With that regardless if the the square is in phase or out, there would be an offset of phase that we can measure. mirrored cicuits, one for the pulse leaving and on for the return. we should get two 50 khz square wave. If we tune this down a little and send out 10khz pulses (which we can specify from the LDM) we can extend the range to a theoretical range of 18.59 miles/2 or about 9.25 miles.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
i´m contacting you not yet because a purchase of my own but becouse i need urgent help.
i´ve been trying to built a laser range findder but i really don´t know very much about the subject.
i'm working one a final year project of advanced electronics
and i saw your web page with a project of a laser transmitter . so if you please coul send me the information that you have i will be eternally gratefull pricipally if you have any schems and mounting metods..
i wil leave to you the components that i'm using so that could be a guidance to your help.
laser diode splpl90 905nm
laser receiver 905 nm
TDC-GP1
beam spliters (don´t know how to mount them)
ir filter
the laser has to measure between 30 to 100 metters and to be eye safe.
much thanks for your attention and will wait for you reesponse
Whilst I was pondering on a TDM for cable faults I realized that I didn't have to invoke a infinitely short pulse, for fear of the outgoing interfering with the incoming, but a (sharp) half step from on to off would do ( but a low to high would provide a uni-polar bias). The fact that the optical version has separate Tx and Rx sensors would help though.
I would have thought that any low(ish) modulation frequencies would be far longer than the flight time, unless the target was the Moon etc.
Penakova,
Welcome to the forum. All kinds of Propeller processor questions are welcome. BUT if you are looking for ready made solutions to your final year homework you might find you have come to the wrong place.
By the way, I just found out that 5mw is the limit for lmaser pointer imports to the US and some other countries. I suspect that using more power for longer ran ges might get you into trouble in some places.
The trick is to use a single pulse at a very short duration like 20nanoseconds but a very high power like 75Watts. While This seems like a lot of power since it is only on for 20ns the actual energy expelled is eye safe. 75Watts times 20ns is still only 1.5 micro-joules of energy. Very easily eye-safe.
Quite so. Now how would one pulse a cheap laser pointer for such short durations? It may be possible to get some of those dangerous laser pointers here. I might guess it's not so simple to drive them like that.
I recall reading an advert for a 1.5J pulse laser on the back cover of Wireless World. It was one of those ex-equipment houses and they had it for ages.
They stated that it could burn a hole through a steel ruler so it generater dark thoughts, in me, about having a go at the neighbour's car, he kept on parking it across our gates.
Ahhh...Wireless World. Between my father and I we had every issue from the mid 60's to the mid 80's. Essential reading as a teen. Later one old girl friend convinced me to get rid of them in a fit of house tidying. Soon I did not have her or the WW collection. Guess which one I miss the most now?
38KHz sounds low, as that pushes the headaches into the Analog domain, where zero-crossing and phase detect needs to be done to a high precision.
SInce you have not said this is moving, I'll assume it is not, and then you have time on your side, to integrate the minute received energy.
A tuned circuit is one of the best ways to recover energy, AND limit unwanted noise, so it's best to look around for moderate Q tuned elements.
Ceramic resonators in the 200KHz-600Khz region are cheap,and can be augmented with a lower Q LC to further remove suprious results.
At 200Khz one 80MHz LSB is one part in 400, which is more managable, and one full cycle is ~ 1500m. (from above)
If you go over that, I think a technique used is to frequency shift, and then the observed phase movement (dT) is a multiple of the whole cycles.
- so you would send 199KHz and 201 KHz, (or whatever still fits in the pass band)
The speed of light is 299,792,458 meters per second... so taking the inverse, that's about 3.33ns per meter.
Running at 80MHz, the resolution of the Propeller is 12.5ns which would give you a distance resolution of roughly 1.88 meters.
The value of 1.88 meters is half of what you would expect from dividing 12.5ns by 3.33ns, because you apply the "round trip" distance in this circumstance.
"Two childrens (for now) reflecting telescopes.· One for transmit and one for recieve...."
I like this idea, but why not use a laser (transmit) and only one reflecting telescope (receive)?
"Now...· How do we amplify our received laser energy?"
There are several ways this could be done... most commonly you would modulate the laser (transmitter) at a specific frequency or carrier.
On the receiver look for the presence or non-presence of that carrier frequency... apply the same principles that you would for radio when detecting a "carrier", but apply them to the laser beam instead. ·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Have anyone considered interferometry? Used this principle in aligning laser paths in High res medical imaging printers but it seems to be useful for distance measurements as well as alignment work.
Have anyone considered interferometry? Used this principle in aligning laser paths in High res medical imaging printers but it seems to be useful for distance measurements as well as alignment work.
I think the problem with using interferometry over long distances is that the coherence of the laser gets lost in the air. From the source you linked to:
Interferometric measurement of distance can be highly accurate. It offers a higher degree of precision than the pulsed time-of-flight or beam-modulation telemetry methods. However, it is best suited to measurements made in a controlled atmosphere (for example, indoors) over distances no greater than a few tens of meters.
Comments
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
i´m contacting you not yet because a purchase of my own but becouse i need urgent help.
i´ve been trying to built a laser range findder but i really don´t know very much about the subject.
i'm working one a final year project of advanced electronics
and i saw your web page with a project of a laser transmitter . so if you please coul send me the information that you have i will be eternally gratefull pricipally if you have any schems and mounting metods..
i wil leave to you the components that i'm using so that could be a guidance to your help.
laser diode splpl90 905nm
laser receiver 905 nm
TDC-GP1
beam spliters (don´t know how to mount them)
ir filter
the laser has to measure between 30 to 100 metters and to be eye safe.
much thanks for your attention and will wait for you reesponse
sincerilly
ishmael garcia
coteshow69@gmail.com
If there were a second detector aimed at the target but not looking at the laser dot, could you subtract this out put and thus subtract the noise?
So did this project end up being able to detect at 9 miles?
I would have thought that any low(ish) modulation frequencies would be far longer than the flight time, unless the target was the Moon etc.
Welcome to the forum. All kinds of Propeller processor questions are welcome. BUT if you are looking for ready made solutions to your final year homework you might find you have come to the wrong place.
By the way, I just found out that 5mw is the limit for lmaser pointer imports to the US and some other countries. I suspect that using more power for longer ran ges might get you into trouble in some places.
They stated that it could burn a hole through a steel ruler so it generater dark thoughts, in me, about having a go at the neighbour's car, he kept on parking it across our gates.
Thank God for garages.
SInce you have not said this is moving, I'll assume it is not, and then you have time on your side, to integrate the minute received energy.
A tuned circuit is one of the best ways to recover energy, AND limit unwanted noise, so it's best to look around for moderate Q tuned elements.
Ceramic resonators in the 200KHz-600Khz region are cheap,and can be augmented with a lower Q LC to further remove suprious results.
At 200Khz one 80MHz LSB is one part in 400, which is more managable, and one full cycle is ~ 1500m. (from above)
If you go over that, I think a technique used is to frequency shift, and then the observed phase movement (dT) is a multiple of the whole cycles.
- so you would send 199KHz and 201 KHz, (or whatever still fits in the pass band)
Have anyone considered interferometry? Used this principle in aligning laser paths in High res medical imaging printers but it seems to be useful for distance measurements as well as alignment work.
Check this link as a start point:
http://utopia.cord.org/cm/leot/Module6/module6.htm
Frank
Hi Frank,
I think the problem with using interferometry over long distances is that the coherence of the laser gets lost in the air. From the source you linked to: