multiple shields

Projects General Guidance
1

This seems too dumb to ask, but I haven't found the answer to my question here or on Google. It's about stacking shields.

I'm working on a project that will require a stepper motor shield, the excellent host USB shield and an LCD shield. For sure, some of these use the same IO pins.

I could unsolder the pins that conflict and hard-wire them to unused arduino pins. It's just that I've never found an explicit description of the process.

I think I would proceed by figuring out which pins are used by multiple boards. Unsolder those header pins, and put wire in their place. Reroute so that pins on the shield now go to different pins on the duino 2560 mega. Then I go into the software and change the pin numbers that I moved.

I assume all the shields can use the same power source, except for separate motor power.

What am I missing? Is there a better way? Do I also need to go into the libraries looking for pin assignments? Is there a description somewhere of how this is done?

Thanks, guys!

Tom

2

Is there a better way?

Not really, this is a limitation of the Arduino design IMO.

There is a "shield" that allows you to map the pins, IIRC you place it between other shields and solder/insert jumpers to remap the signals.

I think there was a thread about it here.

Rob

3

So there's nothing wrong with my idea of unsoldering the conflicting pins, hardwiring so that each shield is connected to unique pins on the Arduino, and then change pin assignments in the software?

That seems like the obvious answer, but I've never seen an explicit description anywhere. All I see are posts saying they can be stacked, not talking much about pin conflicts.

I could just try it, except I can't think of a way to do it without cutting/destroying the headers, and I don't want to mangle my boards on a hunch.

Thanks for the response, Rob.

4

Waitaminnit. I'm not thinking. I could try this without mangling my headers.

I'm going to insert jumpers into the existing headers, duh. Where I need to share pins, like power and ground, I'll use a breadboard to give me multiple places to plug in.

Good grief, so obvious.

5

Graynomad:
There is a "shield" that allows you to map the pins, IIRC you place it between other shields and solder/insert jumpers to remap the signals.

Sorry for replying to an old post, but I found it with the same need (remapping pins). I found this - kinda large, but works.
http://smartmaker.com/en/shields/54-mix-up-universal-router-for-arduino.html

-- Steven

6

This seems like something you would only use as a desperate last resort. The shield system is quite good and I think pin clashes are usually fixed on the shield causing it.

7

Mayhew labs make a very nice 'go-between' shield that solves this problem quite nicely, if you don't mind the extra vertical height. If you don't like fancy spending money on it, you always have the option of connecting the shields by patch wires and not actually stacking them at all.