It’s not often you see AC power input as a feature on a microcontroller board this tiny! This ATtiny85-based board is designed with the model train community in mind, hence the AC input requirement. The designer, Mark’s Gadgets, has managed to squeeze not only the ATtiny85 but also a full bridge rectifier and 5V linear regulator onto a board that is 13.5mm²! Of course, it can also accept DC up to 32V. Because of the wide input voltage range, it can also utilize batteries from 2S (7.4V) all the way up to 7S (25.9V), which makes it usable in other RC projects like drones, RC cars & boats, or any battery-powered project which needs a microcontroller.
The form factor is very interesting. It utilizes a larger outer frame with pads for programming and testing, but this frame can be snapped off once ready for use, significantly reducing the size of the board. 5 of the output pins have 480Ω resistors in-line, meaning they can be directly attached to LEDs, simplifying the usage for model train props that have lighting. A great example is this ambulance prop, used in a model train set, being powered by this board!
Of course, there’s no reason why this has to be limited to model train usage. It’s a perfectly capable ATtiny85 development board that would be ideal for wearables, especially electronic jewelry or decorations. It seems the popularity of the ATtiny85 continues to grow!