Hi so I am working on a control interface for a lighting rig for my 3d printer that also powers a pi. Problem is I have to wait 90 seconds minimum before turning the lights on or I blow fuses. The lights and switches are 12v and I want my aurduino to detect when the pi switch has been thrown the light an led after 90 seconds to indicate it's safe to turn on the lights how can I do this and wire it up and code for it
When the switch is detected save the value of millis() to a variable. Then periodically check the current value of millis() and when millis() - savedMillis > 90000 it will be time to turn on the light.
Have a look at how millis() is used to manage timing in several things at a time
...R
Hi,
Why not get the Pi to do it all, seeing as everything is timed to it being turned on?
How many lights do you have?
Can you put them on their own circuit breaker?
If more than one can you switch them on in sequence to even the starting load current?
Tom... 
Sorry Geekmoto13 for jumping in on your post. I'm just learning myself and have questions for you.
What fuses blow? Fuses on the 3d printer or fuses that provide power to the wall socket?
I'm thinking you just need to split the load. Source the power to the lighting from somewhere else. Connect that source to the lights via a relay & turn on/off the relay from the pi. MAYBE?
No problem marine_hm. The fuses I blew were in the receptacle that's connected to the input side of the psu. To answer another question I have already split the pi and lights onto separate output rails from the psu the lights are on string about 9 sections at .5 amps total though when I turn them on. They spike over .5 amps. Not sure how far and what my pi is drawing both meters are having a few issues