1.0

[bstiq]

Todo

• add jumper for TRS on both sides

Updates

• added M4 holes
• added audio jack
• added I2C, SPI, matrix connectors
• added handedness resistor and jumper
• make usb-c reversible with the use of a daughterboard
• update pinout to be elite-pi compatible

[bstiq]

Turns out the pinout used in release 0.1c was not correct for miso/mosi/sclk.

On left: pinout used in the rev. On right: correct pinout.
This is fixed by d7908e2

[KarlK90]

Recommendations

1. ESD protection for USB-C port and split-comms port on data lines only or including cc lines (like shown)
   • protects against static discharge (charged cloths!) and subsequent destruction of any IC
   • recommendation StMicroelectronics (or knock-off manufacturer) USBLC6-2 in either SOT23-6L C7519 or the smaller SOT-666 C15999 package or the USBLC6-4 as shown

2. Schottky barrier diode in a larger package like SOD-123 C8598 or DO-214 C14996

   • higher sustained forward current possible and better heat dissipation
   • simple but not ideal due to voltage drop of 0.45V

3. Or ideal diode circuit which has nearly zero voltage drop

   • use a lmv321 which has a supply and input voltage range of +6V to not kill it by VBUS e.g. PJSEMI LMV321 C686637
   • a simple P Channel mosfet will do like AO3401A C15127
   • this circuit had problems when using op-amps that had a less then optimal voltage range, but works reliably with suitable op-amps as proven by YEAMK and Djinn keebs

4. Use a resetable fuse with a higher hold current like 1A (or higher if you want to support that) if you go with the ideal diode or a bigger Schottky barrier diode

5. Support full-duplex serial on the TRRS jack

   • much higher baudrates are possible, which in turn shortens the time to send data across the halfs. Thus frees up processing power
   • the kids want it :P

6. Expose SWD debugging headers, great for devs like me :-). The following signals need to broken out, preferably as a 2.54mm pinheader (3 or 4 pin)

   • SWCLK
   • SWD
   • GND
   • 3.3V (optional, but usefull if available)

[bstiq]

On a note -
It looks like this project is going to take more time than expected.
It is a bit less urgent right now thanks to plut0nium's excellent work on the splinky.

On top of those propositions, it'd be nice to move one of the matrix connectors on top of the other, so they align in a single line just like on the PCBs. This would make cable soldering and hotswap easier - avoid bending the cables too much.

It means probably rerouting a lot of parts on the board

Very rough POC:

One thing - be careful about daughterboard position - ribbon cables shouldn't collide with it