Background, I am building a prototype that has an internal circuit board controlling RGB LEDs. Due to size restrictions on the actual prototype I have to use the Pro Mini 5V board to install in the casing. Also, I need to power the board with a series of to 3V batteries (for a total of 6V) instead of the 5V supply from the USB.
I did all of the intial circuit building and programming with an UNO board. I tested the UNO circuit with both the USB 5V supply and the exact 6V battery supply that I am using. Everything works perfectly. I soldered up the circuit and components completely on the Pro Mini 5V board. I tested it with the USB 5V supply attached to the computer and it works perfectly. However, when I attach the 6V battery supply it will not work. Each time I press the button in the circuit the board seems to reset.
Any thoughts or help?
My initial assumption is that the Pro Mini 5V can not handle the 6V supply and resets to protect itself. Any help is greatly appreciated.
I am still leaning towards the voltage as it is the only changing variable. Like I mentioned, it works perfectly with the 5v usb attached to the VCC.
USB is an active supply while batteries are a passive supply. By that I mean compare the two. The USB supply is better regulated and may be providing some current limiting. Batteries will show just show a decreased voltage in the presence of a high current draw.
It could be there is a wiring mistake with the Pro Mini setup that is better protected when used with USB than when used with the battery. This is why I suggested making voltage measurements to get an idea of what is going on.
Have you taken the batteries back to your Uno to make sure they have enough energy left to work correctly?
I tested all of the things that you had recommended (testing the draw, re-checking with the uno) and again everything seemed fine. However, your comment about the pull up vs down resistor got me thinking. So I switched the resistor and presto, it works perfectly again. Not sure why the difference between the UNO and Mini Pro, but hey, it's working now.