Hi All,

When I go to bathroom, and there is auomatic machine give out the tower paper once I put my hand near to that machine. Does anyone know how it work? or any circuit relate to that?

Thanks,
Kevin

 

Most of these units work by using reflective infrared sensors that when the emitted IR light is reflected back off of a person's hands, the dispensing motor is triggered to run for a predetermined hand.

hgmjr

 

Thanks, hgmjr for reply. It does not call motion detection? How come it not detect too far. I have seen only work once very nera the unit.


Kevin

 

That is on purpose since you want to avoid triggering the towel dispensing whenever a person just walks by the dispenser on his way to the bathroom facilities.

hgmjr

 

Do you know, if infrared sensors detect about 20 inches far?

 

As a general rule, reflective sensors such as the type used in the paper towel dispenser have a limited range. That is because the sensor relies on the transmitted signal being reflected from a surface that can vary widely back to the detector.

The range can be boosted by using multiple IR emitters together with a detector circuit that boosts the incoming signal. Still 20 inches would requires some fancy circuitry to carry off.

hgmjr