An Arduino can be connected to an external power source in a few standard ways. Which one you use depends on the board model and what voltage you have.
Common external power sources (most Arduino boards)
1. USB (5V)
- Power from a PC, USB charger, or power bank via the USB connector.
- Example for Uno: it can be supplied from the USB connector (5V).
2. DC barrel jack (typically 7–12V recommended)
- Many boards (Uno/Mega/Leonardo) accept an external DC adapter via the barrel jack.
- Uno: DC power jack (7–12V) recommended.
- Mega 2560: input recommended 7–12V.
- Leonardo: input recommended 7–12V.
3. VIN pin (typically the same as barrel-jack input)
- You can feed the board through VIN with a higher voltage that the onboard regulator converts to 5V (or read VIN when using the barrel jack).
- Uno: can be supplied via VIN (7–12V).
- Leonardo: VIN is the input when using an external source (vs USB 5V).
4. Regulated 5V into the 5V pin (only if you know what you’re doing)
- This bypasses the onboard regulator and can damage the board if the 5V is wrong or backfeeds USB.
- Uno explicitly warns that supplying voltage via the 5V pin bypasses the regulator and is not advised.
Board-specific summary
Arduino Uno Rev3
External power options: USB 5V, barrel jack 7–12V, or VIN 7–12V.
Recommended input voltage: 7–12V (also has an input limit range listed in specs).
Recommended input voltage: 7–12V (VIN / barrel), or 5V via USB.
Arduino Nano (classic)
- Can be powered via:
- Mini-B USB
- 6–20V unregulated external power supply (pin 30)
- 5V regulated external power supply (pin 27)
- It also notes the power source is automatically selected to the highest voltage source.
Practical “how to choose” (fast rules)
- If you have a USB power bank/charger → use USB 5V.
- If you have a 9V/12V adapter → use the barrel jack (Uno/Mega/Leonardo) or VIN.
- If you have a clean regulated 5V rail (DC-DC buck, lab supply) → you can feed 5V pin, but be careful (avoid backfeeding; ensure it’s truly regulated).
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