Board performs OK with USB Cable but not with Wall Adapter

Hello All,

I am having a confusing error wherein a very basic sketch of Blink an LED performs perfectly when I feed the board with the USB Supply from my laptop. But when I feed the board with 12V 1A Power Adapter, the LED does not blink, it remains ON constantly (and flickers randomly in between). Also, with the power adapter plugged in, the reset button doesn't seem to work.

What could be the possible cause? How to rectify it?

Hi rptduino

What type of Arduino are you using? And how do you have the external power supply connected to the Arduino?

Regards

Ray

See also the OP's other Thread.

There have been 3 or 4 Threads recently about different behaviour using USB power and "non-USB" power. I don't recall that any of them resolved the issue.

If this really is a problem it would be nice to get to the bottom of it.

@rptduino, can you post the code that is causing a problem so I can try it. (and answer @Hackscribble's question).

...R

Hi Ray,

It is Arduino UNO. I connected the adapter through the power jack on board.

@robin: I don't think problem is code specific as I got this problem for the code for Basics-> Blink in Examples in the Arduino IDE. It blinks normally when USB power is fed in, but it remains constant when power is fed through 12V 1A power adapter. Previously, this board performed well with 12V 2000mAh (fed through Vin pin) battery.

Do you have a multimeter? With the 12V external power supply, it would be interesting to measure the voltage on the Arduino Vin and 5V pins (with respect to GND pin).

rptduino: @robin: I don't think problem is code specific as I got this problem for the code for Basics-> Blink in Examples in the Arduino IDE.

OK I will try this myself later.

...R

I have now tried an Uno working from ( A ) the USB connection, ( B ) 6 AA alkaline batteries in a battery holder and ( C ) a 12v 3A wall wart. I tried the basic Blink program and the program in this Thread which also includes a potentiometer and servo.

They all worked as expected.

Are you sure that your wall wart is making a good connection when plugged into the Arduino? Mine needed a lttle fiddling to get it to work. There are different standards for those concentric power connectors.

...R

It seems on board 7805 has something to do with it.

Here’s what is happening: <Controller programmed to blink LED at pin 13>

  1. Power up through 12V 1A wall adapter jack:
    ON LED Glows. LED on Pin 13 remains constant.
  2. Power up through 12V 2000mAh battery, connected on Vin Pin and GND Pin:
    ON LED Glows. LED on Pin 13 remains constant.
  3. Power up through USB Cable:
    ON LED Glows. LED on Pin 13 blinks as expected.
  4. Regulated 5V fed through an external 7805 regulator connected on 5V Pin and GND Pin:
    ON LED Glows. LED on Pin 13 blinks as expected.
  5. Power up with both USB and Wall adapter plugged in:
    ON LED Glows. LED on Pin 13 blinks as expected.

Can you please explain what should I deduce from these 5 different cases?

P.S.: When the board was new it performed as per the expectations in all the 5 cases, but recently, it is doing so only in the cases 3, 4, 5.

On some boards in some situations the unconnected RX line into the serial port can pick up enough rubbish to stop the boot loader timing out. The solution is to put a 1K pull up resistor from the RX input to +5V.

@rptduino, if @Grumpy_Mike's suggestion does not solve the problem draw a diagram of how everything is connected and post a photo of the drawing.

...R