How to Connect an LED to 5V: Wiring, Resistor and Mistakes to Avoid

Quick answer: wire the 5 V supply through a series resistor to the LED anode, and the cathode to ground. For most indicator LEDs on 5 V, a 150-330 Ω resistor sets a safe 10-15 mA.

Step by Step

• 1. Identify polarity: long lead / no flat edge = anode (+).
• 2. Pick the resistor: R = (5 - V_f) / I. Red (2 V, 10 mA) → 300 Ω, use 330 Ω. White/blue (3.2 V, 10 mA) → 180 Ω.
• 3. Connect: 5 V → resistor → anode; cathode → GND. Resistor position (before or after the LED) does not matter.
• 4. Power up and check brightness and resistor temperature.

Three Mistakes to Avoid

• No resistor: a bare LED on 5 V exceeds its rated current in seconds.
• Reversed polarity: reverse voltage over ~5 V damages the die; the LED may survive briefly but degrades.
• Ignoring tolerance: a "5 V" USB rail can be 5.25 V — leave margin in your current budget.

Multiple LEDs on 5 V

Two red LEDs in series (4 V total) can share one small resistor; blue or white LEDs (3.2 V) must run one per resistor in parallel strings — 2 × 3.2 V exceeds 5 V minus driver headroom.

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