Need advice on what sensor to use to detect object

[black_wing_diaz]

Hi,

I am doing a project on reserved parking lot monitoring system & I will be making a model lot & using a model car to simulate how this system works. When a car parks at the parking lot, a sensor mouted in the center & on ceiling above the model lot, will detect the model car trying to park the lot. I am not very sure what type of sensor to use & where to buy it. I attach a picture with the dimensions of the model lot. Can ayone help me? Thanks in advance.

 

[Optikon]

Hi,

I am doing a project on reserved parking lot monitoring system & I will be making a model lot & using a model car to simulate how this system works. When a car parks at the parking lot, a sensor mouted in the center & on ceiling above the model lot, will detect the model car trying to park the lot. I am not very sure what type of sensor to use & where to buy it. I attach a picture with the dimensions of the model lot. Can ayone help me? Thanks in advance.

The real implementation will need to sense distances of a couple of meters right? From top of smallest car/motorbike to the ceiling which is a couple meters higher up yes? That rules out alot. Ultrasonic might be able to work at that range. Sounds expensive for an entire lot fitted with these things.
Why ceiling? why not in the deck like sensors do at traffic lights? inductive loop or RF under the vehicle? Or weight sensor?

For just the small scale model, you could use ultrasonic at up to a few feet range or even IR for smaller distances (& probably the easiest to get working the web is full of design examples, go look)

 

[black_wing_diaz]

Thanks for your suggestions, Optikon & I really appreciate it. I would consider ultrasonic sensor as IR may not be able to detect the model car. If I am not wrong, IR dectects heat emitting from the human, having a skin temperature of about 93 degrees F, radiate infrared energy with a wavelength between 9 and 10 micrometers. Therefore, the sensors are typically sensitive in the range of 8 to 12 micrometers. I am using it to detect a model car and I don't think that it may radiate any infrared engery, so IR may not be applicable. Also, u suggested inductive loop for the real implementation & I think it is a very good suggestion. But I am not sure whether any vendor is selling it.

 

[Optikon]

Thanks for your suggestions, Optikon & I really appreciate it. I would consider ultrasonic sensor as IR may not be able to detect the model car. If I am not wrong, IR dectects heat emitting from the human, having a skin temperature of about 93 degrees F, radiate infrared energy with a wavelength between 9 and 10 micrometers. Therefore, the sensors are typically sensitive in the range of 8 to 12 micrometers. I am using it to detect a model car and I don't think that it may radiate any infrared engery, so IR may not be applicable. Also, u suggested inductive loop for the real implementation & I think it is a very good suggestion. But I am not sure whether any vendor is selling it.

IR is commonly used for obstacle detection in robot/mobile applications. Generally, obstacles do not radiate IR (other than blackbody due to their temperature) The thing to consider is whether or not your models will reflect IR and not absorb or brutally scatter it. If they can reasonably reflect it, you can "blast" it with modulated IR and have a sensitive reciever tuned to detect that modulation. This drives some kind of a trigger that would indicate the presence or absence of your target (the model Car)

 

[black_wing_diaz]

Thanks again.....Maybe I need to do some experiment on this IR sensor. Its a pleasure to have your assistance.

 

[black_wing_diaz]

This is how the system looks like.....but I am not sure whether the sensor(SRF04) will be able to interface with a PLC(Omron CPM1A). Also, I dun know where to connect the trigger. I am using PLC because I have no knowledge on microcontroller & i dun have time to pick it up now......

 

[panic mode]

interfacing SRF04 to plc is quite difficult. not much because of signal level
but because of timing. since you are using plc,
i would recommend industrial sensors. maybe small photoeye
will do the trick? you could place piece of reflective tape on the floor
and put something like E3Z-R86 overhead like in your drawing.

 

[black_wing_diaz]

interfacing SRF04 to plc is quite difficult. not much because of signal level
but because of timing. since you are using plc,
i would recommend industrial sensors. maybe small photoeye
will do the trick? you could place piece of reflective tape on the floor
and put something like E3Z-R86 overhead like in your drawing.

Thanks for ur info.....U mean difficult because of timing but can it be done?

 

[panic mode]

difficult <> impossible

read the spec of the sensor. do you know how to match levels?
after this is done, you have to look at timing. (read the spec again,
there might be need for external circuit to match the timing too).

then read the spec of your plc. you will see that i/o is slow.
inputs usually have response of 5-10ms. outpus are
also limited b scan time which for plcs is in the ms range too.
high speed inputs are optional. most small plcs come with few
fast inuts (2-6) which are suitable for counting for example.
they are NOT suitable for much more since the plc logic is
normally scan time limited. doing more than that is possible
but it requires advanced skills (interrupts just to name one,
direct i/o access etc.). most people working with plcs for living
would find it way to dificult. you WILL BE over your head, trust me.

this sensor was designed to be used with MCUs. if you want to use PLC,
use sensors that work with PLCs. the one I mentioned costs similar to
SRF04, it's 10 times smaller (ok, it's 8x smaller) and it's 10 second job to wire it to plc.

 

[black_wing_diaz]

Hey Panic, many thanks. You suggestion is invaluable & I really appreciate it. I am glad that you have cleared my doubts. See you around.

 

[panic mode]

great....
note that you can use ANY industrial sensor if the voltage and polarity match the plc inputs.
i mentioned e3z simply because it's small, cheap and same brand as your plc so you should have no problem finding it.

 

[santosh reddy]

hi can u plz help me with the design of ultrasonic transmitter and receiver for object detection. i m doin almost the same project .here i have 2 detect a precence of car in a parking lot but i have problem with the transmitter n receiver design.if u have any circuits related to tht plz help me out .

 

[Super_voip]

Most car detection (in the real world) is done by inductive loops, for a scale model you may be able to use hall effect devices. Have multiple units at the entry to the parking lot and as the car passes over each one your unit builds a (magnetic)picture of the car. As each car would be a different weight due to different amounts of steel used in body, engine etc. this could constitute a signature. Then all you have to do is track the vehicle, or maybe have a simplified version at each lot.Military sensors include a piezo electric cable system which is able to determine number of wheels and cylinders in road traffic.