I have an 8 channel relay board (here's a link to the actual product (http://smile.amazon.com/dp/B00KT0E1RY/ref=sr_ph?ie=UTF8&qid=1463753455&sr=1&keywords=smakn+8+channel).
I understand how to hook everything up so that the inputs control the relays correctly, however I have one concern on my inputs.
I realize that this board may be designed more for arduino projects, but I have three different input devices (Axis Door Controller a1001) that have two outputs each of 12v. When one of the six outputs applies 12v, the corresponding relay activates the controlled device (in this case, electric door strikes).
My question: I noticed that on the input side of the relay board, there is only one negative terminal and 8 signal terminals. My thought is that the positive of the each input will need to be attached to the a signal port and the negative would get attached to the common negative. Will this be a problem with having all of the inputs negatives attached together? I know enough to be dangerous, but don't want to have issues if 12v from one input device is somehow interfering with the other devices because the negatives are all connected? I thought that it could be a good idea to have one relay board per input device (a1001) in case this might be a problem.