Made the changes to the sketch as suggested, and now I can connect it to NO.
Just to make sure I didn't made a mistake while soldering, used a fresh nano and made all connections again. In the sketch the changes still need to be made, however as far as i could test this morning all is working fine now!
Thanks for all the tips!
The relay is powered by the same powersource as the arduino (6 port powered usb hub 2A).
Sure, no prob.
This is the relay, at the moment a 6 port, didn't had a one port available.
The green wire is connected to IN1 on the relay and pin4 on the arduino.
the backside of the print. The bottom row 'S' is pin 9 on the arduino, 'M' and 'K' is pin3 and Ground to doorbellbutton.
front side. The brown and blue on the left are 5V to the relay, on the right red and blue are input doorbellbutton.
Yeah i know. Does it matter? It's seperated by the relay from the rest right?
Or am I saying something stupid here.... 
Just to make sure I've took some photo's.
When I take a multimeter and place it on the bottom two wires of the trafo I get zero rating. 
There is no difference between blue and red, neither does it make a difference if I change the wires in what ever way. Tried all possibilities I can think of.
Hello all,
I'm trying to hook this doorbell sensor up, what I've found is that when I connect it, I must connect it to NC. The downside is that when I reset the Arduino, the doorbell keeps ringing until pin4 is pulled up. How can I change that in the sketch?
Also I can ring it once, it rings and then it stops working. Connection to the gateway is lost and it won't ring either.
been trying to fix it for 3 days now, but I can't seem to figure out what I've done wrong.
Hooked up pin 4 to the input pin of the relay. The relay is directly powered by 5v coming from a usb hub with 2A.
The Arduino is powered using the same 5V, with a regulator to the radio to give it 3.3V. Connected a 4.7uF cap directly on the radio.
When I reset the arduino this comes to the gateway:
0;0;3;0;9;read: 16-16-0 s=255,c=0,t=17,pt=0,l=3,sg=0:1.5
0;0;3;0;9;read: 16-16-0 s=255,c=3,t=11,pt=0,l=16,sg=0:Doorbell Monito
0;0;3;0;9;read: 16-16-0 s=255,c=3,t=12,pt=0,l=3,sg=0:1.0
0;0;3;0;9;read: 16-16-0 s=1,c=0,t=3,pt=0,l=0,sg=0:
0;0;3;0;9;read: 16-16-0 s=0,c=0,t=1,pt=0,l=0,sg=0:
0;0;3;0;9;read: 16-16-255 s=255,c=3,t=7,pt=0,l=0,sg=0:
0;0;3;0;9;send: 0-0-16-16 s=255,c=3,t=8,pt=1,l=1,sg=0,st=fail:0
I can connect perfectly to the gateway using MyMQTT on Android so I think it is failing on the side of the doorbell any help would be greatly appreciated!