I hope you've taken safety issues into consideration with the infrared laser. Since humans have no blink response to invisible radiation, a carelessly-aimed infrared laser could do serious retinal damage — even over long distances — without the victim's immediate awareness.
I wasn't thinking so much about you (although that should have occurred to me, and I'm glad you got the glasses!) as much as the collateral damage to people and other critters your beam might intercept. If someone just happened to be looking your way when the beam was on, they could suffer eye damage.
You said...
Now the fun part and this is where I may be dumb.· I am going to use my trusty Parallax O-scope and attach channel 1 to the + power· on the laser.· Channel 2 on the photodiode.· I will use the propeller to modulate 50khz on the laser.· I should see the 50khz on the direct connect to the laser and I should see the returned laser pulses on the photodiode. I should also see a wave shift on the returned signal.· If I am wrong somebody fix me.
In order to determine anything meaningful, you are going to need to amplify and detect the 50kHz signal coming back...· and because it's all a balancing act when it comes to measuring the phase differences, you will also need the exact same circuitry for BOTH channels, even though one channel is directly connected.· The reason is because the detection circuitry introduces some delay of it's own, and you want the same delay introduced to both channels. · I'll post a schematic later this evening... ·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
kelvin james, · Yes, exactly... I'm absolutely sure they use two detectors·so that the signals are better balanced and can use·truly identical detector circuits.· ... I'll post a schematic anyway.· It's basically a narrow band 50kHz +/-2.5kHz·filter that takes a 1mV pK-pK 50kHz signal and outputs a 1V pK-pK·signal... you need two identical circuits for this design to work, and the circuits must be stepped and not mirrored.
Edit: The second version will provide a cleaner output and is·easier to construct. ·
·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 7/25/2008 3:45:25 AM GMT
Sniper King, Using your avatar, you can see the difference between Stepped and Mirrored. · The idea is that in Stepped mode, each unit·and components have the same current flow and·direction orientation.· Under a mirrored circumstance the physical orientation of components and direction of current flow, etc. are different.· ·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Ok, looking at your circuit,· I am seeing you feed a 50 KHZ 1mvpp signal in front of the photodiode.· Is this right or are you showing me what my signal strengths are going to be out of the photodiode.· Also a resistor is not labeled on the lower circuit.
i am going to build this tis week or early next week and send some screen shots of the results.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
"Is this right or are you showing me what my signal strengths are going to be out of the photodiode." · The circuit was designed to·be sensitive to a 1mV fluctuation ... the strengths you see can vary depending on how much energy from the laser is left after 3 miles, and focusing·onto the Photo-diode. · "Also a resistor is not labeled on the lower circuit." · The R value just represents the driver circuit for your laser.· ... The "key" signal her is the 1Meg and 330 Ohms resistor forming a voltage divider with the 3.3V to produce about 1mV · Basically the idea here at the resistor divider is that you have the same signal strength here that you would from the received signal.· You might have to measure the Peak-to-Peak voltage of the Photo-Diode detector first, before you match it with the second circuit.·· ... The Key is Matched strength entering the 50KHz filters.
Edit: 1mV is probably unrealistic ... 20mV is more like what you would see over the normal electrical noise floor.· Attached is a scoped signal off of the LC in the receiver using a 23.2kHz signal (LC combo = 1000uH and .047uF)· ... Even though the signal shows up on the scope, the scope could not get a proper lock to determine the correct frequency.· The width of the pulse shows the normal electrical noise floor at about 10mV.
Regardless, the schematic will work, you just need to adjust the voltage divider accordingly, so that it matches or is close to what you are receiving from the Photo Diode.
·· · · ·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 7/24/2008 5:25:10 AM GMT
OK, the guys at Perkin Elmer are cool and very helpful.· They are sending me 2 avalanch photo diodes and 2 pulsed laser diodes for free as samples.· Attached is the datasheet for the laser diodes.·
Beau, this laser looks really powerful.· can you give me a heads up on it.· Also it is a 100ns pulsed laser.· Is that going to be a 10khz frequency for us to measure off of?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
I am totally not used to working in the nanoseond realm as you can see.·
10 mhz leaves us with multiple pulses at the distances we are working with. is this something we can deal with.· I know for your application this is ideal due to the limited ranges you are looking for.
Can we still modulate 10khz on this and use it with a 10mhz carrier there?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
Post Edited (Sniper King) : 7/25/2008 5:06:22 PM GMT
For lasers that powerful, I would want a sure thing and no room for error. In other words find something of less power to experiment with.
