systems, but your case seems to be about the same, yours has less depth, but that is rarely an issue in most cabinets.
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d6stringer
First print of the box came out OK. I was using some old garbage PLA filament that i've been trying to burn so it's not the most pretty.  Some suggestions:

The walls should be thicker.  Many/Most home gamer extrusion based 3D printers will have a resolution of something like 0.3mm so if you are going to go small make the dimension divisible by a lot of sizes (eg 1.2mm 1.2/0.2 1.2/0.3 1.2/0.4) this will ensure part accuracy.  Try not to ever go below 4 layers if you can: most of the software for 3D printing will try to make 2 layers on each side of a feature (4 layers per feature).  Also, the materials that are 3D printable are pretty flimsy so err on the side of thick.

I would use circles instead of hexagons for the vents, though I do admit that I like the look of hexagons better.  The only reason is you get a better print quality with circles. If you want to stick with the hexagons, make the vertices point up.  This gives the printer something to build on.

Add a print support to the rectangular opening.  While most 3D software can do this for you, I always get better results when I design them myself.

Oversize all of your holes and maybe rethink your fasteners.  I find that almost all 3D extrusion printers make holes too small.  You can't calibrate for every printer but you can oversize the holes by ~1mm on this scale to get the holes size you want.  I prefer captive nuts and they are easy to incorporate in 3D prints.  Also press nuts work but these look to be a bit small for those.

20170907_133010.jpg 
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d6stringer
The second part, the lid has some of the same problems as the box but they were amplified by the geometry.
This part definitely needs to be thicker but it also needs to have a rim to positively engage with the box and add rigidity.  20170907_141719.jpg 
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Petri Mantere
It is really nice to get honest feedback (and I really mean it). Thank you for everyone.

It is a good point that commercial cases are more consistent and potentially cheaper too. However, I personally like flexibility and openess of the custom design. If somebody needs case that is for example 3 units wide, he/she can design and print it.

I made test print of my own and it come quite ok: https://drive.google.com/file/d/0B1r-PL1nuu5LZUhIMlZRRFJGNHc/view

It is good point that walls could be thicker, and generally design could be a bit easier for printers/slicers. I will make some changes to the next iteration.

Hexagonal vent holes looks nice in CAD but not in printed parts, I have to come up something else. Maybe angled slots or something.

I agree, front panel slots will need some support. It is probably best to add the support structure into model.

There could be more tolerance for fasteners, but I kind of like the idea that they are threaded into the plastic. It is not the most elegant, but very cheap and works in practice (as long as printer prints accurate sized holes).
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mvdiogo
hi, i am working with one project that could be open too. I am using atmega328, the easy chip to use.
This is the case
https://www.tinkercad.com/things/7NfL0rJoqo9-case
this is the clp made with fritzeng (the easy pcb edit ever)
https://drive.google.com/file/d/0B5slkWt0r6LrTG94SHlTakh6M0E/view?usp=sharing
it have 485, espo8266, expand port with i2s, ttl, ...
I also have some shileds caming
are we going to git this project?
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HKTarzan

Hi there to all on the forum,

I am a brand new member of your community (joined this morning) and are extremely interested and hopefully contributing to the OpenPLC effort.

I have a very strong background in hardware design, manufacturing, and maintenance.

I hope the forum is open to exchange of ideas to improve the product in the long run for all.

I am excited to see the 3D modeling and printing design work already done as a concept design.

I do however see one issue with the concept design as it stands now. In a "PLC" with say 8 cards plugged together, Murphy says that it shall be number card in slot number 4 or 5 that cause problems or needs to be replaced. That in itself is not a major issue, but I envisage a product that even a farmer in rural Africa can plug one card out and another one in... Is it not looking for trouble to ask unskilled labor to disassemble cards to get to a faulty unit??

I throw my 10c out there as I have started working on a design that shall have more of a Euro card-rack system design with cards plugging into a back plane...

The second question - Why not a 25pin Dtype in the front? That opens up more flexibility and options as you can go on the outside for solder, crimp and ribbon connector. In the developing world, you are more likely to find a 25 pin D type connector (Salvaged computer spares) than specific Phoenix connectors...

Let's hear viewpoints on theses issues

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r2k-in-the-vortex
D connectors are a nightmare(most people cant solder to save their hide), spring loaded phoenix connectors are definitely the way to go, good connection is pretty much guaranteed.
For PLC, the focus is not on serviceability, if you constantly need to service your electrical gear, you have failed already. PLC should be set up once and left well alone until the end of time. 
So the focus is on how to set it up right the first time.

Its a good idea to keep an eye on how modern industrial systems are designed. Card racks are history for a reason, D-connectors are half way there already.
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HKTarzan

Thiago, Petri

 

Is Petri doing the schematics & PCB layout or more focused on 3D enclosure issues? If the latter let's start discussions on the hardware and I am open doing schematic design and layout. The publish all back on here for evaluation.

r2k - I agree with your viewpoints and although Phoenix may be a tough one in developing countries, it shall still be the better connector for the purpose....

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Petri Mantere
I think that GIT is the right place for the design files when we are pass the concept phase. For now I rather use just A360 (Autodesk cloud) as it doesn't need much extra effort to make links to snapshots. You can download whole design also from A360, I won't put any restrictions on.

There are pros and cons in stacked design (no backplane). Main motivation not to use backplane is cost and flexibility. Backplane is more or less redundant part that doesn't serve any purpose, you can pass the same data from module to module. From maintanence point of view, back plane is a better design. You can also replace module to stacked design by splitting PLC and sliding both sides on the rail. Hopefully service life of the modules are long enough, that this is rarely needed.

D-connectors are designed mostly for low voltage/low current signals, so they are not very generic solution, although they will work in most cases. Phoenix connectors are the "correct" way to do interfacing.

I am focusing on enclosure. Also, help for 3D design is appreciated. For examble concept drawing for CPU-module is needed.
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