This started as a conversation about machines left running overnight and the associated risks. My machine is pretty much exclusively run unattended overnight and although it's in an outbuilding I started to wonder if there was a fire (or at least lots of smoke damage) risk from leaving it unattended. I still think the risks are pretty low, but for the sake of a smoke alarm and a few bits of electronics I had kicking about I thought it might be fun to build a fire alarm cutout device. Pretty much this device will sit inline and powered by the mains lead going to the BigBox. A standard smoke alarm with a relay output triggers the device to cut power to the printer via a spark-less solid-state relay. You can use either the type of low voltage smoke alarm designed to be interconnected (as per the box in the picture I'll attach in a moment) or if you prefer you could use a smoke sensor designed for a fire alarm panel. It also doubles up as a standard smoke alarm when the BigBox isn't in use and as a more convenient to access power switch/emergency shutdown button. Life keeps getting in the way so progress is glacial...So far I have built a little Bistable switch on a front panel PCB, mounted a little off the shelf 12v PSU and found a suitable off the shelf relay and smoke alarm. The bistable switch uses a 555, but if you want to build it out of a few transistors (or even one transistor if you are clever) instead that would do equally well, I just happen to have 555's kicking around with no use for them at the moment so I used a 555 Diagrams and a printable case design will appear once I have it finished and all working well. Usual caveats about working with Mains voltages apply.
Probably worth pointing out that there is an even simpler way of doing this with just the smoke alarm, power supply and a DPDT relay. But I didn't want a spark gap on a fire alarm type device (as if there are leaking gasses as as result of the fire then the alarm itself could cause a gas explosion). Also if you use the same workshop for dusty stuff then consider the ionising type of smoke alarm not the optical type I bought.
I used a smoke alarm module from ebay, and a nexa remote kit. Just hooked up the remote to the smoke alarm module. And attached one remote-socket to each printer.
Hmm nice solution, I wanted something a bit more hand-built than that but your way certainly is a neat way of doing it
Thanks, it's not going to win any awards for industrial design....but it'll do the job well I think. I'll put up a schematic and some links to the design files in case anyone fancies building one, but there is nothing revolutionary here...just a bistable circuit (of any kind) a PSU and a Solid State relay.