Looking at the datasheet, I believe that the 100ns applies to how long the pulse is allowed to be high under maximum output power conditions and does not refer to modulation frequency... a pulse of longer duration than 100ns under maximum power conditions could burn up the laser.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
The laser and photodiode are on the way (I think)· My sales guy at Perkin-ELmer is not the most reliable.·
OK after reading all the docs on the laser and what is going to go in front of it.· I am going to have to settle on the Time of Flight calculations.· However with a·15 nanosecond pulse at over 60 watts, I think that will be the brightest thing in the universe for about·15 nanoseconds.· I don't think any background light is going to be an issue.·
The issue was rise times of the laser.· We have to get max power out of the laser really fast.· Therefore the use of a Laser Diode Driver is essential.· The one chosen has a rise time of 2ns and pulse length of 15ns.· With 3ns per meter we are under 1 meter accuracy.· However the down side to this is we have to supply 195v to the driver module.· Really low current but still a potent amount of energy.· So a step up votage section is in the works too.·
As far as the receiving section.· The 741 op amp schematic by Beux (sounds like a web site!) is going to be our initial receiving amp.· From there I am going to come up with some kind of glue logic measuring system.· At this point I am leaning toward the RC time folding circuit with some temperature calibration fuction controlled by the propeller to offset any temperature errors that are going to show themselves.· I figure charging and draining the capacitor at regular intervals will give us a calibration constant to work with.·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
To put aside any fears,· I have a desert test range to work with that is completely unpopulated.· I have a verticle cliff to measure off of and safety glasses for everybody involved.·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
"I am going to have to settle on the Time of Flight calculations.· However with a·15 nanosecond pulse at over 60 watts, I think that will be the brightest thing in the universe for about·15 nanoseconds.· I don't think any background light is going to be an issue."
"As far as the receiving section.· The 741 op amp schematic by Beux (sounds like a web site!) is going to be our initial receiving amp."
It's important that you modulate the signal within a range that the Op-Amp can properly respond and don't just rely on·the intensity of the reflected light, failing to do so would result in false readings.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
I am having trouble finding data on exactly what "eye safe" really is in regard to actual numbers. The calculated power of the laser we are using at the power, pulse duration and beam size is .0000015 J/cm^2. that seems pretty small but I cant find anything to compare this to.
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Michael King
Application Engineer
R&D
Digital Technology Group
Yes, the 741 circuit that I posted, only has to "see" 50kHz ... A modulated signal at 50KHz will be seen as 50KHz whether it's 1 foot away or 1 mile away. The difference based on time of flight will be at what phase the 50KHz is seen or received at.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Is there an amplifier that could see our extremely short pulse? I know the photodiode can. It amplifies 100 times out of the package but I know we are going to need more tha n this.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
No matter what we have to see these pulses regargless of whether or not we measure phase shift or just time-of-flight. The laser Diode driver can pulse up to 50khz. Phase shift is not out of the question. But we still need to amplify our pulses so we can measure anything.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
"Is there an amplifier that could see our extremely short pulse?" "Is this an alternative to the 741 in this case?" · The problem is not seeing the pulse or the choice of Op-Amp.· Even though you have a very intense pulse, it's a one-time event, and it's extremely hard to separate that from random noise no matter how bright or strong the signal is.· The technique of modulation is analogous to radio and having a carrier frequency...· It would be very hard to transmit radio without a carrier, and be able to re-assemble the data at the other end and separate it from random noise you would also receive. ·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Lets say then if I am sending 50ns pulses 50000 times a second. Is this this something we can work with. A normal comparator, I think, will not work. I know we can resolve the pulses from the noise. I guess we could just measure the time difference between sent and received pulses.
On the other hand.
If we are measuring ambient noise and notice a spike of 50ns that is somewhat above our noise floor wouldn't this be a way of measuring time of flight?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
One can use a lazer for a listening device by bouncing a beam off a window. Audio striking the window modulates the beam [noparse]:)[/noparse] There must be a primary carrier frequency for that application too.
A 50nS pulse is 1/200th or a 0.5% duty cycle of a 50kHz signal. Using a "tuned" coil and capacitor·tank of 100uH and .1uF, there is enough duration·within that 0.5% duty cycle to cause the tank to have a sinusoidal oscillation of 50KHz.· Think of swinging somebody on a swing... each 50nS pulse would be when you push.· The caveat is that since the pulse is so short, the total energy in that pulse is going to be very small as well.· ... The short pulse could be analogous to pushing someone in a swing, only the person pushing would be doing so with a broken hand. ·
·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
I agree. To fill that "tank" with such a small amount of energy would be alot to ask. What about a highspeed flip-flop to create an artificial squarewave?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ ·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
"If we are measuring ambient noise and notice a spike of 50ns that is somewhat above our noise floor wouldn't this be a way of measuring time of flight?"
