Noob PCB layout question

Discussion in 'The Projects Forum' started by guitarguy12387, Jan 29, 2010.

  1. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
    Hey everyone,

    Doing my first pcb layout and i've got a few questions.

    The circuit employs a microcontroller to control some relays which, in turn, control some audio circuits.

    The microcontroller is a standalone unit that is not part of the board that i'm laying out.

    So basically, i am using some digital i/o pins from the MCU to connect to my board. These signals drive some transistors which drive the relays (which ARE on my board).

    Okay. Thats the background. I am wondering if i need to take any particular precautions when laying out such a circuit. That is, should i keep all the signals from the controller on one layer? Is it okay that audio traces run near controller traces? Is it okay that audio traces cross controller traces that are on a different layer? Grounding issues? etc, etc...

    In essence, what do i need to watch out for?

    Any tips or advice would be GREATLY appreciated.
  2. SgtWookie


    Jul 17, 2007
    You gotta keep 'em separated.


    If you have audio, controller, and power signals all on one board, you'll have to be careful. Having digital signals near audio signals is like inviting a punk band to play in a library. :eek:

    I'd use optocouplers/optoisolators from the uC board to control the power transistors that switch the relays. Be sure to use reverse-EMF "flywheel" diodes across the coils of the relays. Sprinkle 0.1uF poly caps between power and ground planes liberally to keep things more or less quiet.

    There are lots of tips and design standards available for reading here:
  3. guitarguy12387

    Thread Starter Active Member

    Apr 10, 2008
    Hehe yeah i figured so! The controller is on a different board by itsself. So the only thing i have going to the 'audio' board is the digital signals from that to the transistors for the relays. I have the transistors sitting on the edge of the board.... you think that would be okay to do? That way, the only digital signals actually on the board are right next to the transistors?

    Will do! Got the diodes in place.

    Why the optocouplers?

    thanks again