infrared wall to detect an object

Hi.

For a project that I'm building, I need an object detector that signals when something "cross" the virtual wall of light.

I create a virtual wall using a laser and two mirrors (one in front the other). The laser goes to the front mirror, it reflects the light back to the other mirror that is behind the laser, and it reflects back the light and so on. An the end, a photorresistor sense the laser light. When an object cross thru the light, the photorresistor change and a comparator signals that something is passing thru the virtual wall.

The problem is the photorresistor that it is sensible to natural light and of course the laser... it is dangerous for the eyes (an accident can happen). Another problem is with the mirrors, they need to be complete aligned to each other.

I want to change it to infrared light and a IR detector.. like those used in remote controls. But I need some IR leds with a small apperture to create a virtual wall.

Do anyone has some ideas, facts, experiences, suggestions and so on about what to do ? Is it a good idea ? Any led reference for it ?

Thanks

Hern=E1n S=E1nchez Medell=EDn, Colombia

Reply to
Hernán Sánchez
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I don't have any information on a IR emitter, but suggest you look at modulating the beam. By using a narrow filter on the detector, you should be able to filter out ambient light changes and use a lower power.

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Thad
Reply to
Thad Smith

.=2E.

.=2E.

ulating

o filter

I second that.

In school we built an infrared sender and detector, both running off 9V batteries, using a simple photodiode and a IR led. IIRC it was about 10kHz modulated, 1:10 or 1:20, and worked 30m in sunlight.

If you need it badly enough, I can dig up the schematics - although that could take some time.

Regards,

Phil

Reply to
Ph. Marek

I don't know what your application is, but if this is for safety, you might want to check out standard solutions. This google search might be helpfull:

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Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)
Reply to
Stef

Don't try to use mirrors. Use an array of transmitters and an array of receivers. Use different modulation frequencies for adjacent beams so that you can filter for the signal from the desired transmitter.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

use the phrases "light curtain" or "light grid" (German: Lichtgitter, Lichtvorhang) to get also non-safety products.

I design light grids for industrial application, e.g. for measurement, but not for safety (DUOmetric). Usually they are cheaper than safety products, and much more versatile.

Oliver

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Oliver Betz, Muenchen (oliverbetz.de)
Reply to
Oliver Betz

I agree. It sounds like you are looking at a standard light curtain. You give it power, and it will tell you when the aperature has been crossed.

Reply to
Noway2

Wow... thank you all. This is what I'm looking for... I will use modulation to filter out ambient light (this is a home made circuit so the industrial solutions are a good reference).

When you say the beam needs to be modulated, do you refer to send burst pulses of certain frequency (10KHz for example) ? A block diagram will be enough to understand it... I don't know if you say "filter it" using hardware or software (what does 1:10 or 1:20 means ?).

Thanks again... it's a great help all I'm reading here.

Hern=E1n S=E1nchez Medell=EDn, Colombia

Reply to
Hernán Sánchez

Hern=E1n S=E1nchez schrieb:

What I meant is "use pulses at 10kHz, with 10% or 5% ON time to get more current through your sender" (sharper pulses, same average power).

Regards,

Phil

Reply to
Ph. Marek
[...]

TANSTAAFL - if you want some speed, you need some bandwidth, and then you will detect also noise "not having the same waveform".

But at least you spread the spectrum by using the PN-sequence.

There are also other sequences with suitable properties. Finding the right one is "interesting", but depending on the application, the improvement might be small.

Oliver

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Oliver Betz, Muenchen (oliverbetz.de)
Reply to
Oliver Betz

Hoyt Engineering has developed just such a presence sensor which is not yet available for public sale. What I am able to disclose is that this sensor rejects noise orders of magnitude greater than the received signal, including noise transmitted by other such sensors. Response time is 20mS or less and total power dissipation is around 1 mA for a sensing range of 1-2 meters. Component cost is less than 5 USD.

I would be happy to provide you a solution in return for your honest application feedback. Please e-mail me directly to discuss further.

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Steve Hoyt
Hoyt Engineering
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Reply to
Steve Hoyt

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