Hi, I am looking forward to design a PCB where I can hook up 8 relays, and drive them by using ULN2803 & my PIC.

I tried on the internet and looked up the datasheet as well which left me with slight uncertainty, which is that do I need to place a resistance between the PIC & the input to ULN2803?

Datasheet says the base input already has a 2.7K built in. I just want to reconfirm if I need one externally also.

My circuit will be simple : (Planned circuit) - Port Pin -> ULN2803 input -> Relay ground (i.e. relay gets 12V common - every output of ULN2803 will be connected to the other point which will ground the 12V)