Pimoroni’s pHAT Stack (£14/$16) enables you to use multiple add-on boards simultaneously with your Raspberry Pi.

Also available as a solder-yourself kit (or just a PCB board), the Stack is equipped with five sets of 2×20 pin headers, plus one to connect to the Pi via a GPIO ribbon cable (supplied). This means there’s room to connect five smaller pHAT boards, three full-size HATs, or a mixture of both.

While this might seem like overkill, it provides a convenient way to switch in and out different HATs and pHATs and create your own custom combinations. So it’s ideal for experimenting with hardware project ideas.

One nice touch is that the three of the GPIO headers have their pins fully labelled, which should prove handy for connecting up your own circuits and sensors. Brass standoffs and screws are also supplied for secure mounting of HATs and pHATs.

Pimoroni pHAT Stack review

While it’s very easy to mount the add-on boards on the pHAT Stack, one caveat is that not all of them will play nicely with each other: you need to look out for those that use the same GPIO pins. Pimoroni’s ‘pHAT Stack configurator’ online tool comes in handy here: hosted at the ever useful pinout.xyz, it lets you simulate adding various HATs and pHATs to the Stack and will warn you of any pin conflicts. Multiple boards may still use the same I2C pins (BCM 2 and 3) without issues, so long as they use different addresses.

In our test setup, we combined a Speaker pHAT, Drum HAT, and Piano HAT to create a mini music box, following Pimoroni’s online guide. This worked well, even though the pHAT Stack configurator flagged up a possible pin conflict on BCM 21.

Other suggested setups include an alarm clock (Four Letter pHAT, Touch pHAT, and Speaker pHAT) and a weather station with built-in dashboard (Enviro pHAT, Four Letter pHAT, and Scroll pHAT). You could even solder a female header to a Pi Zero and mount that on the Stack’s bottom header, rather than using the ribbon cable.

pHAT Stack review: The last word

Whether you use it for a specific project or just for experimenting with combining various pHATs and HATs, the pHAT Stack is a well-designed breakout board that should prove useful. You just need to watch out for those GPIO conflicts – and check that the cable is connected the right way round on the Raspberry Pi.