IR Object Detection

[jnthn]

Hi Folks,

I'm measuring the speed of a small moving object using two InfraRed switches, does anybody know of an "InfraRed Object Detection Device" that can return data to a PC telling it if an object is present or absent.

Alternatively if anyone has a bit of knowledge of how to connect an IR Ranger to a PC and get data from it.

Kind Regards,


Jonathan

 

[dknguyen]

You will get more hits if you use the term "proximity sensor". Sharp MIcroelectronics has a bunch similar to the GP2D12 (except this is a rangefinder). To connect to this particular device to a PC you would need a serial ADC that goes into a PC...

Not sure if proximity sensors at the best thing to measure speed with, but then again, I don't know exactly what you are doing.

 

[jnthn]

IR Proximity Sensors

Hi,

Thanks dknguyen for your reply, here's my application:

I'm passing a box accross a conveyor at a speed, I need to know the speed at which the box moves accross the conveyor belt. So I put two Proximity Sensors at a measured distance apart, run the box, record the time that it passes the first sensor, then the second enabling me to work out how fast it the box moving. In reality all I need is an IR device to return a 1 or 0 whether there is an object or not.

Thanks

 

[Nigel Goodwin]

Probably the easiest method is to pass two IR beams across the belt, and measure the time between the breaking of them both.

 

[jnthn]

That's how it will work but I'm how to connect the IR Devices to a computer and get data from them. I don't think a "Plug n Play" device exists, and an IR Ranger or Proximity Sensor will require some kind of adaptor. Any ideas?


Thanks

 

[ericgibbs]

hi jnthn
As already posted, you require two pairs of IR transmitters and receivers, aligned at right angles to the objects path, spaced at some distance apart along the path.

If your object is carried past your IR transmitter/receiver pairs a at 'moderate' speed,[let us know, in say mtr/sec].

You might consider using the PC's parallel port input pins to get the IR receiver TTL signal into the PC.

The PC program would poll the port pins, get the TX/RX pair #1 signal as a start, read the PC's internal Timer at T1, then the TX/RX #2 signal to stop the timer at T2.

By setting the TX/RX pairs about 1 metre apart, along the path of the object, the 'speed' of the object will be directly proportional to T2-T1.

If you need a sketch let us know.

Regards
EricG

 

[jnthn]

Hi Folks,

I appreciate the responses, the sketch won't be necessary considering I have already built the aparatus (just to add a method of clocking the speed, of course).

My question concerns the connection between PC and IR Device i.e. type of transmitter&reciever, type of cable, type of connectors and any particular make or model of said hardware that ye can recommend.

Thanks again

 

[dknguyen]

Digikey has a lot of pass-through IR type sensors. It's somewhere in their catalog...I'm sure if you search you'll find them. How wide does the beam need to be and how far do you need to run the cables?

 

[jnthn]

Yup! Using a PC with Windows XP, the cables will need run for about 3 meters and the beams for 500cm. Having to work with wires and boards and stuff is out as I have little experience in electronics. The perfect solutions is an IR device with cable and connector(parallel/serial) already assembled. I had a look on digi-key but didn't find anything to fit that description, do ye think that such a device exists?

 

[dknguyen]

I think 5m is a bit high as far as the Digikey ones go, but I forget how far the longest range one is. let me look myself. It's easier with a catalog in front of me.

UPDATE:
Lonest range Digikey one I could find was only 39 inches and it cost $100. YOu might save some money by just making it yourself with a laser pointer, a reflector disk, and a filtered photo-detector sitting beside the laser (with all 3 sitting in a very thin triangle combination).

You could check out www.Keyence.com, but it's going to cost a bundle.
THis is a relevant Canadian webpage off the Canadian version of the website under compact laser sensors:
**broken link removed**

I think they cost $200+ though...

If you built something, it would be best if it was similar to the LVS-61 model where the laser and sensor are on one side and a relfective panel is on the opposite side.

Alternate names and terms are photo-interrupters, pass-through, and reflective and retroreflective laser sensors are also relevant.

 

[jnthn]

Ok, thanks a bunch for your expertise, I'll check the web with the alternate names you provided. However it looks like I'll have to use an alternate, less accurate method like a speed gun or something.

Thanks again for your time.

 

[ikalogic]

hello

am a mechatronics student, we work a lot on this kind of stuff.

here is a classic sensors arangement that can be used for the purpose you need.

Using a standard 38 Khz sensor (ambiant light ingnoring) you can easily reach your 5m requirement.

the sender is a high power IR led.

connecting all this the computer parrallel port would be very easy, and you don't even need a uController (those kind of sensors are TTL compatible)

good luck

 

[ericgibbs]

hi,
ikalogic has the right idea, use an off the shelf IR 38kHz pair. If you are on
a tight budget, consider re-cycling a old TV remote as the transmitter, they
will easily cover 5 mtr. Buy/find a suitable detector.

If the PC's printer port is already in use, you can use the two handshaking
input lines on the PC's serial port. Your input will need to be level shifted by a
MAX232 i/c, thats easy to do. The advantage is that the PC can be upto 30 mtrs away from the detector.

These objects, how are they transported thru the 'space' you want to
measure ?. Example, if they are a on conveyor belt and its driven by an
ac powered motor, the belt speed would be 'constant'.
Lets us know what the objects are and how they are moved.
One of us may have a better solution for your project.

Regards
EricG

 

[jnthn]

Hey Guys,

The objects are small boxes passed along a gravity conveyor belt(not motorised) at a constant speed.


How about two IrDa USB Reciever Dongles on USB Extension cables, they can be easily interfaced by my software.

Would an IrDa usb dongle be able to 'talk' to a generic TV Remote?

 

[ericgibbs]

hi jnthn
looking at your diagram my concern would be the accuracy of the system.
Depending upon the size of the object and its distance from the IR emitter
the 'apparent' speed would vary.

I appreciate that you could have the IR receivers close together, but that
would give you a very short object moved path distance.

I would suggest that you use two IR sources that produce two parallel
IR beams across the objects path.

Regarding the compatability of the 'tv' remote to the usb detector.
A tv remote usually transmits a coded burst of IR pulses, which are
repeated if you keep your finger on the button. The receiver decodes the
burst and performs the required action.

Have you any info/spec on the IR usb detector ?.

Why not carry out a quick test of the tv TX to your PC's usb RX

Regards
EricG

 

[jnthn]

Hi Eric,

The sketch is not to scale, you have a good point as the angle of the beam to each reciever is different, parallel beams with two transmitters would be more accurate. However due to pressing deadlines I think I will abandon the idea and just use a less accurate speed gun.


Thanks alot for all the help