When we needed to add new hardware to the Pioreactor, we've chosen the very simple and very funny solution: stacking HATs. That's right, we're stacking HATs right on top of each other.
The stacked HAT mechanic provides a user-friendly and modular way to extend a Pioreactor's hardware. We can design and build new HAT hardware to extend functionalities. Users can mix-and-match which HATs they want to use, and the community can design HATs, too. Stay tuned for a tutorial video on how to do this!
Our first HAT is the Temperature Expansion HAT¹ that provides a connector to a new in-situ Pt1000 temperature probe. We're very excited about this HAT, as it opens up the door for lots of new Pioreactor operations: ability to grow thermophiles, faster heating and cooling, stable temperatures during dosing, and more.
Future HATs will have more PWM outputs, more LED outputs, display screens, etc. There's lots of potential!
Not everything needs to be a HAT though. We have some future accessories that won't use the stacked HAT mechanic. We are reserving HATs for hardware that needs more power (think: 5V), more structural needs, or works over a communication protocol that isn't i2c (since i2c devices can use the STEMMAQT connection).
¹ technically these new HATs aren't true HATs according to the Raspberry Pi Foundation, as they don't have an onboard chip called an EEPROM. Our original Pioreactor HAT has an EEPROM, though.