You might be able to, but at the distances that you are talking about and how much the signal needs to be amplified (remember, noise gets amplified also), that spike might be hard to distinguish among the noise. Using a tank circuit also works like a filter to suppress some of your noise, thus increasing your signal to noise ratio when you do actually have a signal.... without modulation, you don't have any filtering.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Comments
I hope you've taken safety issues into consideration with the infrared laser. Since humans have no blink response to invisible radiation, a carelessly-aimed infrared laser could do serious retinal damage — even over long distances — without the victim's immediate awareness.
-Phil
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'Still some PropSTICK Kit bare PCBs left!
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·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
-Phil
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'Still some PropSTICK Kit bare PCBs left!
·
I'll post a schematic later this evening...
·
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
·
Yes, exactly... I'm absolutely sure they use two detectors·so that the signals are better balanced and can use·truly identical detector circuits.· ... I'll post a schematic anyway.· It's basically a narrow band 50kHz +/-2.5kHz·filter that takes a 1mV pK-pK 50kHz signal and outputs a 1V pK-pK·signal... you need two identical circuits for this design to work, and the circuits must be stepped and not mirrored.
Edit:
The second version will provide a cleaner output and is·easier to construct.
·
·
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 7/25/2008 3:45:25 AM GMT
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·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
Using your avatar, you can see the difference between Stepped and Mirrored.
·
The idea is that in Stepped mode, each unit·and components have the same current flow and·direction orientation.· Under a mirrored circumstance the physical orientation of components and direction of current flow, etc. are different.·
·
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Ok, looking at your circuit,· I am seeing you feed a 50 KHZ 1mvpp signal in front of the photodiode.· Is this right or are you showing me what my signal strengths are going to be out of the photodiode.· Also a resistor is not labeled on the lower circuit.
i am going to build this tis week or early next week and send some screen shots of the results.
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·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
·
The circuit was designed to·be sensitive to a 1mV fluctuation ... the strengths you see can vary depending on how much energy from the laser is left after 3 miles, and focusing·onto the Photo-diode.
·
"Also a resistor is not labeled on the lower circuit."
·
The R value just represents the driver circuit for your laser.· ... The "key" signal her is the 1Meg and 330 Ohms resistor forming a voltage divider with the 3.3V to produce about 1mV
·
Basically the idea here at the resistor divider is that you have the same signal strength here that you would from the received signal.· You might have to measure the Peak-to-Peak voltage of the Photo-Diode detector first, before you match it with the second circuit.·· ... The Key is Matched strength entering the 50KHz filters.
Edit:
1mV is probably unrealistic ... 20mV is more like what you would see over the normal electrical noise floor.· Attached is a scoped signal off of the LC in the receiver using a 23.2kHz signal (LC combo = 1000uH and .047uF)· ... Even though the signal shows up on the scope, the scope could not get a proper lock to determine the correct frequency.· The width of the pulse shows the normal electrical noise floor at about 10mV.
Regardless, the schematic will work, you just need to adjust the voltage divider accordingly, so that it matches or is close to what you are receiving from the Photo Diode.
··
·
·
·
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 7/24/2008 5:25:10 AM GMT
Beau, this laser looks really powerful.· can you give me a heads up on it.· Also it is a 100ns pulsed laser.· Is that going to be a 10khz frequency for us to measure off of?
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·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
"..Beau, this laser looks really powerful.· can you give me a heads up on it..."·
HUH? I think you are better suited with the optics end than I am. Wear safety goggles! (page 4 and 5 of the PDF)
"...Also it is a 100ns pulsed laser.· Is that going to be a 10khz frequency for us to measure off of?..."
100nS is 10MHz
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 7/25/2008 3:25:31 AM GMT
10 mhz leaves us with multiple pulses at the distances we are working with. is this something we can deal with.· I know for your application this is ideal due to the limited ranges you are looking for.
Can we still modulate 10khz on this and use it with a 10mhz carrier there?
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·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
Post Edited (Sniper King) : 7/25/2008 5:06:22 PM GMT
For lasers that powerful, I would want a sure thing and no room for error. In other words find something of less power to experiment with.
