Hey, I will help out where I can. This was a fun project that I built for a New Years' display several years ago. The main part not on here is the circuit diagram. I have all the programs in the zip file. It was written in the Arduino IDE. The wiring was 16 gauge on the relay side and on the control side, it is 36 gauge jumper wires. If there is more interest in this project I may try to clean it up and re-release it with a proper circuit board and circuit diagram. 

Ohh, I do like seeing something like this here.

Been building my own fireworks ignition stuff for a while. I ended up ditching relays because they are kinda slow and big. MOSFET work quite well too!

And regarding the output problem, you can actually multiplex the fireworks ignition heads. By adding a diode for each output and High- and Lowside-FET you only need 16 MOSFET and two 8-bit shift registers to have 64 outputs.

Then again... Relays just have a way more satisfying click to them <3 

I see everything for the the arduino(s) build, but what exactly is the mechanism to light the firework itself? The relays have to be hooked up to something to get the correct thermals to ignite, I don't see that specified. Thanks!

I added a link for the igniters. They are standard igniters and can be set off with anything from an AA battery to a 12v.