Using Pi-Hats together with a Pico

I own quite a number of Pi-Hats and wondered if I could reuse them with a Pico/Pico-W. So I created two adapter PCBs: “pico-zero-base” and “pico-pi-base”:

This is not something like a “poor man’s pi”: some hats are just better suited for the Pico because the Pico doesn’t take have a minute to boot and does not need a clean shutdown. And you don’t want to by an expensive Pi just to use the Scroll pHat to display some scrolling text ;-)

There were a number of challenges in the project:

  • pin-mapping: both boards now support I2C, SPI, UART and I2S
  • form-factor: the PCBs have Pi-Zero and Pi format, this they fit into available cases
  • layout: I wanted to keep the area underneath the WLAN-chip and antenna without traces
  • software

Porting the Linux-drivers of various hats to the pico was easier than expected, since most of my Hats had python-based drivers using I2C or SPI. So I only had to change some lines of codes, mainly the low-level I2C/SPI-functions. And since I am a CircuitPython user I could rely on 400+ libs for all kind of components, this also makes live easier (but MicroPython shouldn’t be much more complicated, it only takes longer searching for and installing software).

Currently I ported/tested the following Hats successfully:

  • Scroll pHat HD
  • Touch pHat
  • 4-Letter pHat
  • LED-Shim
  • Button-Shim
  • Pirate-Audio Speaker-Hat
  • Pirate-Audio Shim
  • Adafruit Speaker Bonnet
  • Display-Otron-Hat
  • InkyImpression 5.7"

You can find all relevant information here: GitHub - bablokb/pcb-pico-pi-base: An Interface PCB to use Pi-Hats with a Pi-Pico(w) (including ready to order production files). PCB-production is very cheap these days, a batch of 5 of the pico-zero-base costs about 6 Euros (including tracked shipping and EU-taxes). The pico-pi-base is a bit more expensive (16€/5units), mainly due to the higher weight. The only thing you have to solder are the Picos and the pin-headers.


I like your thinking, and bonus for actually building an actual board. =)

You have been busy. What a great project.

I’d be happy to pay a commercial price for these boards as a kit/partly built. I hope someone will put them into production and make them available.

It is all open-hardware, so in theory anyone could build and sell them. But things get more complicated if you sell: you would also have to provide support.

Besides this, it is also a price issue. If I order a batch of pico-zero-base in China, five pieces will cost less than alone the shipping I pay when I order something from Pimoroni. But it is probably as you said: some people would be willing to pay a commercial price.

@bablokb I just found this project and am likely going to get some pico-pi-base boards produced…

I did notice that the rst switch was not included in the assembly BOM. Shouldn’t be any problem finding the switch and installing it myself, but was wondering if there was a reason it was not part of the assembly. Not available from LCSC?

Thank you for a great design and project!

For info…
If you are looking for a “ready made” PICO pretending to be a “regular Pi” solution there is a board called Pi-Square made by SB-Components. The PCB has an embedded PICO RP2040 chip with added ESP module for WiFi and a small monochrome OLED display. It costs £20.

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Yes, I didn’t find a suitable switch from LCSC. Buttons and switches are labelled in a way that their search does not turn up everything. I think I now found some, so I could revise the board. But I do have enough of them, so this is not a priority on my list.

Finding the switch yourself might be difficult, since it must fit exactly into the holes on the pcb. And to be honest, soldering them was a real challenge, they are very very small.

The pi-zero-base is simpler. Pimoroni has these THT switches.

Thanks for the link. Not a bad product and well documented. But since it does not support the Pico-W, you have to adapt all your network programming and route your stuff through the co-processor. I actually use a similar ESP-01S together with a normal Pico and that works very well unless you need https. So this should not hold you off.

The SB-board has one problem: it won’t support I2S (wrong routing of pins), so various audio-hats won’t work. But they don’t claim that, so this is ok. And audio from the Pico is not high-quality anyhow.

Further info…
Just had a notification of new stuff on Aliexpress including an interesting version of a Pi-Zero (non-wifi) development board using an RP2040 “engine” which includes a Micro-SD slot, mini-HDMI socket and two USB-C sockets. There’s no camera but there is lithium battery support.
It’s actually made by Waveshare and Aliexpress costs £8.55 inc and Waveshare $9.99 exc.