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.
I have also been looking at smarter IR sensors like the one used in this clip . I have not been able to iddentify the sensor used but maybe MLX90614 (link to sensor) would do the trick?
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.
I've done something similar in the past with visible light phototransistors.
Variations in ambient light or reflections from the victim kept retriggering the sensor until the person left, fell asleep or died.
My solution had a wide view, but could easily be 'choked down' with a tube of black heat shrink.
To set a reliable range of hysteresis, i used an 8-pin micro to average events over time to eliminate false triggering. It worked great. Cost less than US$3 each.
lastchancename:
I've done something similar in the past with visible light phototransistors.
Variations in ambient light or reflections from the victim kept retriggering the sensor until the person left, fell asleep or died.
This sound really interesting! I will PM you about more information. Thanks.
Grumpy_Mike:
I suspect that the bright people of this forum would find your project distasteful.
I think those people should not be so quick to jump the gun there. The application of this project is in ergonomics, its for a master thesis, all participants are volunteers and we follow appropriate ethical practices.
LarryD:
... Using a SR04 and coding things to have at least one measurement near by (example 3 feet) within a period of time should work. ...
I will try this, I have limited time and resources for experimenting in the actual environment though. Thanks
Yeah I read that but I didnt find any useful information.
How about this sensor: MLX90614 its i2c and it seems to be a similar sensor to whats being used in the Ben Heck TV Show. Does anyone have any hands on experience here?
You should be spending your time looking for a way to measure how productive the people are, not how much time they spend at their desks. That is bad management. They could be asleep at the desk!
PaulRB:
You should be spending your time looking for a way to measure how productive the people are, not how much time they spend at their desks. That is bad management. They could be asleep at the desk!
I will update OP to better explain the project purpose so that we may discuss the technical issues.
How about a thermistor embedded right under the fabric in the chair? Room temperature probably won't ever exceed, say 76 F. in an office, and when somebody plunks down in their chair, the thermocouple will probably read at least 90 F after, say, 2 minutes. Bring the thermistor wires to the back of the chair to hook to a Nano and a cheap little RF module. That might get your cost down to $5.00. Of course, be prepared for the smart ass who sets his warm coffee cup in the chair as he leaves the desk. Maybe multiple thermistors -- one under each cheek.