misteryshield20k_rpipico_dual_db9

[Manger74]

@vossstef

Recently I had an idea for a shield variant, based on your misteryshield20k_rpipico...

What i have in mind would be the following modifications:

remove: MIDI sockets and circuitry, spare pin header, debug header

add: 2nd DB9 port, USB-C power only receptacle, a pin header for a power switch

Is it allowed to fork and modify your design? If yes, I would like to ask you for some support and feedback! I'm new to hardware design and i'm not sure if i can get everything right...

[Manger74]

Had a conversation with ChatGPT about a power circuit for the shield variant...
Is this usable?

[vossstef]

@Mangerrione (@harbaum ) would like to keep the existing Board with MIDI Interface.
If you want to create a new one then better store it under another dedicated name e.g. misteryshield20k_rpipico_tbd in the Boards folder

I personally use other circuits as reference rather than ChatGPT fariytale. e.g. https://dl.sipeed.com/shareURL/TANG might be of interest

[Manger74]

@vossstef

Sure! It was never my intention to modify your board, I was planning to create a new variant based on your design!
So i will upload it under a new name!
Thanks!
It would be nice if you and Till could help me to check everything before i place a order at JLCPCB...
Thanks also for the link!

[Manger74]

Have uploaded my experiments under misteryshield20k_rpipico_dual_db9

The board is meant to be an option for users, who don't use Midi but like to play games a lot, including two player games... like many C64 and Amiga fellows...

the USB-C power port will allow to add a case power button, it should also save the TN20K's USB-C port from wearout and could be used for a USB-C thumbdrive in the future...

for me this ist a way of learning KiCad by doing...
i'd like to develop the skills to design a custom board for my "NanoBox" case!

I hope you experts can help me a little to get it right!
find the flaws and find ideas for improvement...
Many thanks in advance!

[vossstef]

@Mangerrione pls. share the circuit diagram when ready. Sorry but can't comment on PCB Layout aspects

[Manger74]

@vossstef Thank you for reviewing the schematics! Have uploaded the circuit diagram as PDF. I think the 2nd DB9 port should be okay, nothing fancy there. The board power circuit i have designed with the help of AI. Please let me know if this is crap. Then i will find a better solution and rework it. I'd like to have a power button to prevent wearout with the USB-C connectors. Maybe the pinheader is not the best solution? Please let me know if you find flaws or have ideas for improvement! Please take your time, no hurry! Happy weekend!

[vossstef]

@Mangerrione circuit looks at a glance fine. Pls. ensure to align the componnet size and types. Means R28, R29 as 0805 package. change C11 to 0805 size and e.g. order code C49678, the 22uF also as 0805 and e.g. order code C45783. The fuse best to be a self resettable type e.g. PTC RESET FUSE 6V 2A 0805

if you want to connect an external switch then a 2.0 or 2.54mm pinheader might be a good choice as it can be jumpered to closed if feature not needed. at the moment circuit diagram shows both header leads connected and need a rework.

[Manger74]

@vossstef
@harbaum

The three LED's for Keyboard, Mouse & Joystick are nice!
You can see instantly, if your inputdevice is recognized...
I would like to add a LED for drive activity...
And Power + Core Ready eventually...
Power is easy, could be hardwired to +V3.3
But which LED's indicate Drive Activity & Core Ready?

[harbaum]

I think your TVS diode is the wrong way around, if it's really a unidirectional one. Currently, it will IMHO just conduct and create a short.

Edit: ... and it's a 5.0V diode which means that it clamps to 5.0V which may not be what you want if e.g. your Power supply delivers e.g. 5.1V ...

See e.g. https://solutions.mccsemi.com/understanding-tvs-diodes-a-comprehensive-guide

[Manger74]

Thank you for your feedback!
Have fixed the orientation.

The TN20K and the PiPico expect +5V +/- 10% then the clamping voltage should be around 5.5V or 6V?
Unidirectional is okay? What other specs are required?
Could you please help me to select a part that fits the requirements?
https://jlcpcb.com/parts/2nd/Circuit_Protection/ESD_and_Surge_Protection_(TVS_ESD)_3035

Is the fuse okay with 6V 2A?
https://jlcpcb.com/parts/componentSearch?searchTxt=C70158

If the fuse and the surge protection are okay, the rest of the board should be fine!

[harbaum]

I think 5.5V should be fine, as the devices should tolerate +10% in the supply voltage.

I don't have much experience with these, and I don't think it's super critical. If it doesn't work you can just remove it and the device will still work.

[Manger74]

This is what i have in mind about the LEDs...
analogue to MiST and MiSTer...
to make it work, we would have to standardize the two signals for
Core and Drive Activity so all cores would give the right signals...

[harbaum]

Yeah, why not. But I would not enforce this. There are so many shields now that I wouldn't design the cores for a specific one.

The Amiga e.g. has a core controlled power led and multiple floppy drives and HDDs and someone might want to use all LEDs of the tn20k for this. Also, sometimes the LEDs are used during development for debugging.

[Manger74]

If i understand it right, LED#1 signals that the Core is up and running on the NanoMig and #2 is Floppy activity? #3 is HDD1 activity? For the "NanoBox" i would like to have two case LEDs on the custom PCB. Power & Activity. I intend to experiment a little with the LEDs. So i will order this PCB with the extra LEDs for my personal use. If you wish, i can remove em for the MiSTle project page afterwards...