Bit of sensor advice please

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ajcgkm

New Member
Hi iv just finished making a light sensor about an inch square that picks up a laser beam from however far away you can see it (with my eyes that's about 10 meters). What I want to do now is be able to detect an object instantly at a distance of upto 50 meters away.

So What are my options for sensors that can quickly detect that an object has passed in front of them.

The light sensor I made is very responsive. The laser Is controlled via a 2n222 from a picaxe that receives a input signal from a push button. The laser is on for a quarter of a second then the button signal is ignored for 3 seconds. So you have to be really accurate and a target of 1 inch is small from a long distance. So looking to pick up a larger target of about 5 inches. I can do this with ultrasound module but the range is only 4 meters so looking for what else is available to me.

I appreciate any input
 
premelec

premelec

Senior Member
something called a lens, or concave mirror to focus a wider area on your smaller detector... perhaps... [fresnel lens - don't let the sunlight get on it and
cook your detector..]
 
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John West

Senior Member
Your use of both Imperial and metric measurements leaves me a bit confused about how I should respond, so I'll just stumble along.

The cheapest way I've found to increase optical sensor range is an inexpensive plastic Fresnel lens. I've found them as large as 8 inches by 11 inches at dollar stores here in the US. (Less than a Pound Sterling.) The area of the lens provides an increase in gain of roughly that many times the area of the detector. Gain and range do not correspond directly (Inverse Square Law.) But about a 4 or 5 inch on a side Fresnel should work fine for your application.
 
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SAborn

Senior Member
What detector are you using, as a laser at 50m should be still a dot.

Have you considered using IR (infa red), i have commercial IR sensors that work to 30m and are very reliable.

What is it you want to do with the sensor application.
 
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Circuit

Senior Member
John West said:
Your use of both Imperial and metric measurements leaves me a bit confused about how I should respond, so I'll just stumble along.
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In the UK we are rather "bilingual" in our measurements. Our road signs are in miles; we buy electrical cable by the metre, cloth is often 54 inches wide but purchased by the metre length. Metrication has its limits and we tend to work with both systems in common speech, so we still "speak in imperial" as well as "in metric"!
 
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Paix

Senior Member
Not to mention the Mars lander that crashed into the surface.

We buy pints of beer and litres of Cola. speak of metres per seconds and miles per hour, but sometimes our offspring express alarm when feet and inches are discussed. It's a developmental thing and indicates where you were when different measures were more common perhaps.

Don't be confused about how you should measure, just tell us, we have the necessary experience to sort it out - I think. So give us the whole nine yards . . . ! (please)
 
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rossko57

Senior Member
Perhaps a little about how you envisage the object detection working - are you constrained to a transmit+recieve type unit in one place, or can you seperate them for a break-beam style setup? Is the target object reflective, or can be it seen by PIR sensors? Buried wire-loop detector? Can you fit a transmitter or a reflector to your object? Are you interested in objects that move, or just static presence?
 
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Goeytex

Senior Member
As Saborn suggested, the laser image should be a dot at 50m. However, cheap lasers could throw a larger dot.

I would suggest measuring the laser image at 50 meters. Then get a Fresnel lens a bit larger than the diameter of the measured "dot" and focus the image on the sensor. You should get a lens with as short a focal length as possible. See conceptual drawing:

An Alternative might be to get a better laser that makes a very small dot at 50 meters.
 

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techElder

techElder

Well-known member
I do know that if you rotated that beam exit point about 1/4 of an inch the targeted dot will move about 1 foot at 21 feet.

I think the Fresnel lens will be mandatory for calibration and each end of the system will have to be seriously permanent.
 
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Phil bee

Member
Are you trying to identifiy the size of an object or do you just need t know that an object is within detection range.
 
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Circuit

Senior Member
JimPerry said:
Confused enginbeers screwed up the Hubble telescope with imperial and metric :cool:
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Come on Jim, you know better than that! Stop spreading urban myths. The error arose from the incorrect assembly of the reflective null corrector in which a lens was 1.3mm out of alignment - nothing to do with imperial and metric I think, but simply an assembly problem - we never find assembly errors in our PICAXE projects, do we?:)
 
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Paix

Senior Member
The real truth was that it wasn't really so much of an imperial/metric screw up as a communications failure between the various software teams who should have been aware that the other was working in different units.

I have a universal stomach, beer and Cola go down well despite the different UOM.

We do buy our ice cream in litres and not gallons though! :)
 
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Goeytex

Senior Member
If we (USA) had adopted the Metric system like the rest of the world (like we were supposed to), the Orbiter accident would never have happened. Communication failures regarding Imperial / Metric conversions would have been a non-issue.

Our Congress cannot even pass a legitimate budget bill, much less a Metric Conversion Act. About all they can muster up these days is new ways to spy on folks. Sad to say but we will be on a mixed Imperial / Metric system for a long lime to come.
 
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ajcgkm

New Member
soz for any confusing on measurments just im either working with one or the other or strange as it may seem both. However it's irrelevant to the question.

Nuff said, so for those who want to know the application is for a mate who has taken up clay shooting but is a terrible shot so I made a simple laser targeting system.

Luckily I have got some red 6mm laser modules with built in driver from feebay. I also found out that the lens is adjustable on them and expand the lens. If I put a ldr and pot and use them as a voltage divider the output from them can b calibrated to what I want. Then the laser from around 20 meters away will hit the ldr upping the voltage lighting an led on the sensor indicating a hit. The laser will be pulsed quarter second from another 08m2 and then delayed for 3 seconds to give the illusion of firing. JUst got to make a pressure switch out of some conductive thread and the project is finished. So thanks for all the input and soz that I started an argument about measurements that led to some space mission failure. cheers AJ
 
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Paix

Senior Member
Hmmmmm. I think that you may improve your mate's pointing prowess, but live clays may live on as he fails to lead them for a knock down shot unless they hover for him. :)
 
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John West

Senior Member
About the only time we use the metric system here in the US (outside of scientific measurements and running sports measurements,) is when the marketing folks are trying to fool the masses, such as when they tell us in an ad that a car has a "powerful 2.2 liter engine," when all the nuts and bolts are built to the Imperial measurement scale, or "American" as we call it these days, even though the US is only a small part of the "Americas." (We don't care. We think we're tho only ones in the hemisphere who matter. :rolleyes:)
 
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