Relay integration

[MarkHaysHarris777]

is this the "3v Arduino Nano"   http://goo.gl/oHtVZx   ?

Yes, another fine option too. 

... not as robust as the Gertboard mind you, but a 3v3 system compatible with the PineA64, and again, a micro controller for handling the low-level stuff, while the PineA64 handles the high-level stuff.

I guess I really don't know what you're doing with your garage door project exactly... and probably, not definitely, the Arduino nano may be able to handle it alone... only you will be able to judge that.

( check carefully whether the arduino products you purchase use a 5v or 3v3 system )