I have an Arduino microcontroller controlling my hot tub. There is a big contactor that turns on the heating element (230 VAC) and I'm sure some nice electrical spikes are generated. I've already seen it mess up the LCD display on the Arduino. The Arduino output is connected to an optically isolated relay which in turn energizes the contactor. I'd like to find out what I should do to protect my Arduino from electrical noise the contactor makes when it energizes and de-energizes. I'm building a PCB that the Arduino will plug into, so I could put some protection/filter circuits there. Any suggestions?