Relays and SSR's??

I am looking into making a relay board for my Arduino. This board only needs to serve to switch on high current given a low current, low voltage signal from the Arduino. I would like it to be able to control a lot of things (have many terminals for circuits to switch). I am making a sort-of automated fireworks controller for a wedding. The relays (be they solid state of mechanical) need to be able to drive enough current to heat up some chromium wire, which is wire that when given a certian amount of power, heats up. This wire will light the fuses on the fireworks. For those of you that know about nickel-chromium wire, how much current/voltage will they need to heat up enough to light a fuse? I saw the intro on using relays here: (, and that gave me some idea of how to set it up. What relays will I need that are the least expensive, but are just strong enough to heat up the chromium wire? Can I use a TIP 120 (not 102) Darlington transistor? Also, I need some method of expanding the amount of relays I can control given the amount of pins on the Arduino. Do I use a shift register for that? Thanks for the support. :slight_smile:

One suggestion might be to use the nichrome wire fuses from Estes Rockets - (available in US hobby shops and elsewhere.)
These igniters are pretty efficient because they are coated with a powder that ignites easily and sparks a lot.
I bet a TIP120 with a 6V source would do it - but test.
Sounds like a fun wedding!

You could use a shift register, or an I/O expander, or come up with a trickier way of multiplexing.

595’s will do the job. The relays can handle the load you need to set-off a skyrocket, check-out light-bulb filament wire, 24v should be enough, perhaps less.

The link above is one array of 8 relays, the 595’s can be daisy-chained, so there’s no limit to the number of relays a single Arduino can control.

I’ve always wanted to play with fireworks via sequencers and digital input, so it sounds like a fun project - let us know how you get on.

Ok. Sure, I’ll keep you all updated. So…what would be easier to use, a 595, or an ‘I/O expander’? I have used 595’s before, and in m opinion, they’re a little complicated to operate (all that ‘shifting’ gets a little complex). And about the triggering mechanism - can I just use the method mentioned by BroHogan; use a TIP120 hooked up to like, a 6V lantern battery, and use THE TIP120 ONLY to ignite the wire, or do I need a TIP120 AND a relay, or just a relay, or…?