Problem using external power jack onArduino Uno R3 [Solved]

Any program I make powering the Arduino with the USB connector works ok.
If I use the Power Jack, the Arduino on light is ok, but the programs do not work.
Can anyone please help?
Thank you PaulRB & MichaelMeissner for your help.
I was using a 5.3v phone type power supply.
It now works ok with a 9v battery.
In future I will use MichaelMeissner suggestion and fit a rechargeable 6 x AA Nimh battery pack.

Do you have a multimeter? Measure the voltages on Vin, 5V and 3.3V connectors, both with usb power and external power and post the results. Don't forget to connect the black multimeter connector to the GND output.

Also tell us about the external power supply/adaptor you are using. What's the voltage and current capabilities?


I would imagine whatever you are using to power the Arduino is not supplying enough current. It is recommended that you use 7-12 volts. I didn't see a maximum amp draw, but you probably should have at least 200 mA. The 9 volt batteries used in smoke detectors really don't have that much power, and you should think about alternate power sources, such as 6 rechargeable AA Nimh batteries (7.2 volts).