Dear friends!
I’m trying now to make a midi controlled jacob ladder!
So I started to make some tests to study the “viability” of the project before starting some crazy building…
Basically, I use a car coil ignition, driven by a IRF840 mosfet, with the Arduino I will PWM (using timer one interrupt) at the notes frequencies to get a electric arc to get the correct tone.
But I think the electric arc is transmitting a lot of electromagnetic power in the air, and I investigated some stuff… it should be an EMI/ESD issue… the LCD get totally nuts, the computer loss sometimes the USB conexion with the arduino…
I think there is some interferences on the data lines of the display…
I googled for solutions of this problem, people recommand to put 100uf and 100nf to the power pins of the display, of course, this resolved nothing in this case. Put a freewheel diode to the coil is useless because the output power of the car coil don’t produce electric arc…
I saw some special chips to remove interference and parasites on a data bus line, used on TVs and mobile phones.
As you can see, this chip is an aquivalent to a lowpass filter and transil diodes.
Do you think this can solve the problem? I am conscient of this is an HARDCORE problem 
and I will suffer to solve it
Here it is the normal LCD working
Here it is what I can see on the LCD display when the car ingnition coil is working
I tried to drive the display with shift-register and I2C, unfortunatly, I get the same interferences issues…
Actually i’m working with the LCD in 4 bits mode and D0…D3 are grounded.
The car ignition coil is drived with a circuit totally different as this one I use with the arduino and the display. The only they are commonly sharing is the GND, nothing more for the moment that’s why I think this is a radio-interference…
I hope you can give me some advices or some clues to solve this problem, best regards