Door sensors used in elevators/lifts are very expensive and my budget is not that much. But I need a similar mechanism or solution to detect the presence of someone if he/she is standing in the given line where the elevator door closes.
I can't use a PIR sensor as it checks proximity and the range is very small and I need it to be around 5-6 meters. This means that the transmitter and the receiver will be 5-6 meters away from each other in a straight line so that whenever there is some individual standing at the given line, the receiver will not receive the light from the light source(transmitter) because of the obstacle between the transmitter and the receiver.
For eg, I can use infrared transmitter or laser source at one end and light-dependent resistor or light or any photovoltaic sensor to detect the given source light at the other end. So, when there is no obstacle the LDR reading in the range of 0-255 will be around 200 due to illumination from the laser source, but when there is some obstacle (the presence of some human/objects between the transmitter and the receiver), the light source will not be able to reach to the LDR side and the reading will be around 80-100. Hence, I can apply some logic or some LDR range to distinguish between the two situations - one without any obstacle and other with an obstacle in between.
I hope you are getting what I am trying to say. I really need help here as I am not able to get any long distance infrared source/detector. I want it to be invisible at nights as well ((means no humans could feel that there are sensors at either side of the walls/doors), so I can't use laser source. Any solution would be appreciated and any other approach to accomplish the same thing of detecting objects between the transmitter and the receiver will be a big help as well. Please let me know if you need any other information about the project.