3D Printer (RepRap) Monitor - Part 1 - Introduction

My wife and I were sitting together in my office recently and as usual the 3D Printer was churning away.  Much to our surprise, and this has not happened before or since, the electronics stack started to smoke quite actively!  It turns out that one of the fuses at the top of the board had blown.  Puzzling as they are supposed to be self-resetting and they are not supposed to smoke to the point of flames!   It did NOT reset and it DID smoke!

In any case this was a little worrying, even without my wife sitting next to it!  I got an extra smoke alarm and installed it in the office but wanted to go a step further.   That step further was to design and build a circuit that would power down the printer on detecting heat or smoke.

Above is a picture of a prototype with all the components in place on the board itself.   I have chosen to use headers for the sensors, buzzer, LEDs, and the Arduino Nano though all or some of these components could be soldered directly to the board.   The sensors, reset switch, buzzer, and LEDs could also be mounted elsewhere with wiring back to the board.   It all depends on the implementation that is desired.

From the bottom right, and moving around counter clockwise, here are the elements of the circuit:

1. Pullup resistor for the temperature sensor
2. DHT-11 temperature sensor
3. Reset switch
4. Audible alarm buzzer
5. Green LED (behind buzzer)
6. Pullup resistor for the Green LED
7. Red LED (behind buzzer)
8. Pullup resistor for the Red LED
9. Relay
10. Arduino Nano
11. RS-232 monitoring connection
12. Relay connector (in my case triggers an ATX power supply but could switch A/C power with the right relay)
13. Gas sensor (I used the MQ-2 for smoke but other MQ sensors could be used for other types of gas in other applications)
14. Power connector 

More in Part II