# Are the 3.3V and 5V pins on an Arduino input or output?

I need a 5V supply for a device I want to control with my Arduino, and was wondering if the power pins on the side of the board are solely for powering the board, or if i can take a line from them and power other devices?

I know there are other answers to this question but they seem quite complicated, and I am very new to Arduino.

Also what's with the VIN pin? I saw somewhere it is 9V?

• You need to research how much current can be taken from these pins without causing the Arduino problems. There should be a spec somewhere. Commented Apr 22, 2020 at 10:52
• Post the schematic of the board. Commented Apr 22, 2020 at 11:10
• There are more than one arduino boards, at least, be specific about it. Commented Apr 22, 2020 at 11:13
• The pins are outputs, but how much current you can draw depends on the board. Look at the documentation, or look at the schematic to derermine which power converters are used, and how much current they can deliver. Commented Apr 22, 2020 at 11:53
• I recomend you to visit this site: link. Commented Apr 22, 2020 at 12:03

To add to Jay's answer, here are some more specifics on the actual way the V_in, 5V, and 3.3V voltages are generated. Again, since you did not specifically say which board you are using, I will operate under the assumption that you are using the good old Arduino Uno. You can refer to the following as I go:

V_in is the voltage that you input to the board through either the Power Port or the USB connector. You made reference to this being 9V, and this is usually the case if you are plugging a 9V battery into the barrel connector like so:

This V_in voltage goes into the Voltage Regulator in the diagram, and you can look up the datasheet of that part if you would like to learn more about the voltage limits, etc. A similar part is LM7805 if you want to look at how that works:

The output of that voltage regulator is what produces the 5V which is available at the 5V pin. The amount of current you can pull out of this again corresponds to the values outlined in the datasheet of the voltage regulator.

Finally, the 3.3V is actually produced by the part labeled USB Interface Chip. Here is the datasheet for the part:

https://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdf

I'll save you some digging, the max current you can pull from this pin is available in the first box on page 8 (50 mA).

So to answer your question, as long as you do not exceed these current limits, or get too close to them (thereby disrupting to Arduino's power source), you should be able to use them as you please.

To start off, there are many variants of the Arduino board. Depending on what components are on the board will determine how much current you can draw from the 3.3V and 5V pins. So you're better off checking the schematic of the Arduino you had in mind.

But to answer your question, the 3.3V and 5V pins can be used to power external devices. But I can't say how much current you can pull since that depends on the board design. You can probably power an LED or something, but not charge a phone. The VIN pin is where you supply power to the Arduino. You use this pin if you are powering the Arduino from a voltage source higher than 5V (or 3.3V if that's what the Arduino takes) since the voltage is stepped down to 5V and regulated.