Wifi Rev 2 Code not working on DC Power

I ordered 2 Wifi Rev 2s and when I upload my code onto them the code works perfectly when they are powered by the computer. The problem comes when the Arduino is powered by a DC power source. The Arduino turns on but the code cycles and constantly turns an LED on and off. The code is designed to only turn the LED on when an input is received from a pressure sensor. Hopefully someone can help me.


I have tried several, I currently am powering it by a 9v battery. I have tried a 9v 1 amp power supply, a 5v 1 amp, and a 12v 1 amp. The board does the exact same thing for all of them. It turns on and constantly turns the LED on and off.

I think that
A full wiring diagram is the minimum that is needed (photo of hand-drawn one is fine).
We need to know which pressure sensor?
We need to know which LED; the one that is controlled by your code or the power led?

The square 9V batteries are useless.

  1. Attached image is the wiring diagram
  2. The pressure sensor is a MPX5500DP
  3. It is a diode LED plugged into pin 11.

(mod edit)


Yes I have Serial.print output in my code

Do you have a resistor in series with the LED. If not, you’re overloading the onboard voltage regulator that brings your 9V/12V down to 5V.

What do your serial prints tell you?

I have tried adding a resistor in series with the LED, all it does is lower the brightness of the LED which was expected by adding a resistor in series. My serial prints are showing a count that goes up when the pressure sensor is activated.