BOM, cable wiring, improved silkscreen

[danboid]

I'm interested in building one of these boards but it needs a bit more documentation.

Could you please add a BOM to the repo? It seems there is a mostly complete BOM here:

https://oshpark.com/shared_projects/aK2wBkfg

but it is missing designators for the parts - its mainly U1, U2 and U3 and J3 that I'm unsure of.

I would also need a pinout diagram showing how to wire J2 up to a cable.

It would be good to see the silkscreen improved to show the button wiring on the PCB and adding a photo of a populated, wired board to the README.

Thanks

[rfmerrill]

I agree all of these things would be nice and would happily accept a pull request that added them!

[rfmerrill]

All of the information you need is in the KiCAD project, but I didn't include a schematic print in the repo which is actually a pet peeve of mine when other people do it. Unfortunately it's been so long that I don't think I even have KiCAD installed anymore.

but it is missing designators for the parts - its mainly U1, U2 and U3 and J3 that I'm unsure of.

It should be obvious which footprint is the microcontroller and which are the two multiplexers because they have different pin counts. I believe U2 is the microcontroller.

J3 is a standard 2x3 IDC header, which I think will mate with either the USBtinyISP or the Atmel ICE's AVR adapter pigtail. If you just search for "2x3 IDC socket" pretty much any of them will work as long as you get one with the common 0.1" pin pitch.

I would also need a pinout diagram showing how to wire J2 up to a cable.

Ah I feel bad that I didn't include this because I don't even remember! I want to believe that I was a good boy and used the same pin numbering as the joystick connector itself, but I cannot guarantee that I did, unfortunately.

It would be good to see the silkscreen improved to show the button wiring on the PCB and adding a photo of a populated, wired board to the README.

Agree, and these seem like easy tasks for someone to do :)

[danboid]

J3 is a standard 2x3 IDC header, which I think will mate with either the USBtinyISP or the Atmel ICE's AVR adapter pigtail. If you just search for "2x3 IDC socket" pretty much any of them will work as long as you get one with the common 0.1" pin pitch.

That's what I guessed it was but its good to have confirmation.

Ah I feel bad that I didn't include this because I don't even remember! I want to believe that I was a good boy and used the same pin numbering as the joystick connector itself, but I cannot guarantee that I did, unfortunately.

Oh dear!

I have attached what I believe to be the standard Atari joystick pinout so hopefully you've used that, one way or the other. It would be a bit strange if you haven't laid them out in this order or its reverse.

I would presume that the square pad on J2 is for pin 1 on that Atari joystick port diagram?

It would be good to see the silkscreen improved to show the button wiring on the PCB and adding a photo of a populated, wired board to the README.

Agree, and these seem like easy tasks for someone to do :)

If I build one I'll fix your docs, yes.

Would you recommend that we use the gerbers from the latest commit or the tested version?

[rfmerrill]

OK, I have been able to confirm that I was in fact a good boy and J2's pin numbering matches the joystick plug. Note: that pinout diagram you posted reflects the socket--the plug is mirrored from that. Also those pinout descriptions are for the actual atari consoles, but we only care about the pin numbers in this case. And yes, square pad is pin 1

Here is a photo of one of the boards I assembled that I was able to dig up:

Please ignore the wire colors as while Sega may have been consistent, third parties definitely were not.

There are a handful of minor mods here--points to clip to for supply voltage, an extra capacitor (don't remember why, probably not needed) and a jumper wire that allows for supporting 3-button mode (hold down MODE on powerup--requires the firmware from main).

You'll also notice I just used 2-row pin headers instead of IDC. This is also fine it just means you lose the keying and have to pay attention to pin 1.

Would you recommend that we use the gerbers from the latest commit or the tested version?

Ah, there are not actually any gerbers here as I relied on OSH Park directly accepting kicad projects... I don't remember what changed from the tested version to the latest commit. Tested version is probably safer I assume.

[rfmerrill]

And no, that's not hot glue, it's RapidFix UV resin. I don't own a hot glue gun.

[danboid]

OK, I have been able to confirm that I was in fact a good boy and J2's pin numbering matches the joystick plug. Note: that pinout diagram you posted reflects the socket--the plug is mirrored from that. Also those pinout descriptions are for the actual atari consoles, but we only care about the pin numbers in this case. And yes, square pad is pin 1

Very useful info that.

There are a handful of minor mods here--points to clip to for supply voltage, an extra capacitor (don't remember why, probably not needed) and a jumper wire that allows for supporting 3-button mode (hold down MODE on powerup--requires the firmware from main).

Thanks for posting a pic of the board but what is that big ugly blue bodge wire of doom about? Brudda ewww! Will have have to add that to get it working?

Not sure I'm bothered about the MODE button. I'm actually building this for use with the ZX Spectrum Next rather than the MD. I owned a MD 30+ years ago and I'm tempted to buy another and a flash cart but I'd probably not use it enough to justify buying one.

[danboid]

Would I need to add those wires from U1 to C1 too? That doesn't look good or fun to do.

[rfmerrill]

Thanks for posting a pic of the board but what is that big ugly blue bodge wire of doom about? Brudda ewww! Will have have to add that to get it working?

I answered that in the comment you've replied to, it's to enable 3-button mode. Also I thought I did a pretty good job with it... how would you have done it?

Not sure I'm bothered about the MODE button. I'm actually building this for use with the ZX Spectrum Next rather than the MD. I owned a MD 30+ years ago and I'm tempted to buy another and a flash cart but I'd probably not use it enough to justify buying one.

Er, ok, I know nothing about the ZX Spectrum Next but I have not tested this board with anything but an actual mega drive. I would guess if it supports 6-button mega drive controllers, it probably doesn't need the override for 3-button mode so you can use the release version of the firmware and ignore the jumper wire.

[rfmerrill]

Would I need to add those wires from U1 to C1 too? That doesn't look good or fun to do.

No I just did that so I had a convenient place to connect a scope or bench power supply to the power rail. There are other ways to achieve that if you need to, and I don't know if you need to (only reason I can think of is in case you can't power the board through the programming header, but I think you can)

[danboid]

OK, sounds good.

If I can get the firmware to build I'll probably have a go at building one of these. Pretty sure you didn't upload the .hex file for the MCU to the github right? I should have no problem building it myself, I've Arduino'd before.

Thanks!

[rfmerrill]

Yeah if you can still install Atmel Studio (I think it's called Microchip Studio now?) it should just build. Just have to make sure you install the 8-bit AVR toolchain with it.

[danboid]

Final question today / tonight is have you ever heard of the open source 8 bit Uzebox games console before I started bombarding you? Its the fastest, cheapest, most open and easiest to build 8 bit console platform, if any of that appeals to you?

https://uzebox.org/

I recently helped create the joystick for the Uzebox and wanted more of the same for the ZXN.

[rfmerrill]

maybe someday, my time is mostly taken up with work and guitar practice these days. I'm sure I'll get back into gaming sometime!

[danboid]

Guitar practice is definitely a better use of your time than playing games IMO. I find trying to write games more fun than playing them.

I support the Uzebox because I think we need a fully open retro platform and its a great project for people learning electronics to get started with. Same goes for the Spectrum Next. They compliment each other well.

[danboid]

I'm hoping to make a start on building this soon. I've still not even tried building the code yet.

I'll most likely use the latest revision but with extra info added to the silkscreen.

How do you want to be credited on the silkscreen? R.F. Merrill?

RF makes me think Robert Fripp. Do you like King Crimson?