A shield is an add-on board that plugs straight onto the headers of a microcontroller board (typically an Arduino) to add a function to it — motor driving, display, sensors, communication — with no wiring at all. Not to be confused with a module (breakout), which does the same kind of job but is wired up with jumper leads → Wiring a module for Arduino, Wiring a module for MicroPython.
The stacking principle
A shield reproduces exactly the header layout of the host board: it sits on top, pin on pin, and several shields can sometimes be stacked. The point is speed of prototyping: no flying leads, a mechanically solid assembly, a function added in seconds. This is one of the reasons for the success of the Arduino form factor, whose header layout has become a de facto standard picked up by a great many boards. On the software side, every shield comes with its own library, which exposes the function without your having to know the internal wiring. Putting it to work: Using a shield for Arduino, Using a shield for MicroPython.
Limits
A shield takes up a fixed set of pins: stacking two shields that both claim the same pin creates a conflict no wiring can resolve. Beyond the prototype, a shield stays bulkier and less reliable than a dedicated printed circuit board integrating the same function. That is the natural next step once the architecture settles.
See also
- Microcontroller — the host board
- Arduino — the reference form factor for shields
- Library — the software counterpart of the shield
- Arduino — shield — putting it to work in practice
- MicroPython — shield — the same board driven from MicroPython
- PCB — the integrated alternative once past prototyping