Hi! I am working on a personal project* where I will have a small device on a persons work desk to check is the person is there or not. These are the requirements:
- I will have to build around 30 of these so the technique used can not be too expensive (around 5 dollar for this functionality is ok).
- The people will be in an open office environment and I would like to keep false positives from co-workers passing by behind to a minimum.
- If a person leaves the desk I would like to be able to tell after 30 seconds or less
- Some instructions on where and how to place the device can be given (e.g. this side should face you) but the detection range can not be too narrow so that false negatives are given
What I have now is a PIR sensor like this one (HC-SR501: cheap from china) But the range is too great, adding additional layers of plastic infront of the sensor helps but it get unreliable.
I have been thinking of ultra-sound but I am not sure the detection width of the standard HC-SR04 (link to sensor) is wide enough.
Anyway, I would very much like to discuss this with the bright people frequenting this forum if you have any input! And yes there has been much googling.
*Edit: The project will be used in a master thesis in ergonomics. The people in the study will be volunteers and we will follow ethical best practice.