[Resolved] Arduino Help Needed

I am working on an Arduino project and am confused by how to power the Arduino without USB. Here is the Arduino that I have:


I believe this is the schematic of the board:


I have been able to program “blink” with the USB cable. Blink works.

But, if I disconnect the USB cable and try to power the device from +5VDC, the light on the board stays on; no blinking.

My external +5VDC is provided by a linear regular from a 12V vehicular battery. So, the external power is accurate and stable without ripple, etc.

Looking at the schematic, it appears that 5V from the USB goes to exactly the same place as the 5V pin.

Any ideas what I could be missing? Here is a video we took this morning to illustrate the behavior:


Note that, in the video, the USB cord continues to be plugged in. But, the external power is not applied. I.e., the regulator is not providing any power. The 5V regulator and GND are the only pins that are hooked up to anything when the Arduino is plugged into the socket.


Could we get a top down look at your breadboard with and without the Arduino plugged in? Grounding pin 11 will cause the LED to stay on and it’s right next to the actual ground pin, so, easy to get shifted.

Also, if you have the Arduino send back something via the USB serial terminal while you plug it in you’ll be able to tell if the processor is stopping or if it’s a different issue.

We’re checking Pin 11. We verified no continuity between pins and then put high temp silicon RTV red around them. But, it appears that Pin 10 and 11 may be connected now. Removing the RTV…

Ok. That was the problem. We’re not sure how the connection happened. We removed the RTV and observed no continuity again. Blink worked. So, I just put new RTV on.