Can this design cause any problems? I'm planning on switching 75W (220V) loads with this relays. I'm using 10 such relays and terminals (HB9500M). Note that it's highly unlikely all of the relays to be active at the same, even if they do, it won't last more than 2 seconds. I'm also planning on soldering wires with the PCB traces to improve current capabilities. PCB is using 1oz traces. As you can see, small red trace is controlling the relay, which is controlled by ULN2803. Can this switching induce unnecessary noises in the MCU? BTW all relay loads are resistive.
When switching the mains (230 VAC) to a load your most important concern is:
How long will the relay's contact last?
Each time you switch the mains, the energized contact of the relay will create a small electric arc in the air that goes to the non-energized contact. That arc shortens contacts' life.
To prolong relay life you might want to buy relays with silver plated contacts:
There's another and I think more interesting idea to prolong contacts life. It's called "zero crossing relay switching"
Switch the mains when the 230 V voltage crosses the time axis. Take a look at this Microchip application note:
Just general comments:
- Line up each relay with its terminals for aesthetics and ease of debugging.
- Make the blue traces come in vertically to the common pin to maximise clearance between them and the coil pins.
- Move the red traces onto the bottom of the board. You have not need to move them to the top. That will keep all the mains voltages on the bottom and avoid electric shock to probing fingers.
- As pointed out in the comments, you should switch the live wire, not the neutral.
- Consider the use of one or more fuses.
- 75 W at 220 V is about 1/3 A. You should find a decent trace width calculator on line to work out this for you.
- Your live and neutral terminals have an unnecessary dance around each other. This brings the Line trace close to the edge of the board and unsuspecting fingers. Connecting the common to the neutral input solves that problem.
- You have plenty of space so you can use much wider lines from the ULN2003 to the relays.
Regarding the actual question, it's unlikely that you'll see noise on the CPU from the switching.
Have fun, but keep it safe!