This is an adapter for plugging full-size HATs into a Raspberry Pi 400. The commonly recommended way to plug GPIO adapters onto a Pi 400 is to use a male-female extension cable - it's a flimsy connection, it's not mechanically solid and it doesn't look as good. This adapter will give you a solid connection and hold your HAT parallel to the Pi 400 keyboard - with some useful connectors added, too!

Fixes in v2:

• You now have 50% chance of receiving a PCB with a dragon clipart on it. If you order more than 1pcs in the same order, you're likely to get one adapter in a "dragon" version - also known as "V2d" ;-P. If you really want a PCB with a dragon on it (i.e. gift for a kid), let me know in a message while placing the order and I can see if I can make that happen, this will have priority over the "2pcs" thing. If you're wondering why the "dragon" option is there, msg me on Tindie and I can explain =)
• Changed mounting holes to M3 so drilling is no longer necessary to use widely-available M3 mounting hardware
• Moved the 5-pin I2C connector to be flush to the board edge
• Fixed small routing mistakes

When I looked at Pi 400, I noticed - the GPIO header placement isn't very well-thought-out and feels more like an afterthought than anything. Ideally, the GPIO header pins would be available on top of the case, and everybody would be able to continue using the HATs as they did before - plug a HAT on top of your Pi and do whatever you want. However, the GPIO connector's placement is awkward, and the common suggestion is to use an adapter cable - that's just not as practical. This is the perfect addon for your Raspberry Pi 400 if you want to play with HATs comfortably.

I've worked with Raspberry Pi boards for a long time, in educational, embedded and recreational contexts, and I know the features that an average Pi user wants. This isn't just a sturdy GPIO-to-HAT adapter with a lot of care put into its design, I've added features and quality-of-life improvements to it, too.

Extra features:

• Two QWIIC connectors (STEMMA QT compatible) for all your I2C devices you might've gotten from Adafruit/Sparkfun
• A Pi-compatible I2C connector for basic devices that has an extra GPIO. It lets you add any extra sensors with just Dupont prototyping wires - and if you have a HAT with I2C devices on it that plugs onto a Pi, chances are, this connector will let you run it without even occupying the main GPIO header with it.
• A 12-pin connector with SPI, I2S, 3.3V and 5V on it. This allows you to connect SPI sensors to your Pi even easier than before - whether it's an Arduino, a MCP3008 ADC board or a laptop SPI BIOS chip in case you want to make your BIOS a bit more free. SPI CS is connected to CS1 pin - to avoid conflicts with HATs that use SPI; it's easy to remap using a solder jumper in the corner of the board. The I2S pins can normally be used as 4 GPIOs, but also allow you to tinker with I2S audio chips, letting you in on an underappreciated way to add microphones and audio outputs to your Pi on the cheap.
• Mounting holes and standoffs - to firmly hold the HAT in place without any disconnections or flexing. The mounting holes are spaced in the same way they are on a Pi, and there's 2 standoffs included in the kit that you can attach to the board for extra stability.
• Onboard pinout description for 5-pin, 12-pin and QWIIC headers - no need to consult any pinout diagrams for the Pi if you just want to connect a sensor quickly and get to writing software.
• SPI and I2S clock lines on the side header have a 47R resistor in-line - to reduce any ringing and make high-speed SPI connections work better.

One thing I wish I added but couldn't is a Raspberry Pi GPIO pinout silkscreened right on the PCB - it will be present on the boards from the next batch. Unfortunately, due to awkward orientation of the Raspberry Pi 400 GPIO header, it wasn't possible to use a 2-layer PCB for this adapter, so I had to go for more expensive 4-layer PCBs, otherwise this adapter would be even cheaper.

Oh, also - I have a small stock of cute SPI chip adapter boards - for reprogramming laptop BIOS chips and the like. Their pinout is compatible with the 12-pin header, and I've tested them to work with flashrom (through this adapter, of course). You can adopt one of these boards for the low low price of $1.50!

Package contents

• One adapter PCB
• Two screws
• Two HAT standoffs