I have built a prototype Arduino shield/Arduino derivative board thing, but before I produce a final release version I have been wondering the following.
When providing 0.1" headers for I/O on the board, what pin layout order should I use for GND, 5V and signal? I cannot seem to find a standard described anywhere. If I look through my collection of Arduino boards and accessories, I find most are GND, 5V, then signal, but not always. Some are GND, signal, then 5V. If there is a proper standard I'd like to follow it for the board I'm designing. I'd like to think that if there is a standard (say) temperature sensor out there with 3-pin plug, that my board would accept it (rather than blow it up!).
I'm planning on using the commonly available keyed Molex KK headers 0.1" pitch. Same as the Tinkerkit http://store.arduino.cc/ww/index.php?main_page=product_info&cPath=16&products_id=253
. Incidentally Tinkerkit have Signal on the middle pin.
A secondary question that arises - which signal should be on pin 1? Some of my Arduinos are pin 1 = GND, others pin 1 = 5V. This of course only matters with keyed headers as an un-keyed varieties can be plugged in either way round (the right way and the likely terminally-kill-the-part way).
Perhaps since there doesn't appear to be a clear dominating standard I should instead assume no standard and just do it the way I choose?