Arduino relay shield (homemade)

Hi! This is my homemade arduino relay shield, I had a spare 12V relay, and nothing to do with it, so this project happened.
The circuit is roughly the version seen in the schematic on the left, with a BC548 (NPN) transistor and a 1N4007 diode, my resistor was of 8220 Ohm.
The ground (GND) has to be the same on the arduino and on the relay shield, or it will not work.
On the picture you can see on the bottom part the + (Vcc), S (signal from arduino, any digital port), and - (GND), on top we see the connectors for NO, (normally opened) C, (common), NC (normally closed).
For the whole article, you can follow the original instructable that I based on, here.