I just bought a wifi module shield and using it with Arduino. I power Arduino (with the wifi shield on it) via USB from the PC. I need to demonstrate it without using the PC as a power supply. And I cannot also use 2.1 power plug or 9V adapter jack since i don't have that component. I don't have time even to buy that.

So the only option for me is to use the Vin pin with a 9V battery. I am just afraid if i may damage the wifi shield or Arduino. I read some warnrnings about that.

Is the Vin pin used only with Arduino without a shield on it?

Thanks in advance,


When you are realy in such a hurry, you could attach the wires of the battery with some tape to the spots I marked in the picture. Maybe the bottom is easier to get the wires stick to.


When I remember right (1) is +9V and (2) is GND. The integrated diode should prevent damage, if you connect it the wrong way.

After taking a look at the schematic I would mean, that connecting the battery to VIN is save. Just be carefully not to change polarity, because you skip the protection diode. This forum thread approves my thought.

In the comments you asked, whether you could use an additional external diode to increase safety. In my opionion this is not neccessary. It is just getting more complex. Get two colored wires (black, red) and connect them to the battery, so you can immediately see whats GND. When you connect the wires, just pay attention.

  • \$\begingroup\$ I think it is the other way around. A multimeter can measure the resistance between 2 and GND (should be near 0 if I am right). \$\endgroup\$ – jippie May 5 '12 at 15:54
  • \$\begingroup\$ @jippie - You are right. The center pin of the jack is positive and connected to (1), so (2) is GND. \$\endgroup\$ – PetPaulsen May 5 '12 at 16:01
  • \$\begingroup\$ @PetPaulsen I think as you say connecting 9V battery from the jack is safer. Vin way is a bit risky since if one connects the opposite way things might burn. So my only concern now how to connect the wires to the 9V jack in a stable way without soldering. hmmmm.. \$\endgroup\$ – user16307 May 5 '12 at 16:11
  • \$\begingroup\$ @cmd1024 - Yes, connecting the wires could be tricky. Maybe you got some aluminium foil tape? Probably not ... \$\endgroup\$ – PetPaulsen May 5 '12 at 16:21
  • \$\begingroup\$ I just connected 12V from an adapter no doubt backwards and it is still standing. What's this burning nonsense?:) As the cable from the 9V (if you have the cover) is braided, you could probably get away with taping it with any tape down on the board. Taped down, then taped around the board multiple times for strength. May leave residue afterwards, but it should give enough contact (over the oxides formed) to work. \$\endgroup\$ – Tom Paris May 5 '12 at 21:16

Vin is not the correct pin, it is related to the reference Voltage of the ADC's only.I stand corrected. I confused AREF with Vin.

I've used the +5V and GND pins before which worked for me with a 5VDC power supply, but I don't think the normal voltage regulator likes being reverse powered and will eventually die from it. One of my Arduino's has a little jumper link on it especialy for this purpose, being powered from USB, directly powered or through a higher voltage on the jack.

I just read you are using 9V battery; in that case you can use the jack plug only!! What do you mean by not having it? Is the voltage regulator missing too?

  • \$\begingroup\$ i dont have the jack(plug) which enters to the Arduino jack. Or should i say i don't have these components: arduino.cc/playground/uploads/Learning/9V_tut_1.jpg Are you sure that i cannot wire up the 9V battery to Vin and ground and use that way? \$\endgroup\$ – user16307 May 5 '12 at 15:46
  • \$\begingroup\$ Don't do it. I am sure you are able to wire it up, but I am also absolutely sure that you will regret it. You'll blow at least the microcontroller and probably other components. \$\endgroup\$ – jippie May 5 '12 at 15:52
  • \$\begingroup\$ look at this example: instructables.com/id/Arduino-Wireless-SD-Shield-Tutorial/step7/… I saw some other examples. \$\endgroup\$ – user16307 May 5 '12 at 15:57
  • \$\begingroup\$ I think I am confused with the AREF pin and you may be right indeed. In that case the pin should measure near 0 ohms to the middle pin on the jack plug. \$\endgroup\$ – jippie May 5 '12 at 16:03
  • \$\begingroup\$ The schematic shows, that you will skip the protection diode, when you connect to VIN. So be careful not to connect the wires the wrong way, because this could actually fry your Arduino. \$\endgroup\$ – PetPaulsen May 5 '12 at 16:05

The Arduino VIN pin is connected after the Barrel Jack and Reverse Protection Diode, and before the 5v regulator. It is designed to have power input there. What you normally should not do is provide power directly to the 5v pin, unless you are sure of what you are doing.

The Wifi shield uses the VIN pin as well, to power it's 3.3v switching regulator. You may find it hard to insert a wire into the VIN pin socket, AND have the shield plugged in at the same time, but due to the design of the Arduino shields using pass through extended lead headers, you can plug in the 9v battery to the Wifi shield's VIN pin header and it will work for both.


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