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Fire-Stop Smoke Alarm for 3D Printers

by digimatic, published

Fire-Stop Smoke Alarm for 3D Printers by digimatic Dec 3, 2016
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2575Views 226Downloads Found in 3D Printer Accessories


A Smoke Alarm and Remote Power Switch for 3D printers.

Provides a convenient wall mountable On off Switch for Printers such as the E3D that have a poorly positioned power switch.

Interfaces to a Smoke Alarm or Smoke Detector and cuts power to the printer if smoke is detected.

Smoke alarm functions as a regular Smoke alarm when printer is powered off.

Schematics and BOM to follow.

Print Settings


E3D Bigbox










Simple print, holes do not require infill, watch for warping on first layers.



Look I'm only going to say this once, this project uses MAINS electricity (which depending on where you live is somewhere between 110 and 240v). It has to switch the LIVE feed of your printer, if you aren't experienced with working with MAINS voltages then PLEASE do not build this yourself, or give it to someone experienced to check before you plug it in.

Doing this badly may cause electrocution or a house fire, if in doubt please move on.

Bill of Materials

Smoke Alarm with relay output:

Recommended: Aico EI105R
eg: https://www.amazon.co.uk/gp/product/B003XN4RRI

Note if you do lots of dusty things like sawing/milling etc in the same space as your printer go for the Ionising version which is less sensitive but not so easily damaged by dusty environments
eg: https://www.amazon.co.uk/Aico-EI100R-Powered-Smoke-Alarm/dp/B003XN4RPA

Main Box:

2 of of GX12-4 4-Pin 12mm Aviation plugs 12mm Female plug Male chassis socket
eg: https://www.amazon.co.uk/gp/product/B00X77GNAE

1 of ASH-10DA 10A single phase solid state AC relay 3-32v trigger voltage
eg: https://www.amazon.co.uk/gp/product/B01M074Z1P

1 of PSU PCB MOUNT 12V, 0.4A VCP05US12 (works for 110 to 240v input)
eg: https://www.amazon.co.uk/gp/product/B00DLSL1EC

Assuming your printer has an IEC mains socket, a Male to female IEC lead.
eg: https://www.amazon.co.uk/C2G-Computer-Extension-IEC320C13-IEC320C14

Control Panel:

2 of 2.54mm pitch prototype board (stripboard) 50x70mm (or cut to size)
eg: https://www.amazon.co.uk/sourcingmap-Prototype-Veroboard-Stripboard-50mmx70mm/dp/B00HR6IK8O

1 of LM555 Timer IC
eg: https://www.amazon.co.uk/Single-Timer-Dual-Line-Package/dp/B00B2IIA3S

2 of 10k and 2x 560ohm 1/4w is enough.
Just buy a kit
eg: https://www.amazon.co.uk/Saver-Resistor-Different-Resistance-Assortment/dp/B01KUEZIXE

2 of 12x12mm PCB push buttons
eg: https://www.amazon.co.uk/TOOGOO-Quality-Momentary-Tactile-Button/dp/B00MN91TD8

1 of Red and 1 of Green 3mm LED
eg: https://www.amazon.co.uk/Green-Yellow-Assorted-Emitting-Diodes/dp/B01F0TCXSW


A handful of short (5mm) M3 and M2 screws

2 x 4 core cable, USB cables of the right length for the control panel and smoke alarm are perfect…just cut off the ends

Solder, Hookup wire (or TC wire) for prototype board

heatshrink (recommended but not essential)


Soldering Iron
Drivers for M2 and M3 Bolts
HeatGun (recommended but not essential)
Wire Cutters
Multimeter (recommended for fault finding but not essential)
12v DC PSU (recommended for testing control panel but not essential)
Craft Knife (to clean up holes for buttons in front panel)

BOM Notes:

Not specifically recommending Amazon here, there are cheaper places to get this stuff, just used UK Amazon links for ease.

If you want to save money then use a plug in 12v wall wart style Power Supply from an old Router or something, aside from the Smoke alarm the PSU is the most expensive bit ! If you do that shout and I'll do a modified case to omit the space for the PSU. It's just more untidy that way as you need a separate power socket to run this (rather than it using power from the printers Power lead)

Nothing is that specific, if you use alternate equivalent parts it will likely work, but for the relay you may find the screw holes don't line up. The only critical things to fit the prints are the Aviation connectors, The 12mm PCB buttons, and the screw holes are perfectly positioned for the prototype PCB's I am recommending here (though you could cut regular stripboard to fit just as well)

Control Panel

Taking the Parts from the Control Panel section of the BOM above.

Assemble as per the schematic image included in this project, paying attention to the physical pinout of the LM555 as per datasheets and the polarity of the LED's.

Solder the 4 pin (USB cable) to the circuit with the colours as indicated in the schematic

To test panel apply 12VDC to the Red cable and Ground from your PSU to the Black Cable

If Panel is working, the green LED (LED1) should light and stay lit when the On button is pressed and released.

Then if the Test/Off button is pressed the Red LED (LED2) should light momentarily and the Green Light should go out.

Check the Output on the Green wire, this should measure 12V after the On button is pressed and stay at 12V until the Test/Off button is pressed when it should drop to near zero volts.

Check the White trigger wire from the Alarm.

When the Panel is on (Green LED1 is lit) if the white wire is touched to the RED wire then the Red LED2 should momentarily light up and the Green light should go out.

If these checks all pass then the panel is working. Solder one of the Aviation Plugs to the end of the cable paying special attention to the numbering of the Pins (they are numbered on the aviation plugs if you look carefully near the pins)

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Awwwwwwww yeah!

Been waiting for someone smarter than me to build this! Looking forward to the BOM / instructions.

Thanks I'll try and get it all over to you as soon as I can :)