Power supply pin as power input


Is it possible to use the 5v output pin on the arduino as “input power supply” for the arduino?
Or would that release the black smoke from a chip somewere…

I assume you mean: Use the 5V output on one aduino to connect to the input power supply of another arduino. If so then no, you probably won't fry anything - it just won't work. The input power supply is connected to the input of the 5V voltage regulator. The voltage regulator input needs a couple of volts more than 5V to work.

If instead you were planning on connecting the 5V out to the input power supply of the same arduino, then yes this will probably result in the pesky black smoke escaping.

From the schematics of both the NG and Deicimila it looks like there wouldn't be any problem powering the first arduino with external power (not USB!), and then connecting a jumper from the 9V pin to the 9V pin on the second arduino. This assumes that your external power supply can source enough current for 2 arduinos.

Actually you can connect +5V and GND from one Arduino board to another Arduino board(to the same exact +5V and GND pins) to power the second Arduino. Watch for the total current... the voltage regulator included in the board is good for 500mA to 800mA. USB is good for up to 1A and the new Diecimila has a current overload protection PTC switch.


USB is good for up to 1A …

No sorry, not true. An USB-port (see USB-Specs) provides a maximum current of 500mA, thats it. A good USB-Hub will switch your port off, when you go beyond that limit. Cheap ones might deliver more current up to the point where other USB-devices plugged into the hub quit working.

If you need more than 500mA get an external power-supply.


USB is good for up to 1A

on USB spec. at the first enumerate process, Device descriptor, USB current should not take over than 100mA after that USB will adjust load demand by Config descriptor upto 500mA as I remember FTDI default config value is 100mA (if more , must re-config EEPROM) also explain on FTDI datasheet, the more power was controlled by FET and enable after connection success (/PWREN)

then use external power supply as Eberhard (wayoda) said is right and earier things..

Thanks for the detailed information about USB power supplying capacity!

Just adding my 2c: I believe USB 2 defaults to 250mA.


Just adding my 2c: I believe USB 2 defaults to 250mA.

No, didn't change with 2.0. Its still at 500mA. But as worapoht already mentioned, its the duty of the device plugged into the USB-port to request the maxium power it wants to consume. My ArduinoNG requests 90mA from the Hub to which it is connected. (On linux open a console and run command : sudo lsusb -vvv -d 0x0403:0x6001 to print the complete USB-config of the USB2Serial FTDI chip) The hub will gratiously make that 100mA because that is the minimum unit every USB-hub must be able to supply. From then on it all depends very much on the hardware you buy. I have Hub that would rather let itself evapourate in a cloud of smoke than to switch off a port that demands too much current. I love that one, but don't run it unattended, it might burn down your house! Eberhard

No, didn't change with 2.0. Its still at 500mA.

I said default. So its 250mA instead of 100mA for USB 2 devices.

I took the original question another way. I thought ugilten was asking if you could power the arduino by putting a 5V source onto the female hader marked "5V", which typically is seen as a 5V source.

If so, then yes, you can do that. Just make sure the power source you are using is fairly well regulated.