Ultimaker 2 Filament Sensor

The Ultimaker 2 Filament Sensor detect problems with feeding filament, such as skids, filament distance and a stuck of filament.

The hardware is printed and the electrically parts are standard components.
Everything you need is:
2 * half usb cables, ~1m, male
6 * screws 3x7mm
3 * transmissive optical sensors (TCST 2103): http://www.produktinfo.conrad.com/datenblaetter/175000-199999/184250-da-01-en-GABELLICHT_TCST_2103__VIS.pdf
and some resistors (150, 330 and 3*3k3 Ohms worked for me)

The dual optical measurement of the filament sensor detects also the direction! How the sensor does this? With a X4 encoding described here: http://www.dynapar.com/Technology/Encoder_Basics/Quadrature_Encoder/

Hack: fix a elastic band onto the roll, so the filament does't slip.
Use the standard ultimaker's 2.85 mm filament as a more robust axis.