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LASER RANGE FINDER! HELP!

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erique82

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I just received a project from my professor, asking me to design a simple prototype laser range finder. This product uses laser technology to calculate the distance from the user to an object or location. Now, these are my questions:

1. what components do i need to get this project doing?
2. will this project be cost-effective or not? Meaning whether the components are cheap and readily available.
3. what are the disadvantages of this product? what can I do to improvise?

I have little idea to get this thing going, so I need as much suggestions and ideas from those who are better than me. =)


- eriQue -
i'm still a newbie, SADLY! :p
 
Light travels realy fast!You wod need an extremly acurate times to do so and an super fast way of detetcing light that bounces back.

If you have seen the devices that you point at somting and they tell the distance most have an laser.This is probobly confusing you.The laser is there just so that you cann see the distance of what object you are mesuring.The meshuring is done whith sound.The device makes an ultrasonic beep of about 40kHz (you cant hear that becose the feq. is too high) and then listens for the beeps echo.It also meshures the time taken from the making the beep and the echo to come back.
This time is then multeplyed by the half of the speed of sound and you have the distance.

The easyest way to do this is to use an microcontroler.(An microcontroler or MCU is a whole programable computer in a single chip whith evryting it needs like RAM,the CPU,Porgram and data memory,comunicatin...)

As for the stuff you need:
-PIC microcontroler (dont wory there things are cheap)
-An ultrasonic transdocer
-Op amps

The PIC microcontrolers from Microchip run up to 20Mhz.All it needs to do is first output an 40 Khz signal on one I/O pin and count the ms until it gets an pulse from the reciver that the echo has arived.Then it makes a litle math and displays it on an LED or LCD display.Then is repets this proces and keeps doing it until you shut it off.

It not all the complicated as it seems
 
Someone Electro said:
Light travels realy fast!You wod need an extremly acurate times to do so and an super fast way of detetcing light that bounces back.

If you have seen the devices that you point at somting and they tell the distance most have an laser.This is probobly confusing you.The laser is there just so that you cann see the distance of what object you are mesuring.The meshuring is done whith sound.The device makes an ultrasonic beep of about 40kHz (you cant hear that becose the feq. is too high) and then listens for the beeps echo.It also meshures the time taken from the making the beep and the echo to come back.
This time is then multeplyed by the half of the speed of sound and you have the distance.

The easyest way to do this is to use an microcontroler.(An microcontroler or MCU is a whole programable computer in a single chip whith evryting it needs like RAM,the CPU,Porgram and data memory,comunicatin...)

As for the stuff you need:
-PIC microcontroler (dont wory there things are cheap)
-An ultrasonic transdocer
-Op amps

The PIC microcontrolers from Microchip run up to 20Mhz.All it needs to do is first output an 40 Khz signal on one I/O pin and count the ms until it gets an pulse from the reciver that the echo has arived.Then it makes a litle math and displays it on an LED or LCD display.Then is repets this proces and keeps doing it until you shut it off.

It not all the complicated as it seems
Lasers are used for rangefinding. Just do a Google search. In fact, in the advertising banner at the top of this thread, there is (was?) an ad for one made by Hilti with 2" to 660' range, 1/16" accuracy, for $349 US.
The speed of sound in air is a function of temperature and atmospheric pressure, etc. Also, wind will cause an error. The velocity of light is pretty much constant in air (humidity has a tiny effect).
 
I know they use lasers for this too,but if he wants to make his own rangefinder ultrasonic wod be much easyer to do.

In his case he probobly dosent need as much acuracy.cheap comercial rangefinder use ultrasoic too.
 
Thanks !

The idea on the ultrasonic is great, but in the real world, there would be much interference or noises that could affect the measurement. Am I not right? Laser will do the job a lot better and at a higher accuracy level. So, i'm still left pondering how I'm going to start off this project. I believe that one need the laser diode (HeNe) and the basic device requires some mirrors for calculating angles and the distance. If possible, i'd like my project to measure the distance without the aid of these mirrors or splitters. After calculating the distance, i'd like the device to display the numbers on a 7-segment (which is no big deal). again, how much would this project costs overall? Oh yeah, since it's a laser range finder project... it's gotta be laser equipped. 8)
 
The noise has to be exsactly 40kHz to interfear it.These ultrasonic recivers act as a microphone but it can only hear 40Khz evryting else is filterd out.

So someone driling a hole it shont mess whith it.

The profesional eqipment makes an laser pulse and then meshures for how long it takes for the laser to bounce back.

btw: HeNe is used in a high power high voltage lasers.(They need up to 30 000V to start up and up to 5 000 V to run)

An diode laser is simple an LED that has an lens to focus the beam in to a starit line.This is useb by laser pointers since it only needs a few volts to run.
 
if i use a normal laser pointer, then how does the laser gets bounced back to its source? in that case, it will probably need some mirror to reflect the lasers? i want to eliminate this. there are equipments that doesnt need the aid of the mirrors. how am i going to go about to build this circuit??? :roll:
 
erique82 said:
if i use a normal laser pointer, then how does the laser gets bounced back to its source? in that case, it will probably need some mirror to reflect the lasers? i want to eliminate this. there are equipments that doesnt need the aid of the mirrors. how am i going to go about to build this circuit??? :roll:
I would think that if you can see the reflection off your target, then you should be able to build a sensor that can "see" it.
 
The target dosent have to be an miror.It just works the best if the object reflects light.

If you wod reflect the laser directly in to the sensor whith a miror you cod get huge meshuring ranges.

