Schematex
breadboard·Fritzing visual conventions (no ISO standard)·education, maker, hardware·complexity 1/3

Blink LED on Arduino Uno

The maker hello-world. Arduino Uno + 220Ω resistor + 5mm red LED — D13 → resistor → LED → GND. Tests basic part placement, beside-left MCU, and the iconic Bézier wire arc.

For the Arduino beginner

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Blink LED — Arduino Uno hello-world Breadboard wiring diagram generated by Schematex Blink LED — Arduino Uno hello-world 5 10 15 20 25 30 5 10 15 20 25 30 a a f f b b g g c c h h d d i i e e j j D13D12D11D10D9D8D7D6D5D4D3D2TXRXRST3V35VGNDVINA0A1A2A3A4A5Arduino Uno R1 220Ω D1 (red)
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The "Blink" sketch is the Arduino equivalent of printf("hello\n") — the smallest program that proves the toolchain, board, and wiring all work. The breadboard wiring routes D13 through a 220Ω current-limiting resistor into the LED's anode (long lead, row e), and pulls the cathode (short lead, row f) down to ground via the bottom rail. Power and ground rails are jumpered from the Uno's 5V and GND pins on the left.

If the LED doesn't light up, three things to check, in order: LED polarity (the flat-side flag in the diagram is the cathode); resistor value (220–330Ω works for a 5mm red LED at 5V); and that D13 is the actual pin you're toggling in your sketch.

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