So far, we have always had our Arduino connected to the computer via a USB cable. It’s convenient, it’s easy, and it allows us to program and provide power at the same time.
But one of the great things about Arduino is that it can run the program autonomously. We don’t want to follow it around with the PC, or have a 50-meter USB cable.
We need our Arduino to be autonomous. That is, to work without a PC. And for that, we need to power it (i.e., give it current).
Today we are going to look at the main ways to power our board and, most importantly, what voltages are safe to avoid frying our Arduino.
The USB Port
This is the one you already know. When you connect the cable to the computer, Arduino receives 5 Volts (5V) regulated and ready to use.
- Voltage: Exactly 5V.
- Source: Computer, phone charger, or Powerbank (external phone battery).
- Ideal use: While programming, testing on the desk, or for projects that consume little power.
The Barrel or DC Jack Connector
If you look at your Arduino UNO board, you’ll see a black round connector in one corner. That’s the DC Jack. It’s designed to connect batteries, power packs, or wall adapters.
Here a key component of the board comes into play: the Voltage Regulator. Arduino works internally at 5V. If we feed it 9V through the Jack, the regulator takes care of “cutting” the excess and converting it into stable 5V.
- Recommended Voltage Range: From 7V to 12V.
- Source: The typical square 9V battery, a battery holder with 6 AA batteries.
Why a minimum of 7V?
Because the regulator needs a small margin (about 2V extra) to work. If you feed it 5V or 6V here, the Arduino will receive less than 5V and will malfunction.
Why a maximum of 12V?
The regulator converts the excess voltage into Heat 🔥. If you feed it 20V, the regulator will get hot and could burn out to protect the board.
The VIN Pin
If you look at the POWER pins, you’ll see one called VIN (Voltage Input). This pin is internally connected to the DC Jack.
- Use: If your battery doesn’t have a Barrel Jack, but two loose wires (Red and Black), you can connect them here.
- Connection: The Positive (+) wire goes to VIN. The Negative (-) wire goes to GND.
- Voltage: The same as the Jack: 7V to 12V.
The VIN pin has no polarity protection. If you connect positive and GND backwards by mistake, 💥 you will burn the board instantly. Check the cables twice.
The 5V Pin
At some point you might wonder: “If Arduino works at 5V… can I connect 5V directly to the pin labeled 5V?”.
Technically yes, but I don’t recommend it if you are just starting out.
The 5V pin is intended to be an OUTPUT (to power sensors), not an input. If you feed power there, you bypass the voltage regulator and the safety protections.
- If your source provides 5.5V → 💥You could burn the chip
- If there is a voltage spike → 💥Goodbye Arduino
- If you connect USB at the same time → 💥 Electrical conflict (goodbye to your PC’s USB port?)
For safety, use the 5V pin only to power sensors, not to power the board.
