Hello friends!

--------------------------------------------------------------------
My overall philosophy here was to create a fire safety system that could be set up easily by anybody, with no programing, arduino, or soldering skills required. Everything is plug & play here. You just have to print the parts, download the code, load it on the arduino board, plug the sensors as indicated in the code, and you're good to go. The only tricky part is the modification of your printer alimentation wire, but this can be done using a simple cutter.
If you want a more complete system, don't hesitate to check up this creation:
https://www.thingiverse.com/thing:2432366/files

--------------------------------------------------------------------

I recently released my old version of Prusarduino, that I use to have on my old and nice Prusa i3 Hephestos. I just bought a wonderful Prusa i3 MK3 (with an heated bed of course), and thought it would be great to upgrade the fire detection system to fit this new printer. Here is my last version.

As a short video is always better than a long text, you can see what it does here: https://youtu.be/GDM_EfoJHiU

So, basically, it does the same thing as the previous version: If the temperature of the air surrounding the printer is over 75°C (in this case), or if some smoke is detected, the Arduino board switches off the 5V relay, and the printer power is automatically shut down. So, if anything starts to burn on your printer, any electricity is removed from it to avoid overheating. This new version fits the Lack Enclosure released by Prusa recently. :-)

I miniaturized it, with an Arduino Nano, in order to make it more affordable :-). This new system cost me 10€ on eBay! It's pretty easy to build, no need for programming skills, everything is enclosed here.

This new version has an improved temperature sensing range (-40°C to +80°C, thank to the DHT22 sensor). It will be more compatible with heated bed. However, be careful if you use it inside an enclosure. It can be really warm inside, and you risk to accidentally shut off the printer power while printing. It still uses the MQ2 sensor for smoke detection.

To act on the printer, I chose to directly cut in two the printer alimentation cable and wire it to the relay. This fix is not heating up while printing, I checked. So no risk there :-).

It requires these pieces:

MQ2 Smoke Sensor (link)
DHT22 temperature and humidity sensor (link)
5V Relay (link)
An Arduino Nano board (link)
/!\ The sensors can be mounted on different circuits depending on where your ordered them. In that case I'm afraid you will have to design a new case for them. Refer to my pictures to see the version I used. The links I attached are the one I used to purchase the devices. I do not have any relationship with the vendor, or earn any money if you buy them from there. So if you find a cheaper version, please go ahead!! :-) I just found more convenient to provide some links, as I had some trouble to find the good components...

Useful tricks:

All the instructions concerning the Arduino part are in the .ino file (Arduino script) that you can download here). You'll find how and on which pin to connect the sensors to the Arduino board. You'll also be able to change the parameters of the script, including. the temperature threshold, the delay before to power on the printer when the Arduino is started, etc.
Be careful, the MQ2 sensor can also detect some hairspray or isopropanol (when cleaning your PEI bed)... Don't spray some close to you printer, otherwise you won't be able to power it on for a while.
If my sensor cases do not fit perfectly your sensors, you can adjust them slightly using some pads for furniture that you can buy for nothing almost anywhere (see my pictures)
I added the .step files for those who want to modify the design. You should be able to open it in Fusion360. :-)
I hope you’ll like it. Please don’t hesitate to share some pictures if you make one.

Happy printing!!

P.S. If you like the design, please consider a small tip. It would help me buy PLA to test my designs :-)