Arduino [/ˈarduino/] n - Arduino is an ecosystem of microcontroller boards built about simple 8-bit or 32-bit processors. Unlike a Raspberry Pi, it runs no Linux; it runs a single program that reads inputs, turns a tight loop, and sets outputs. That makes it fit for small, deterministic, low-power tasks.

Wherein Its Usefulness Lies

• Real-time response. [/ˈrɪːltɪmɛ ˈrɛspɒnsɛ/] n A microcontroller can answer a sensor’s change within microseconds, with no operating system standing between.
• Low power. [/ˈlɒw ˈpɒwɛr/] n An Arduino may sleep through most of the day and wake on a timer or an interrupt; a small battery will keep it running for months.
• Simple hardware. [/ˈsɪmplɛ ˈhærdwærɛ/] n The board lays its analog and digital pins bare. One need not master a kernel driver model to read a sensor.
• Cheap enough to abandon. [/ˈkhɪːp ˈɛnæʊgh ˈtɒ ˈæbændɒn/] n At a few dollars the board, it is feasible to set one sensor node to each rack or machine.

Its Limits

• No networking by default. [/ˈnɒ ˈnɛtwɒrkɪng ˈbi ˈdɛfæʌlt/] n A basic Arduino has neither Ethernet nor Wi-Fi. You add a shield, or choose a board with connectivity built in, or speak to a gateway over serial.
• No storage or complex logic. [/ˈnɒ ˈstɒrægɛ ˈɒr ˈkɒmplɛx ˈlɒgɪk/] n If you must log history, serve a web page, or run a Python script, a Raspberry Pi or a Single-board computer is the better instrument.
• 5 V or 3.3 V logic. [/ˈ5 ˈv ˈɒr ˈ33 ˈv ˈlɒgɪk/] n To interface with industrial sensors carrying 12 V or 24 V signals wants level shifting or protection circuits.

Of Its Place in These Pages

Arduino appears in On the Making of Bespoke Devices as the low-power, real-time choice, and in Bespoke Devices for the Datacenter as part of the toolkit. See also Raspberry Pi and Single-board computer for the trade-offs on the compute side.