BasicPI

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I admit it sounds a bit ludicrous, but right now I miss an source code aware sort function in my IDE. If you start maintaining large files with loads of structures or functions you often end up paging up/down looking for them – to reduce this time I start sorting them in alphabetic order.

enum vm_OpCode
{
 Op_Assign=1,
 Op_Call=2,
 Op_Commit=3,
 Op_End=4,
 Op_Exit=5,
 Op_For=6,
 Op_If=7,
 Op_NOP =8,
 Op_On=9,
 Op_Raise=10,
 Op_Rollback=11,
 Op_Spawn=12,
 Op_State=13,
 Op_Switch=14,
 Op_Transaction=15,
 Op_Update=16,
 Op_While=17,
};

The struct above is another example – I sorted it to easier keep things synchronized – doing so is actually an increase in quality because it means the developer uses less time looking for things and get a better overview faster – each of these also have structs, execute functions etc.

Nice to see CH340G finally registering correct on Windows. The circuit below works just fine.

The first you always should do is to measure if you have power – in this case 3.3V – I actually did, but as I finally measured on the pins I noticed that I actually did not. Looking at my schematics (and routing) I realized that I had connected the circuit to the wrong 3.3V that I had not assembled yet – doh…

It is an annoying error and even more annoying that I did not see it straight up. The real problem here is that I have made it difficult for myself not providing test points on a rather complex board . But, I am very happy to see this working as expected.

The last I need is yet another board without code, but I like to draft some PLC boards. This is a com adapter connecting the backbone to Ethernet and external RS-X lines. The code will be a variant of what I will make for the com adapter.

Just updated the pin numbers on the PLC Backbone Bus. The idea here is that we have 4x RS-X lines (2 optional) and 5V,12V,24V,48V supplied from A and B source. The boards select what power they need. I need to connect to a PSU & battery before I am sure that this is what I want to do.

48V is mostly for higher motor effects. 24V & 12V are quite handy to have around, while 5V is an absolute requirement – thought I might actually ditch 5V and supply a separate 12V for MCU expecting the boards to regulate 5V/3.3V themselves. The idea of having a separate MCU power is to avoid the need for galvanic isolation as any effects are drawn from separate power lines.

This is just an early 3D model of the minimum backbone bus just to illustrate and work on practical issues. I am going for the more minimal bus for now. The size of the bus do not decide the size of the boards, but I do like this small size. I will however adjust the actual size to practical applications.

What is missing here is a better way of interconnecting several boards and connecting to the PSU. But, I am happy with the PSU lanes – I had no problem using 2mm wide lanes on each side for GND,12V,24V,48V on both A and B. Simply said we can handle some currents in the backbone.

I added 8 slots expecting that we will use 4, but I also miss mechanical fittings of the IO boards here – as I plug IO boards in I need a mechanism to hold them in place.

It is several design considerations that is not solved yet – vibration, interconnection between boards, fixing of sub-boards, connection to RS-X networks etc. But, we need to start somewhere.

The previous proposal included a lot of data/address/function pins that actually is a bit obsolete design as we use multiple RS-X channels. This smaller bus uses 2×20. I can use the same width as for a Hat, but maybe a bit deeper boards.

I need the PLC system to be small and mobile to fit robots. I wanted a wider system to get more connector space, but I can add 2nd slots for those few cases. In short – I feel that increasing the size would be a mistake.

It is an alternative – and I could even do both …

If I use a 10cm wide backbone I have room for a 2×30 (or 3×30) by 2.54 pitch “bus” that could contain the following Inventory:

Summarised this gives me:

• 4 pin 5V PSU (5-10A)
• 4 pin 12V PSU (5-10A)
• 4 pin 24V PSU (5-10A)
• 4 pin 48V PSU (5-10A)
• 4 pin GND 5V
• 4 pin GND 12,24,48
• 8 pin data bus
• 12 address bus
• 10 function/extra address pins
• 8 pin for 4 RS-X lines (RS485)
• 2 clock pins

This is just a working draft…

The more I look for any real standards within PLC the more I get the impression that they either do not exist or is not used. This is consistent with what automation engineers tell me. I was kind of getting my hopes up with “Industry 4.0”, but well… lets crack on with creating our own.

The first PLC module I want to make is a box that can hold Raspberry PI + 1 or 2 Hat’s. Having the capability to add a RPI 3 or RPI Zero W is a great asset. It also provide a solution for industrial mounting of a RPI.

This enables 4 PLC modules “as is”:

• Linux/Windows computing module
• 5 port RS485/CAN communication Gateway
• 16 channel Servo/IO
• 8 channel DC Motor, 8 channel Servo/IO

I will create more Hat’s so they can be added as PLC modules as well. I am a bit wage on the details around how to integrate Raspberry PI itself. I want PLC connectors in front and that leaves Ethernet + USB at bottom. The more problematic side is accessing the backbone – suggestions are most welcome.