Tulip board next revision (and onwards) notes

[bwhitman]

I'm starting to plan for rev7 of the integrated board. I have an eye towards making the integrated board a thing you can order on a full assembly place like JLPCB or Aisler. The board can use some cleanup too, better routing, better BOM selection.

The goals are still that the board can't do anything a breadboard or breakout board can't do: that means, no special features that can't be done in DIY through hole or on a breadboard. All of this below can be done just as easily with a breadboard and/or breakout boards:

Potential board changes:

• removing or replacing the 6N137S with something much smaller to save space
• fixing the USB-C connector to bridge DP2 and DN2 to DP1 and DN1
• using a different FPC connector for an A-A cable, or moving the existing one to the back side
• moving the USB-A connector for keyboard to USB-C to save space
• removing the header on the left side and:
  • replacing the 5V_USB, 5V_IN, GND headers with a single JST-3 connector for external battery charger
  • using a small 2-position DIP switch for power input selection
  • removing the I2C connectors until we find a use for them
• Cleaning the BOM enough that a board assembly place can build it without external parts shipped to them

And potential new features:

• An optional header for a VGA connector, on the back, behind the FPC40 connector. This would allow (I believe) 255-ish colors at 640x480 at 72Hz (or, to keep the ratio, 800x480 @ 60Hz?). I'd have to add resistors somehow for the ladder without getting in the way of the RGB TTL display. I have to do a lot of testing for this before I confirm it's even possible, but it does look straightforward to use our "GPU" code to generate VGA signals.
• An optional header for a clock/data/latch NES/SNES style controller. These are massive connectors, though, and I'm not certain the best way to place one on the board. Maybe along the right side, underneath the audio & MIDI jacks. Or, just expose them as 0.1" header pins and let people build their own adapters. We would then add an API for tulip.joy() which would return a 16-bit mask of buttons.

Rev8 onwards ideas:

• charge & boost on board
• power button (putting Tulip in low power / out of low-power, like Alles) instead of power switch
• real routing (i'd love help from the community here!), and a port to KiCad from Eagle

[bwhitman]

Re: joystick - I found that the MiSTER people have a good spec around "SNAC", which basically converts the necessary pins on many types of controllers to HDMI or USB3 ports. I could put a USB3-A female jack on the board and anyone that wants to use an NES or SNES controller can buy a cheap SNAC adapter.
Here's what one of those converters looks like as a board -- it's really just changing the port type and mapping each SNES pin to a USB-A connector pin.

Not a bad idea -- certainly will be confusing to those who aren't "in the know", but does help keep the board size down without me having to design / sell my own adapter. And for breadboard & breakout tulip, the pins will just be there for a normal DIY SNES connector if they want it.

[bwhitman]

I'm getting closer on r7 -- eagle files are in the repo now.

I've decided to just have pins broken out for an SNES connector (and i've wired this up in the firmware, see tulip.joy()). This would be an optional part, alongside the bottom underneath the board.

I've swapped out the 6N137 with a VO0601T.

I've flipped the FPC connector so it takes normal A-A cables, like the one in the display.

I've removed the pin header. You now just jumper a smaller 3-pin header for power selection. There's now a JST connector on the side for battery.

[bwhitman]

Here's the OSH render. One nice feature of this board is all extra ESP pins are now broken out / accessible via through hole if you want. If you're not using the joystick, there's 6 usable GPIOs available, plus the I2C bus.

I've moved the FPC connector to the back and am using a "reversed" part so that the cable that comes with the display will attach from the bottom and not need to be flipped if used in a laptop-like hinge setup.

I've fixed the USBC connector and updated the silkscreen for the RESET and diode.

[bwhitman]

Got r7 booted today!

I love the new battery JST connector, makes things easier. I don't love the optional SNES controller port on the bottom as it doesn't fit my custom case that well. I don't think it's an issue.

The new FPC connector is easier to install as it's not too close to anything on the back. And it's a "back locking" type which feels more solid than the last part.

I still screwed up my USBC connector assembly, so I can't yet confirm our changes to the USBC pins are working. But they should!

[bwhitman]

Some light notes for r8:

• AGND & GND planes -- we have some noise coming through the DAC when charging an external battery
• move the SNES controller port to the top front -- the bottom placement is too annoying for a case
• move to a through hole power switch -- the SMT one is $$$, and is very hard to solder on! and it's big
• move JST external power pins to 5V_USB, GND, 5V_IN so they match "standard" yellow/black/red cables
• swap the ext-usb jumper around so it's easier to put on the jumper

[bwhitman]

I submitted r8 with all those changes except the JST swap -- i like to keep GND on the edge so the board doesn't burn out when it's inverted. I also removed the jumper in favor of a switch. Looks good!