Did you take in acout that light travels slitly less then 300 000 000 m/s.So if you have an 1 us (1/1 000 000 of a second) acurate clock you wod have 150 m acuracy! If you have an 1 ns (1/1 000 000 000 of a second) you wod have 15 cm acuracy.

An easy PIC microcontroler is out of the question in this case since it needs 200 us to complete 1 instrucion.

Sound goes about 330 m/s so whith realy poor timing acuracy of 1 s you get 165 m acuracy.So you need about one milion times beter clock for laser range finding.

How acurate do you need it any way?(is it worth going trough the truble of makeing an super fast clock?)
 
Nigel Goodwin said:
Ron H said:
**broken link removed** is a great reference on laser rangefinding techniques.

The first page certainly looks impressive!, incomprehensible, but impressive :lol:

I imagine it's EXACTLY what erique82 is looking for!.
Nigel, I won't blame you if you are being sarcastic. I gotta confess that the first page looks somewhat daunting. I actually started out somewhere in the middle, having arrived via a Google search. I'm not sure I would have gotten past the title, otherwise. There is some good info inside. There might even be something about a simple rangefinder. :)
Whether it is comprehensible by erique82 depends on how smart he is. :roll:
 
I would modulate the laser beam with a variable frequency sine wave, and sweep the freq. while it's pointed at the target. Both signals (transmitted and reflected / received) could be passed into a mixer. Then, at any frequency where the mixer output has a zero DC value, you know the signals are in-phase, and the target is a certain number of half-wavelengths away (the brightness of the beam looks like a sine over time and space, just like field intensities in an RF wave)--the lowest frequency at which the phases are equal will correspond to a wavelength of twice your distance. The AC output of the mixer can also be used, to indicate the target's velocity.

The frequencies involved will only have to go high enough to measure the shortest distance the unit has to be capable of. Frequencies in the hundreds of MHz would give a min. distance of a few meters, where 2-3GHz would let the distance go down to maybe a few inches.

If you just want to see the thing work, you can replace about 90% of the electronics (all the hard stuff, basically) with a Vector Network Analyzer. Use one port to AM modulate the tx, and feed the AM-detected signal from the rx into another port. The VNA can then display the phase shift between the two signals (look for the first zero).
 
Ron H said:
Nigel, I won't blame you if you are being sarcastic.

Not at all, it was a genuine comment!.

I gotta confess that the first page looks somewhat daunting. I actually started out somewhere in the middle, having arrived via a Google search. I'm not sure I would have gotten past the title, otherwise. There is some good info inside. There might even be something about a simple rangefinder. :)

I don't think 'simple' and 'laser rangefinder' are likely to find themselves in the same sentence very often!. But the article should be all he needs, after all presumably it's a University course he's on?.
 
thank you!

thank you all for your help. i really appreciate it. the article was a major help, it gave me some ideas on my project. well, if i encounter any problems in the future, i know where to get help. 8)
 
A) acctualy the ulrtasonic emmiter/ receiver pair are extreamly well tuned and pick up very little interference. surely a the detection of the lazer wil be affected by the natural and artificial light of your suroundings?

i was going to say:
B) you need very high clock speeds to do the old timing trick with lazers, although the half wave idea sounds interesting. however unless the lazer comes back on exactly the same route it was emmited from you wont notic any supperposition, the two lazer paths (emmited and reflected) would need to be on top of each other. or do you plan to place the lazer detector in the same place as the emmiter.

but then i re-read your method and realised what ur doing :oops: . that a very interesting method. please keep me updated on the results of that


all sounds very complicaded. i'll leave you with this comment, for short distance ultrasonics are far more convenient
 
Yea these ultrasonic trancevers are only sensistive to stricly 40khz (Some may work at difrent feq.)So if there are peole yeling in that room it will not pick it up.
 
8) this is a lot harder than i thought

well, there are a few techniques that a person can use to build a laser rangefinder. There are 4, if i'm not mistaken ...

1. time of flight (TOF)
2. triangulation
3. interferometry
4. phase shift

which one of these techniques should i use? My scope is around 0-50 metres. I heard that TOf offers the best accuracy, but it's hard and time consuming to build. Not to mention complex. I only have about 5 months to finish this project.



-erique
i just want to build a darn prototype



8)
 
I finally decided on building my laser rangefinder based on phase shift method. I've read about the Time-of-flight (TOF) method, and i think that method is rather too complex. I'm wondering if I could use a normal MC68HC11 as the microcontroller for this project... and oh yeah, is an 8-bit ADC sufficient? Or do i need a 12-bit instead? There should be some optics required, and i wonder if any normal telescopic lens is ok? help me help me :roll:
 
Someone Electro said:
Did you take in acout that light travels slitly less then 300 000 000 m/s.So if you have an 1 us (1/1 000 000 of a second) acurate clock you wod have 150 m acuracy! If you have an 1 ns (1/1 000 000 000 of a second) you wod have 15 cm acuracy.

Latest dsPICs are 25nS instructions, 6.25nS clock.

However noise discrimination is a mind-boggling problem. I mean, a 5mW laser pointer for example is not really visible to the human eye in daylight at even a foot. So a receiver is going to see a signal-to-noise ratio with thousands or millions of times more noise.

You would pulse the signal as a known freq and look for that freq in the light, but it's still a daunting problem to pick up that reflected signal. Moreover, if you're going to digitize the signal and do digital filtering, the ADC is far far slower than the chip. 100kS/sec is a fast ADC. Detecting phase shift of a lower amplitude than the sample rate, not sure how practical that's going to be.
 
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