I have a large project where i'll be using more than a dozen arduinos, electromagnets, motors, LEDs etc. Most of them will run on 12v, and for practical reasons i want to use a single, large 12v supply for all of the electronics. I know that's generally not a good idea and learned the hard way that electromagnets might create current spikes that will reset the arduino or give false readings to the pins.
That would be a pretty disastrous occurrence, so is there any reliable way to filter out these spikes?
Are some power supplies reacting different than others?
Hi,
Power your controllers off a dedicated 5V supply, and bypass, bypass and bypass all your power supply wires at regular intervals.
Keep your 12V power wires away form your controller 5V power wires.
Keep your input and output wiring to and from your controllers away from the 12V wiring.
Can you post a basic block diagram of your power and I/O connections?
If not then;
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
How are you interfacing your controllers with the input and output devices?
Thanks.. Tom.. 
TomGeorge:
Hi,
Power your controllers off a dedicated 5V supply, and bypass, bypass and bypass all your power supply wires at regular intervals.
I was planning to supply the controllers with 12v. Would there be any advantage to using directly 5v besides the heat loss?
TomGeorge:
Keep your 12V power wires away form your controller 5V power wires.
That is impossible.
I don't think i mentioned, this is for an escape room project. There will be a central panel in the middle - all the power will be running from here, and up to 15 arduinos spread around in a 22 square meter space, so the technical space for the electronics will be very limited. All the wiring will be concealed in the decor, so the priority is to use the least amount of wires. More than that, i will have to run the wires together where possible.
This is largely still in the planning phase, so i don't have a diagram.
TomGeorge:
How are you interfacing your controllers with the input and output devices?
The inputs will consist of sensors and switches connected to the arduino input pins. I will try to keep these away from the 12v wiring.
The outputs will consist of electromagnets, led strips, electrovalves controlled using mosfets, and maybe some motors controlled with drivers.
The communication between the arduinos and the central system will be wireless, so the only long and overlapping wires will be the 12v and the audio cables.
With that much "stuff", at one piece will not be working properly at any time. You need to design in automatic self testing to occur at regular times.
Paul
Paul_KD7HB:
With that much "stuff", at one piece will not be working properly at any time. You need to design in automatic self testing to occur at regular times.Paul
What do you mean by that Paul?
I already have a game set up like that, and it's working properly.
The difference is that i used individual power supplies. That was a poor design choice, resulting in a lot of cables, power supplies and 220v sockets, making the technical spaces crowded and hard to service.
So my question was about how to reliably use a single power supply.
So my question was about how to reliably use a single power supply.
The answer is decoupling.