System for determining occupied seats in an auditorium [closed]

Question

I need an app that can do live monitoring of whether each seat in an auditorium is occupied, so visitors can load the app and see where to sit.

The auditorium has a relatively flat ceiling 4m high, and the seats are .5m wide. The hardware cost per seat needs to be $5.

I'm looking for all solutions. Web cams, preasure sensors, sonars, lasers, arduino, pi, intel edison, anything.

Obviously there cannot be wires that people could trip over. Sensors on the ceiling could have wired networking. Sensors on the seat or floor would need to have wireless communication. sensors on the ceiling would need to consider occlusion by people sitting in the seats (think, if there is an empty spot between 2 people, can the sensor see it as empty)

In the end, the data needs to be collected as a simple list of which chairs are occupied/open

Possible solutions:

• rasberry pi's on the ceiling every 8 seats with a camera.
• pressure sensors under chair legs wired to pi's gpio
• Drones flying around the auditorium :)

Any ideas?

Update (more constraints):

• auditorium size is 400 seats
• Installation costs should average 10 chairs per hour(400/10 = 40 hours)
• as the picture shows, chairs are cushioned
• regular maintenance should take no longer than 30 min. per 2-hour event(eg, batteries)
• hardware should last 100 sessions
• for auditorium cleaning, it should be possible to "disconnect" and "reconnect" the chairs with 4 hours of labor.

Answer 1

OK, so the hardware cost per seat is $5. But what is the total cost per seat? What's the total cost for the whole auditorium? In short, what's your budget? Who will maintain this system? What other constraints do you have?

A simple pressure switch can be made for 50 cents, but wiring it might cost $100 per seat, so you meet the hardware cost constraint, but may fail elsewhere.

That said, with what little you've told us, the simple solution is to put a pressure plate on each seat, with sensor wires going down into the floor. Then all those sensors can be read by a single computer with a lot of input channels. That could easily be built for a cost of $200 + $5/seat, but I suspect that the installation costs will kill you.

If you want wireless communication, now you have to deal with how to power the thing. Who will make sure all those batteries are working every day, or will they all be changed out at a fixed time?

If you use one each of those cheap wireless transmitters and receivers in each seat and a small microcontroller to implement a poll/response mechanism, a battery, sensor and an enclosure, then you might just scrape by for $5/seat in volume.

Answer 2

Computer vision would work, but have some error margins like people putting a bag on the other chair. It may be uncomfortable to the people too to, although the cameras could be hidden.

Pressure sensors could suffers from a high weight bag too, where computer vision is more affected by area.

It's a fixed installation with a cost for that. When you can, use wires! There's then no batteries to worry, no signal problems, no RF pollution, and goes on.

As you have a relatively high number of seats, just use a small uC from Microchip, Atmel, or what you prefer, that should cost near 1,60 and a differential driver (RS-485 compliant), and use it to read lets say 4 seats sensors. Pass a bus of RS-485 (UTP with 2 pair), and poll the sensors.

EDIT (as OP said that has no way to pass wires in the floor)

If you go to computer vision^{note 2} and you said a chair occupied by some object will in fact by considered occupied (and not the say the people to put the bag on the ground and allow space for another people), computer vision could do the job. Just think its not that cheap as you may think.

Lets take a 200,00 camera (it should be higher than this, need to check prices and options on your country), thought 20 seats, so 10,00/seat would be more than you can use. You could get a larger area depending on the height of the camera relative to the chairs, but high angle lens does not seems a good option as there will me much distortion.

Wiring would have near more or less the cost of the other option. As the cameras require each cable from the hub/switch to the camera, a bus would not be feasible like an RS-485 bus.

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^{Note 1: You mean nothing of infrastructure for wiring, if there's no way to pass wires, then yes, you should go wireless.}

^{Note 2: For computer vision the better is to use RAW cameras (without image compression) and if it's unavoidable to use compression, at least H.264. (An lossless compression would give the same uncompressed image, but that's not easy to find). Good optics are very important too, so good focus. As you have a controlled light environment, sensor size could be less important, but not forgettable. Computer vision is not that easy, that's why some projects fails. Just putting any camera with any lens would not to the work for most of the scenarios.}

Answer 3

You are looking for an easy cheap solution. I doubt there is one. Each easy solution can be fooled. A camera is going to detect a jacket of bag on a seat, a weight or pressure sensors will get tripped many times. What if a person "takes" a seat them walk around. How does your system know a seat is reserved.

I think this system will need to use multiple sensors and some "rules of thumb" to make guesses. You will have to accept that the results will not be perfect.

Star with pressure sensors. You can wire an entire row together from seat to seat without creating any wire s on the floor. Then you have boxes mounted on the seats nearest the isle to handle that row. These boxes will need power. You will need to run wire down the ales to each isle box.

I would back this up with another system perhaps based on vision.

Then you can also count people and cross check the totals from the count, pressure and vision systems.

OK, one last question? Why do you care about the cost of the seat sensors. That will be trivial compared to the engineering and installation costs.