simple laser distance measurement/laser range finder

want to build a "laser range finder"* to measure a distance of approx 70 meters...
help required for components and any schematics to build one..,i am trying using the 650nm CW laser diode with a collimator and receiver is a PIN/APD diode...can anyone suggest how to proceed with above few components or any new one to workon will be much helpfull...
optics for receiver section,i am planning to use a plano-convex lens,but not sure...suggesstion needed...

thank you...

*there are few old similar threads but i had a problem linking them here,plz consider...

70 meters means round trip is 140 meters. Light will travel the distance in 470 billionths of a second.

Your range finder needs a timer circuit which operates fast enough to measure that small span of time. Maybe a 1 GHz clock rate would do it, if you are content with accuracy to a few percent.

You'll need some kind of telescopic sight, to capture the reflected beam and focus a sufficiently bright beam on the photodiode.

Off a diffuse target I think you will struggle with a CW, eye safe, visible laser at 70m although it is not impossible. After hitting your distant target the light will be scattered in all directions so the amount of light you will receive at you photodiode will be very small. I think an APD will be necessary. Have a look for an AVR project based on the principles of a Bosch laser tape measure - it should give you some ideas. I don't have the links available at the moment.

Keith

BradtheRad said:

70 meters means round trip is 140 meters. Light will travel the distance in 470 billionths of a second.

Your range finder needs a timer circuit which operates fast enough to measure that small span of time. Maybe a 1 GHz clock rate would do it, if you are content with accuracy to a few percent.

You'll need some kind of telescopic sight, to capture the reflected beam and focus a sufficiently bright beam on the photodiode.

Click to expand...

thank you for your early reply, yes i agree... but how about using a plano convex lens,with a band pass filter... may be they are a bit costly...im really confused in selecting the components..:-?, i will surely try, any schematics about the receiver section will help me...

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keith1200rs said:

Off a diffuse target I think you will struggle with a CW, eye safe, visible laser at 70m although it is not impossible. After hitting your distant target the light will be scattered in all directions so the amount of light you will receive at you photodiode will be very small. I think an APD will be necessary. Have a look for an Arduino project based on the principles of a Bosch laser tape measure - it should give you some ideas. I don't have the links available at the moment.

Keith

Click to expand...

thank you keith, what about using a pulse wave laser, i think pulse wave laser as higher wavelength and it goes to infrared or near infrared,then the light can not be seen, that is what im thinking about... and APD is the best choice but at 70 m distance the light is scattered and i have a problem in finding the correct optic lens to focus on APD...any suggestions...

I doubt a plano-convex is going to be good enough to give you a good spot shape/size unless it was long focal length and small diameter. Similarly for focusing the received light onto the APD. Look for an asphere - there are quite a few low cost aspheres around that will do a lot better job. I have used some from Edmund Optics and they are very good.

Keith

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Just to add - a 905nm (or similar) will be far easier at that distance but it depends on the accuracy you want an also minimum distance.

bogalark said:

with a band pass filter

Click to expand...

You will send a laser burst, then start a loop where you (a) increment a timer variable, (b) examine the photodiode level for a sudden change in brightness.

It needs to be an abrupt change. Any filtering action could soften the incoming pulse, or create a delay in detection, which will throw off your result.

The OP is talking about optical filters.

FvM said:

The OP is talking about optical filters.

Click to expand...

hi, its my assumption that when the light gets scattered at that distance (70 mts), hope band pass filter will only allow the light of required wavelength to be detected... that is why i said about a band pass filter... any schematics for the pulse laser diode driver?

You are likely to need an optical bandpass filter if you are using an APD due to the high sensitivity which could saturate your amplifier with ambient light and also the excess noise caused by ambient light in APDs.

For laser diode drive circuits, have a look at the Osram application notes on their web site.

Keith

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There is a complete project on AVRfreaks here: http://www.avrfreaks.net/index.php?module=Freaks%20Academy&func=viewItem&item_id=2907&item_type=project
http://www.avrfreaks.net/index.php?module=Freaks%20Academy&func=viewItem&item_id=3061&item_type=project

but you need to register to see it. It uses the multiple phase shift method.

Keith

hi
if not complete schematics of individual components can i get the readily available modules so that i can integrate them to get a laser range finder like 1).laser diode transmitter which includes the laser diode(CW or PW) including the collimator and the laser diode driver
2).laser receiver which includes receiver lens,photo diode and conversion unit(i am not sure, i mean light signal to voltage(electrical signal)).
3).time descriminator/ time to digital converter for measuring the time between start pulse and received pulse(any microcontroller/chip).

if yes, for measuring a distance of 70 mts, can anyone specify the specifications that are appropriate to make a module..

thanks in advance...

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hi
what about using a 904nm-30mW - Infrared Laser Diodes with the driver(may be complete module) and a 38kHz Infrared (IR) Receiver Module...
:!:

The 38 kHz receiver question clarifies, that you need to get an elementary understanding of laser range finder operation principles as a first step. Please consider that keith already suggested two alternative design concepts pulse time of flight and CW modulation phase shift. Try to understand what are the essentials of both methods and why one or the other might be preferably.

You didn't yet tell about the project motivation and specifications, except for the 70 m range point.

Staying thus quite generally, I would mention two points:
- designing a laser range finder is a challenging project, even a "simple" one
- these days range finders with suitable specification are availabe as mass products. Making your own sounds less reasonable than ever.