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!).
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?
Yeah, in the absence of any other ideas I think I'll follow what has been done with Tinkerkit to make things mix and match. I think I'll make my four pin 1-WIRE connector the same pin out as Tinkerkit too.
What I am thinking is a 5-wire connector with symmetric pins say 5V-out-gnd-out-5V so even if you plug in wrong it will still work Just a thought, like apple's new connector.
Well I've decided to go with the defacto standard that a lot of sensors use. That is, the ordering GND, VCC, SIGNAL. The advantage of this is that if people use a bare header on my board they can plug in directly a defacto standard sensor. If people decide to use a keyed KK header instead (the silk screen will have the drawing of a keyed KK header) then they will have all the advantages of a connector that doesn't easily get knocked out. In this case, the pin out will be 1-GND, 2-VCC, 3-SIGNAL. This is not compatible with the Tinkerkit, but as I dig deeper it looks like the Tinkerkit gear, at least at this point in time, really isn't that popular and so not much to be gained from a pin out that would not be as flexible as the one I've decided upon.