I am in the process of designing a Kosmo/5U variant of Europi. It’s mainly an exercise in trying to designing a module for both 5U (I started my adventure a few years ago in 5U) and Kosmo (I am very much in fond of Kosmo and the forum and it’s lovely people. It makes me hesitate to jump from 5U to Kosmo, but that is another topic).
The idea is that the pcb’s are usable in both formats, the panel of course not. Although I have thought of making a panel with v grooves or so that can be cracked to fit both formats, but it seemed a step to far…
I am relatively new to kicad and pcb manufacturing. I based my schematics on the published europi schematics and adapted here and there:
added JST connector for my personal 5U system
added opamp decoupling and termination of unused
added jumpers for selecting SDA/SCL order of OLED pinsocket
…
I was wondering if there are people out there interested in the idea of Kosmopi/Feifupi that could help me with some peer review of my adapted schematics. I have pointed out some questions in red text.
MCP6002 bypass capacitor should be 100 nF from pin 8 to ground.
In the original schematic no bypass caps are shown connecting to the TL074 power pins or the MCP6002, but (their) C3 to C6 are four 100 nF caps. I’d guess they are supposed to be the TL074 bypass caps, but none are provided for the MCP6002. Since you’ve added bypass caps to the TL074 power pins you can delete (your) C9 through C13.
D3 could be a 1N4148, but 1N5817 is okay too.
I don’t understand D4. Analogously to D1 and D2 it will protect pin 39 against a negative voltage on the +5 V rail but I don’t see how that would occur since the rail is directly from the +5 V regulator.
I don’t know if both ±12 V and ±15 V will work.
Unsolicited comments:
Here you have global symbols (the power rails) that connect to two different PCBs. That means in the PCB layout there are ratsnest lines from one PCB to another, which cannot be connected, and that means it’s impossible to avoid having unrouted connections. So KiCad cannot give you assurances that everything is routed that should be; if you have some other unrouted connection you might not realize it — if you try to use DRC (and you should) it will always fail. My suggestion is to use different power symbols for the different boards, e.g. GND on one board and GND1 on the other and so on.
A few points about this:
The reference for the MCP6002 (U5A??) isn’t shown here, you should go into the symbol properties and make it visible.
Comparing to the original schematic, U4C is connected wrong. It should be an inverting stage.
If the U4C stage is inverting then the MCP6002 output, and therefore its inverting input, is under +3.3 V as long as ANALOG_IN is under +15 V, so that’s good. But if ANALOG_IN is negative, the MCP6002 output will be negative, so the voltage at its inverting input will be out of spec. To protect the MCP I would add a 1N5817 from U4C pin 10 to ground.
Are these pots connected correctly? The arrow indicates they will go from +3.3 V at full counterclockwise to GND at full clockwise, which is likely wrong. However, it could end up being the reverse depending on which pot footprint you use — the KiCad library footprints do not have consistent pin numbering. If you’re using pot footprints with pin 1 clockwise and pin 3 counterclockwise (which evidently the original design used) then you probably should use a different pot symbol to be consistent.
I’d love to see additional pins for the screen so that those of us who don’t live in the UK can use the (admittedly cheaper and lower quality) generic screens rather than the (higher quality and longer lasting, but 4x more expensive) Winstar or PiHut screens.
Being a cheapskate, were it me, I’d try to see if i could cram it all on one fewer PCB haha.
Also, the screen is particularly small for 5U… I have not looked in depth at the code & how scary it’d be to port, but I wonder if it’d be possible to use a bigger one for a 5U conversion?
I have been checking this out. Good idea.
That said, there are cheap (ali&other) OLEDs with the same pinout and specs out there.
But I’ll try and take it as a beginner-exercise-challenge
My idea behind the separate pcb for the Pi was the following: The front panel&main pcb can be seen as ‘generic’. By designing another MCU pcb for another MCU (or even perfboarding) I can reuse the panel and main pcb… But you’re right, probably everything could fit on 2 pcb’s by puzzling along.
You’re right it looks odd, and there is room for bigger…
I am planning to stick to the ‘rules’ of the EurPi for now, so that the ‘programs’ out there need no changes. (no real programming skills here…)
Anybody any idea how to accomplish ‘free routing’ of the 4 pins of the OLED? There are a lot of possible combo’s… I guess that a patchbay style that needs manual wiring would be easiest?
If you do go with a bigger screen, I might be able to help with the code! I still have a few sets of PCBs of the original euro version ready to go so it’s probably just a matter of sourcing the display and rigging it up.
