Expansion Headers

There are 4 expansion headers on the board, each carrying 2 data pins, 3.3V, and Ground, and they can each be used with essentially 3 different protocols.

The first, and in my opinion the most useful, is I2C. I like this protocol, because there are already so many expansion and sensor boards for it, so it would take very little effort (nothing more than mounting one behind a panel and connecting it at the back) to add for example a display, or even a fully fledged audio processor to the EuroPi, and have your program control it.

The second protocol is UART. This one will potentially allow external USB expansions, so think USB MIDI to CV, or even syncing your rack to your DAW.

The third is plain old GPIO. You could use the two data pins as two separate channels, either digital, PWM, or filtered PWM (faux analogue).

The headers use 2mm pitch, rather than the 2.54 (0.1") headers found elsewhere on the board. This isn't just a space saving tactic, it allows the standard JST PH connectors that come pre-wired on many I2C devices to be connected right out of the box.

Although there are 4 headers, the Pico is only capable of 2 I2C and 2 UART channels simultaneously, so you will have to pick the expansions carefully (although if your I2C devices all use different addresses then you could potentially have up to 127 connected). Unfortunately this hardware limitation is one of the downsides of keeping the project so affordable.