I have an arduino mega based irrigation controller that takes 24VAC to power it.
The 24VAC powers solenoid valve and also goes through a bridge rectifier, filter cap and DC to DC converter module that supplies 5V for the electronics.
The arduino and electronics seem to work flawlessy.
However when I plug the USB cable into the Arduino Mega simultaneously with the 24VAC power supply then it causes the PC or laptop to play up.
My PC won't wake up after going to sleep - I have to disconnect/reconnect the PC power chord and reboot it.
At one stage the power on my laptop cut out and I had to re-boot that.
So I presume there is some noise coming though the mains power that is not being filtered out and is interfering with the PC/laptop electronics though the USB cable.
So my question is what do I need to add to PCB to prevent this from happening?