CTC Dual / Bizer filament sensor bracket

A replacement cable bracket for the CTC Dual printer to sense filament end-of-reel.
It uses optical sensors rather than microswitches. Search eBay or similar for "Arduino slot optocoupler'. As a sample advert (not a recommendation) https://www.ebay.co.uk/itm/161817129903

The sensors slot in to the bracket from the back and are held in place by being clamped to the back of the machine.

The idea is that they would be used in conjunction with an Octoprint Plug-in to pause when a reel is expended, or even to automatically switch extruders.

The trick to using these sensors is to fill most of the gap with something opaque, leaving only a narrow path for the light to pass through that can be blocked by the filament.
The cross-hole between the two arms of the sensor needs to be smaller than the filament to enable the filament to block all light. I used a 1.5mm drill to finish out the sensor tunnel after printing. Sensors from a different vendor might require smaller or larger ho