Author Topic: For Your Amusement.  (Read 2678 times)

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Offline anathae

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  • Location: Edmonton, Alberta, Canada
For Your Amusement.
« on: Thu, 21 September 2023, 18:41:46 »
Attached (I hope,) is a screen shot capture of a PCB created in KiCAD using a foot print I've created for the Raspberry Pi Pico W board and a close up of the foot print in the design.  This is as an example of why I made it, and why I think other people making stuff with this MCB (Micro Controller Board) might find it helpful.

I love the Pico and Pico W.  Unfortunately, they have the dreaded USB Micro port on them.  It is my understanding that this is REALLY bad.  Most of the replacements by other companies are usually more expensive by a fair amount.  Doesn't hurt that I was able to get four of each shortly after they were announce as available.

The Pico W, as the heart of a blue tooth mechanical keyboard seems like just the thing.  $7.95 CAD for a board with lots of IO (maybe for a full size keyboard matrix?) and blue tooth LE and Classic.

Disadvantages... Micro connection that is tightly coupled with the board foot print, no battery charging.

Solutions:  Both MCBs have test point foot prints on the bottom side for for USB D+/-, as well as for the boot switch.  two more are down there, but documentation says, don't use them or that they don't recommend using them, and I am agreeing with that.  I have added a plated through hole under the USB D+/- and associated ground (TP1, TP2, and TP3) as well as under the boot switch test pad (TP6).  In my example numeric keypad, I have cribbed the components from the Pimoroni Pico Lipo Shim.  I hope they don't mind, and this way I can adjust the charge current from 220 mA, to 150 mA, with out having to rework the shim.  Others may decide to use the shim in similar way to how I'm using the Pico W.

Design choices.  The PCB for the keypad is intended to plug into the PCB for the MCB.  for the purposes of testing, however, I have wired up the 2x5 connectors on the two boards such that with out breaking them apart, the total thing could be assembled and tested.  I'm using the Kailh hot swap MX style key sockets.  Testing out different types of mechanical Cherry MX style key switches might be in my future.  My foot print for the Pico W includes a 14mm by 14mm keep out area for the cavity antenna.  Raspberry Pi Pico design documentation calls this a 9mm by 14mm area.  The foot print keep out I've put in is centered between the two rows of pins and used the 9mm measurement to line up on the end of the Pico W board.

Future directions.  The traces for all the switch diodes are actually on the bottom side of the board, as are the key sockets, I might "upgrade" from DO-35 through hole 1N4148 diodes to a surface mount diodes.  There is enough space on the controller to add a small prototyping area to one side, especially if I move the MCB over from it's current central location on the board.  The three pins for the SWD port on the MCB have not been added in this version of the foot print.  Might change that, as this is a Pico W with out header version of the foot print, not a Pico W or Pico with out W foot print.


KiCAD files may become available, if anyone is interested.;