Do you know any small size, light weight distance sensor with the following specs; * Range : 10cm to 1000cm (10meter ) * Rate : 50 Hz (50 measurements/sec) * Accuracy : 1cm * Must operate on any surface (except transparent surfaces like glass) * Power requirement : Less than 5W * Weight : Lighter than 500grams * Vibrartion sensitivity : Must operate 0-500Hz
No, but I guess they excist. You could use RADAR, simply send out sound, and see how long time it takes for it to return (knowing sound travels more or less 300m/s. This would make it dependent on the altitude, but it'd be easier to make with a microcontroller than light/radio based RADAR, since light would require really really good timing...
-- MVH, Vidar www.bitsex.net
Interesting criteria
Speed of sound is about 340 meters per second, if you want a range of 10 meters, that is a round trip of 20 meters. 340 meters per second / 20 meters round trip, that means a theoretical maximum of about 17 readings per second, and a practical max of about 10.
Unless you can alter your specifications, SONAR is out of the question and you'll have to use rangning RADAR.
Ranging RADAR is expensive because, unlike police speed traps which use dopler frequency shift on the bounced return signal, a ranging radar system, like a ranging sonar system, needs to measure between send and recieve. Where sound travels at a pokey 240 meters per second and can be easily measered, light travels a little less than 300,000,000 meters per second, and requires some real precision to measure. Especially at the cm to 10 meter range.
Indeed.
Unless, he alters the frequency for each reading. Using different frequencies, and only listening for the right frequency, you might make it work... but then again, Ranging RADAR is better.
-- MVH, Vidar www.bitsex.net
mlw wrote in news: snipped-for-privacy@comcast.com:
Not necissarily -
What about the samll commercial distance measuring units they sell at builders shops? Cheap and easy to get, But I dont know about the specs
David
Use of light or radio pulses (as in RADAR) is just as easy as use of sound pulses; timing is easy. Been around since the 1940's.
So? Radio waves travel about 11 inches per nanosecond (30cm); which is a long time. So 10cm is about 0.3nSec (one way) which means some special care must be taken or subterfuge - like variable CW: make the time of flight a part of an oscillator and then measure the frequency. Makes the job a lot easier, methinks. 1cm accuracy translates to 2cm round trip variance or 60pSec if one thinks of pulses. Lessee...say 2000cm max round trip is 66.67nSec time for 14.999MHz;
1998cm round trip is 66.60nSec time for 15.015MHz. Seems to be easily resolvable. Just build an amplifier and it will oscillate...
Ranging radar is very much more difficult than dopler radar. Dopler radar is fairly easy to do, $100 bucks or so -- hell you can buy dopler radar off the net to measure your pitching speed.
Ranging radar has to emit a pulse and measure the time delay from transmit and recieve. With SONAR, this is dist = (340/2)/T (we divide by two because echo is a two way trip), well in the millisecond range. With RADAR this is dist = (300000000/2)/T. If you are measuing meters you are in the nano second range. If you are trying to measure centimeters you are in the pico second range.
This is not to say it can't be done, but it would be very expensive.
Where ? Any source please?
: > Interesting criteria : : Indeed. : : > Speed of sound is about 340 meters per second, if you want a range of 10 : > meters, that is a round trip of 20 meters. 340 meters per second /
20 : > meters round trip, that means a theoretical maximum of about 17 readings : > per second, and a practical max of about 10. : : Unless, he alters the frequency for each reading. Using different : frequencies, and only listening for the right frequency, you might make : it work... but then again, Ranging RADAR is better. : : : -- : MVH, : Vidar : :
You can't meet the 50Hz requirement at maximum range with sound in air, the best you could get would be about 16Hz. (assuming 330 metres/second)
Deep.
Check into the SICK laser rangers. Not cheap, though.
-- (Replies: cleanse my address of the Mark of the Beast!) Teleoperate a roving mobile robot from the web: http://www.swampgas.com/robotics/rover.html Coauthor with Dennis Clark of "Building Robot Drive Trains". Buy several copies today!
There are ways round this.
If you transmit continuously a signal modulated with a PRBS pattern, then the receiver can find the range at any instant by correlation - basically find the time slip that gives maximum correlation between transmitted and received patterns. This also works for multiple objects in the FOV. Hardware wise this would probably be easiest done with a small fpga.
Laser rangefinders have a similar trick. Basically you modulate the transmitted signal with several different frequencies, and measure the phase difference between Tx and Rx signal for each one. With a judicious choice of frequencies, there is only a single range at which a given set of phase values can occur.
The Tx and Rx sensors need to be physically separated so that the Rx does not get overwhelmed.
Yet another approach feeds back the received signal to the transmitter, so that the whole system oscillates. The frequency of oscillation is directly related to the round trip delay and hence distance.
Have fun ! Dave
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There are ways round this.
If you transmit continuously a signal modulated with a PRBS pattern, then the receiver can find the range at any instant by correlation - basically find the time slip that gives maximum correlation between transmitted and received patterns. This also works for multiple objects in the FOV. Hardware wise this would probably be easiest done with a small fpga.
Laser rangefinders have a similar trick. Basically you modulate the transmitted signal with several different frequencies, and measure the phase difference between Tx and Rx signal for each one. With a judicious choice of frequencies, there is only a single range at which a given set of phase values can occur.
The Tx and Rx sensors need to be physically separated so that the Rx does not get overwhelmed.
Yet another approach feeds back the received signal to the transmitter, so that the whole system oscillates. The frequency of oscillation is directly related to the round trip delay and hence distance.
Have fun ! Dave
Posted Via Nuthinbutnews.Com Premium Usenet Newsgroup Services
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following
Yugo - I don't know if the range or all other constraints are satisfied, but you may want to have a look at the Sharp ranging modules, IR based IIRC. Have a look on the Manuco website. rob
Leica has a few hand-held laser distance devices that seem close to your specs.
Below is some data about their higher end system. But they also have a cheaper version that has the similar measurement abilities. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D The Leica DISTO=99 plus is the only device in the world that offers the highest accuracy, attractive design and wireless data transfer by means of BLUETOOTH=AE in one package. Even if you are currently still working with paper and pencil, integrated BLUETOOTH=AE technology allows you to make the change at any time and to record your values electronically. The data can be transferred on site wireless to a PDA (Pocket PC) or directly to a laptop and easily used for other purposes.
Range of measurement: 0.2 up to 200 m (0.7 up to 650ft). Accuracy: =B11.5mm (0.06in) =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Regarding price; I looked at a similar system by another vendor a few years back and it was around $800 at the time.
Joe Dunfee
No, you can get higher, ... ... why wait until a pulse is received ? Ok next thing to do is "modulate" the pulses, for example, send a puls send a second puls 10 msec later next puls 15 msec later next puls 12 msec later By now combining the results of multiple measurements, you can avoid the ambiguity.
A more diffcult way is to use continuous wave (of course modulated) ultrasound.
Stef Mientki
How do you differentiate between pulses? What about echos from multiple surfaces at different distences?
Try the Sharp GP2D12 sensors.
Steve
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