Need an idea for car presence

[abicash]

Hello all

I am working on a concept.I need to sense the presence of cars parked in a parking lot.
This will be a 2 stage process where i have to sense the presence of a parked car and feed the input to a central server.Apart from that i need to also feed the size of the vehicle.It should be either "small" or "large"..How can this be achieved?
I was thinking of an optical sensor to sense the presence of the car but not sure of how to get the size from that.
Any pointers?

Thanks in advance

 

[cowana]

Can you put a coil of wire in/on the ground? The car going over it should change the inductance of the coil.

Andrew

 

[abicash]

Thanks for getting back Andrew

Yes that can be an idea.But how can that say about the size of the vehicle?

 

[colin55]

If you put 2 coils in the ground you can get some idea of the length and this will convert to size/weight.
The only problem is the height of the vehicle off the ground will also influence the result.

 

[abicash]

Hello Colin thanks for the feedback

The induction varies due to weight? or some other parameter?

 

[Gayan Soyza]

I'd use two industrial type IR TX & RX pairs near the gate & do a small direction detection code using a uC & detects the vehicle is leave or in.

 

[cowana]

The inductance varies due to a big chunk of metal being above the coil - it makes it harder to push charge in and out. More metal closer to the coil = higher inductance. However, as Colin says, while a lorry has more metal, it is a lot higher off the ground, so might give a lower reading...

Andrew

 

[Reloadron]

The following quote:

Inductive-loop traffic detector systems operate by sensing disturbances to the electromagnetic field over a coil of wire built into the roadway (Figure 1). When a conductive object (typically made of metal) enters the area over the wire loop, the magnetic field generated by alternating electrical current in the signal detector circuit induces weak electrical currents in the conductive object. (The AC frequency may be between 10,000 and 200,000 Hz, typically around 20,000 - 30,000 Hz.) The electrical currents induced in the object generate their own magnetic field that works in opposition to the magnetic field generated by the sensor coil (due to Lenz's Law). This opposition changes the resonant frequency of the sensor circuit by reducing the effective inductance of the sensor coil. This change in resonant frequency (an increase in frequency as the inductance decreases) is detected by the circuit instrumentation in the signal controller cabinet, which then tells the signal control electronics that a vehicle is present.

is taken from here. This should give some idea of using an inductive method. Along the same lines thing about a sensitive metal detector inverted and below the surface a few inches. Depending on the mass of the vehicle a rough estimate of size can be had.

Ron

 

[abicash]

Hi Gayan and Andrew thanks

Gayan: i had a similar thing in mind but was hoping if there was an easier way out

Andrew: Thnaks seems sufficient for the moment.Although this doesnt address for the size tracking of the vehicle

 

[abicash]

The following quote:



is taken from here. This should give some idea of using an inductive method. Along the same lines thing about a sensitive metal detector inverted and below the surface a few inches. Depending on the mass of the vehicle a rough estimate of size can be had.

Ron

thanks for the link Ron

 

[abicash]

Seems these schemes will require infrastructural changes,which may not be feasible in my current scenario.

 

[crutschow]

I think some sort of IR transmitter/sensor scheme would be the best way, but having to know the size of the vehicle complicates it. Do you need that because they charge according to the size?

 

[sound2man]

I'm a complete noob, but couldn't you set up two IR or laser sensors and have something calculate the size of the vehicle using the distance from each sensor?

Or you could set up a series of sensors on either side of the lane and calculate the distance according to how many beams were broken.

 

[bryan]

Too bad you could not modify the infrastructure. A load cell would probably accomplish what you need.

 

[colin55]

Apart from the cost of a load cell, how are you going to get a car to sit on the cell. It's hard enough for the Road Traffic Authority to weight trucks with a portable scale.

 

[ronv]

Park o meter

I'm not sure if you need to measure each parking place or only at the entrance. If it is a drive thru it seems like 2 ir sensors like what are used in tv remotes and tv's would work. Spacing is such that if both are blocked it is a big car. If only one at a time is a small car.

 

[abicash]

Thank you all for taking interest and replying on the topic

Well the load cell or some sort of strain gauge was my first idea but was promptly told that no infra changes would be done.

Then i thought about some sort of IR setup and that is on my priority list.

I am happy with the Inductor idea and in thought process how this could be accommodated.

Thanks

 

[abicash]

I'm not sure if you need to measure each parking place or only at the entrance. If it is a drive thru it seems like 2 ir sensors like what are used in tv remotes and tv's would work. Spacing is such that if both are blocked it is a big car. If only one at a time is a small car.

Ok you pointed out a thing which i failed to list..I need to measure each parking place not the entrance.So its a bit complicated than what can be installed at the entrance.

 

[colin55]

My idea is the cheapest with two sensors to detect the approx length of the car.

 

[abicash]

Hello colin

I think you are right.What kind of sensors would you suggest?And they need to be place horizontally? or vertically ? Vertical beam placement may damage the sensors as i think.

I have worked with IR universal remote application earlier and know stuff about IR remote protocols and more.

But this application needs just a beam which needs to be cut ;no intelligence,just digital.

What xmitter-recvr pairs could be available off the shelf?

i can buy them on farnell , digikey or mouser.