Raspberry Pi GPIO Breakout Hat

[Andy-ABTec]

Further to my adventures with OctoPrint, GPIO filtering, the Micro Panel, Emergency Stop switches, relay control and the like it soon became evident that some form of "breakout hat" was needed. Additionally, my particular situation was complicated by the fact that I use PoE hats on my Pi's and needed to squeeze an additional board in between the Pi itself and the PoE hat. Sort of like a Raspberry (Pi) sandwich - sorry!

To be more specific, looking at the bird's nest growing around my "test" Pi, I needed to provide access to the I²C bus, the UART and a selection of filtered GPIO pins for both active high and active low input as well as some GPIO, ground and supply (3V or 5V) pins for the cheap relay boards available.

With that functionality in mind, I trundled off to Gadgetoid's excellent Raspberry Pi Pinout Guide looking for details of the Pi's 40 pin header.

Armed with this data it was time for a schematic...

Being fairly fluent in Fusion 360 (Personal License) I thought I'd try Fusion Electronics...

Once over the initial almost vertical learning curve, I managed to create the circuit above with I²C bus, UART outputs on 4 pin headers, six filtered GPIO inputs on 2 pin headers, configured active high or low with jumpers, and four GPIO outputs on 3 pin headers with earth and jumpered 3.3/5V supplies suitable for driving relay boards. All without touching any of the "pre-defined" GPIO pins.

With SMD components and low profile jumpers, it should be possible to shoehorn everything onto a Pi Hat.

After a few hours searching on the internet, I located a supplier for the 40 pin SMD header sockets favoured in the manufacturers of Hats for Pi's that would allow my needed passthrough connectivity to the GPIO.

Armed with my circuit and the good fortune of finding the connector I set about the board design.

It's amazing how quickly you can fall out with a piece of software...

Having been lulled into a false sense of security with Fusion's schematic offering I was gobsmacked by the Layout "editor" - frighteningly quirky and unintuitive was an understatement, and after three days of trying to create the 40 pin SMD socket in the Library, I eventually got the white flag out and surrendered.

What little documentation I could find was great at "Hey this is how you use the handy-dandy package generator" but when it came to designing something totally new (that the package generator couldn't handle) from the ground up what I found was either nonexistent or appeared to be apocryphal, or at least wildly inaccurate.

So there we are, I'm stuck bigtime by the lack of information/documentation - if there's anyone out there who can help me create a Library entry from nothing please get in touch before I'm totally bald and my project is in the bin!

[Andy-ABTec]

@sethvoltz, I guess from #49 (comment) I need to add a couple of 4K7's to the schematic (yes, I'm still working on it), can't do any harm for them to be here all the time...