Looking at the datasheet, I believe that the 100ns applies to how long the pulse is allowed to be high under maximum output power conditions and does not refer to modulation frequency... a pulse of longer duration than 100ns under maximum power conditions could burn up the laser.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
The laser and photodiode are on the way (I think)· My sales guy at Perkin-ELmer is not the most reliable.·
OK after reading all the docs on the laser and what is going to go in front of it.· I am going to have to settle on the Time of Flight calculations.· However with a·15 nanosecond pulse at over 60 watts, I think that will be the brightest thing in the universe for about·15 nanoseconds.· I don't think any background light is going to be an issue.·
The issue was rise times of the laser.· We have to get max power out of the laser really fast.· Therefore the use of a Laser Diode Driver is essential.· The one chosen has a rise time of 2ns and pulse length of 15ns.· With 3ns per meter we are under 1 meter accuracy.· However the down side to this is we have to supply 195v to the driver module.· Really low current but still a potent amount of energy.· So a step up votage section is in the works too.·
As far as the receiving section.· The 741 op amp schematic by Beux (sounds like a web site!) is going to be our initial receiving amp.· From there I am going to come up with some kind of glue logic measuring system.· At this point I am leaning toward the RC time folding circuit with some temperature calibration fuction controlled by the propeller to offset any temperature errors that are going to show themselves.· I figure charging and draining the capacitor at regular intervals will give us a calibration constant to work with.·
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·- Was it pin 11 or 26?· Hmmm....··I think the smell of smoke tells the whole story.· Must be 26.
Michael King
Application Engineer
R&D
Digital Technology Group
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
I'm not sure this would help, but you might consider a laser line interference filter. They notch the incoming frequencies down to a few nanometers of your laser. See for example NT43-099 on http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=1903
It's center line is at about 905 nm. FWHM is 10nm. It might help cut down on stray IR.
You can get even better filters if you're willing to change your laser wavelength, http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2581.
Hope that helps,
just don't use it to shoot ME,
Mark
PS: oops,sorry, I was responding to an old post concerning this...
"I am going to have to settle on the Time of Flight calculations.· However with a·15 nanosecond pulse at over 60 watts, I think that will be the brightest thing in the universe for about·15 nanoseconds.· I don't think any background light is going to be an issue."
"As far as the receiving section.· The 741 op amp schematic by Beux (sounds like a web site!) is going to be our initial receiving amp."
It's important that you modulate the signal within a range that the Op-Amp can properly respond and don't just rely on·the intensity of the reflected light, failing to do so would result in false readings.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
Yes, the 741 circuit that I posted, only has to "see" 50kHz ... A modulated signal at 50KHz will be seen as 50KHz whether it's 1 foot away or 1 mile away. The difference based on time of flight will be at what phase the 50KHz is seen or received at.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
http://www.analog.com/en/amplifiers-and-comparators/operational-amplifiers-op-amps/ad8000/products/product.html
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
"Is this an alternative to the 741 in this case?"
·
The problem is not seeing the pulse or the choice of Op-Amp.· Even though you have a very intense pulse, it's a one-time event, and it's extremely hard to separate that from random noise no matter how bright or strong the signal is.· The technique of modulation is analogous to radio and having a carrier frequency...· It would be very hard to transmit radio without a carrier, and be able to re-assemble the data at the other end and separate it from random noise you would also receive.
·
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
On the other hand.
If we are measuring ambient noise and notice a spike of 50ns that is somewhat above our noise floor wouldn't this be a way of measuring time of flight?
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
There are MPE charts in·http://en.wikipedia.org/wiki/Laser_safety wiki for various frequencies and strengths for collimated and other lasers.
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--Steve
Using a "tuned" coil and capacitor·tank of 100uH and .1uF, there is enough duration·within that 0.5% duty cycle to cause the tank to have a sinusoidal oscillation of 50KHz.· Think of swinging somebody on a swing... each 50nS pulse would be when you push.·
The caveat is that since the pulse is so short, the total energy in that pulse is going to be very small as well.· ... The short pulse could be analogous to pushing someone in a swing, only the person pushing would be doing so with a broken hand.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
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·- Ouch, thats not suppose to be hot!··
Michael King
Application Engineer
R&D
Digital Technology Group
"If we are measuring ambient noise and notice a spike of 50ns that is somewhat above our noise floor wouldn't this be a way of measuring time of flight?"
You might be able to, but at the distances that you are talking about and how much the signal needs to be amplified (remember, noise gets amplified also), that spike might be hard to distinguish among the noise. Using a tank circuit also works like a filter to suppress some of your noise, thus increasing your signal to noise ratio when you do actually have a signal.... without modulation, you don't have any filtering.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.