This is a simple way to know you are out of filament, I´m using a momentary switch Cherry and I have uploaded the dimensions in case someone has a similar switch. The idea is to use an Arduino Attiny85 with a buzzer to make the alarm sound as soon as the filament is getting close to finish Here you have the video of the filament alarm working: http://youtu.be/QGUehV8nUc4 If there is anyone who wants the Arduino code for the Attiny85 you can let me know and I´ll be posting it here or in my blog. Also I have the Schematics and the layout in case anyone wants to make a PCB with the Attiny85 microprocessor. Here are the files: STL and the Arduino code https://drive.google.com/open?id=0B7dtMeeMPK5rfmE2WlctNEdWZkc1US1TTWFJblYyanJ1SExwczRtX1UyQjhJYTlqUlk2dUE&authuser=0 Attiny85 PCB and Schematics https://drive.google.com/open?id=0B7dtMeeMPK5rfm55TGxFMGdVRXlXcmVkd2I5WVJLcURFbjh3UjlXckNxdjhpYkNVQmd1QkU&authuser=0 The Attiny programmer Layout and Schematics https://drive.google.com/open?id=0B7dtMeeMPK5rfjgyemtrUUUxRTRSVHZNd0F1U3dLZ1JybXZFbzNkS0VYN2xQbnY4NjNobDg&authuser=0