Sorry if this is seen as a repost, but after wandering around it seemed that this section was more appropriate.
We have been getting problems recently with arduino boards.
We use I-wire on pin7 for some ibutton reading and had the arduino R2 halting immediately on powerup. Pressing the reset button once after it hanged makes it boot correctly. We finally found that simply taking a 4.7k resistor from the board 5V to pin 7 causes the problem. On original UNO, this works.
Can you reproduce? (we can, each time, using any program, even 'blink') I have been trying on about 8 of the 40 i have in the office and all hang on startup with the resistor. I'm wondering if it's a design problem or just the serie.
Has anyone got any idea on what causes this behavior and how to solve it?
Thanks a lot.