MaxSonar-EZ1 (a great ultrasonic sensor) is featured in three magazines!

Nuts and Volts, Circuit Cellar, and Sensor Magazine have all featured the MaxSonar-EZ1 <www.maxbotix.com> sensor.
The "Circuit Cellar" write up is found here http://www.circuitcellar.com/library/newproducts/191/maxbotix.htm
and the industrial Magazine "Sensors" write up is found here http://www.sensorsmag.com/sensors/content/contentDetail.jsp?id16342
The Nuts & Volts article is only found in the May print copy.
It all started here on this Usenet group in January. Things are ramping up at MaxBotix and we would like to thank all the guys that were in the original discussion.
There is a lot more info in the FAQ section of the MaxBotix website, so even if you have visited before, you might want to look at this section. For example, the sensor beam angles are posted, code examples, and a link to one user who figured out a very good way to use the sensor outside.
http://www.maxbotix.com/MaxSonar-EZ1__FAQ.php
Again, thanks,
Bob Gross
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I'm always interested in ultrasonics, and I've no doubt this is a good sensor, but I don't believe all that's written in the FAQ ;-) === quote The signal from the transducer is amplified by a bandpass-filter/amplifier, followed by another bandpass filter/log-amplifier, followed by an integrator with integrated gain, followed by an analog to digital converter integrated in a microcontroller. This system yields continuously variable gain from less one to over 1000. The microcontroller continuously performs signal processing techniques to extract the distance. Some users have asked for finer resolution, but the time between readings is used by the software to evaluate the signal. This type of circuit performs much better than simple comparator thresholds, single gain, or switched gain type circuits. === end quote I don't see a log amplifier in the circuit, and can't see how the gain is controlled in a range of less than 1 .. 1000, ... so if the "signal processing techniques", and the rest of the FAQ is equally true ....
cheers, Stef
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Stef,
Thanks for your comments.
This is a completely new design and it may be hard for you to understand. Please enter the schematic into PSpice. (The analog section fits into the student version of Pspice.) You will see a very good log amplifier. This sensor does work as advertised. In addition, some gain is digital and some is analog and so the sensor does function as stated in the FAQ.
Best regards,
Bob Gross www.maxbotix.com
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hi Bob,
Bob (Robot Wars Thumper 1997) wrote:

Sorry I doubt about your claims, at as said, I believe it's a good sensor, but I really like to understand it. And the issue I really like is the 1 sensor approach !
Please enter the schematic into PSpice. (The analog

I looked into the schematic, but I can't find the logarithmic section. Could you point me where it's located ? Is it some non-linear (ff course it must be non-linear ;-) effect which I can't discover ?
Another point I don't understand, if it's so good, why can't you measure with greater resolution than 1 inch ?
cheers, Stef
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Stef, I am not sure what you are asking here. If you put the schematic into PSpice the log amplification will be very apparent. The circuit will fit into the free student version of PSpice. Here you can see for yourself the operation and how it works.
Have you tried the sensor? The precision is what most people describe as incredible especially if they have used the competitor's sensors where readings are expected to jump around. The MaxSonar-EZ1 sensor will output the same number until the object you are sensing moves closer or farther from the front sensor face. This is a big deal, to get real repeatable data, at full speed and not having to deal with sensor non repeatability. In addition, the beam width is controlled by the variable gain, so this yields a very controlled narrow beam while, still maintaining the very close and long range operation.
People have really liked this sensor. I have had virtually no complaints about the operation, but many many kudos! Many people have especially liked the very small size (the PCB is smaller than "the worlds smallest"), and the user interface, the narrow beam, the low power...
http://www.maxbotix.com/MaxSonar-EZ1___Others_Say_.php
www.maxbotix.com
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Bob (Robot Wars Thumper 1997) wrote:

hi Bob, I've to make my excuses,... ... I studied the schematics again,... ... and I overlooked the diodes in the feedback loop,... ... so indeed it's a real logaritmic amplifier.
Ever thought of increasing the accuracy ? By accident I just read an article, which claims 0.05 mm accuracy. They use FSK and use a simple 1 bit correlator. I'm hoping to try this in the next couple of weeks, using normal correlation of the measured zero crossings. I'll keep you informed, might be an idea for your next version (I'm just an interested hobbyist, no intentions at all to sell anything ;-)
cheers, Stef Mientki
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Awesome -- good to hear it, so are you looking at turning a profit (get out of the $ hole) sooner than you were expecting? I think I remember you were (from your estimates) looking at it taking at least a year if all went well..
meanwhile I was using your sensors on a ground vehicle project (i made a pic based multiplexer for the sonar: reconnsworld.com/serial_mux.html) but then I graduated and the ground vehicle project (this year's team) fell apart. oh well, it happens
-andrew reconnsworld.com
Bob (Robot Wars Thumper 1997) wrote:

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I really do *love* this sensor, except for one major problem and one minor gripe:
Problem: at power-up the sensors should be at least 14 inches (I may have this value slightly wrong, but it's in the neiborhood) from any solid object. This is difficult for me to guarentee.
Gripe: I *hate* the inverse TTL-level serial. This is only minor because I can use both pulse-width and analog voltage to read the sensor.
And I also hope that you turn a profit as quickly as possible.
Andrew wrote:

--
D. Jay Newman ! Author of:
snipped-for-privacy@sprucegrove.com ! _Linux Robotics: Programming Smarter Robots_
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I appreciate your comments.
The problem (having to keep objects away from the front face during power up) you discuss was done to solve another problem, this, being able to detect within the so called "dead zone". Other single sensors do not provide the ability to detect to the front face at all. This is not really a problem if you don't want to detect closer than 6 inches, yet if you do, you can.
The serial output has been used by many individuals to evaluate this sensor. The ones with "stamp" type micro-controllers and in the home automation area have really liked the serial output from the sensor. It has also really helped MaxSonar-EZ1 sales to OEMs and distributors as they are able to easily evaluate the sensor by directly connecting directly to a PC and using hyper terminal. I also feel that teachers will be able to demonstrate the sensor to students if they would like. Hyper terminal allows a very large font so one is able to see the range at a distance. Sorry that you would like the other polarity. I hope to accommodate your serial request sometime in the future. Right now we are growing very fast and this growth is the area we have focused.
Regards,
Bob Gross CEO MaxBotix Inc. www.maxbotix.com
D. Jay Newman wrote:

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Bob (Robot Wars Thumper 1997) wrote:

For people on this list who are not familiar with sonar modules, there are two broad classifications -- single sensor and double sensor. A single sensor module has a single ultrasonic transducer that acts as both a transmitter and a receiver. The old Polarioid sensors and the MaxSonarEZ-1 are examples of the single sensor modules. A double sensor double sensor module has a dedicated transmitter module and a dedicated receiver module. Example double sensor modules are the SRF04 and the Ping. The single sensor modules have issues associated with measuring objects up close, since they can not transmit and receive at the same time. The double sensor modules do not have this particular issue. The double sensor modules tend to be larger since they have two transducers.

I, too, think the other polarity is preferable, but it is ultimately your design choice.
Even if you reversed the polarity on the MaxSonar-EZ1, I personally would not use the serial output, since it only resolves distances to whole integer units of inches, no fractions. So for the increased resolution I desire, it is necessary to use either the analog or pulse width interface on the MaxSonar-EZ1.
--

Over the past several years the amateur roboticist has gone
from a lousy selection of ultrasonic sensors (basically just
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Yoy mention "The single sensor modules have issues associated with measuring objects up close, since they can not transmit and receive at the same time. The double sensor modules do not have this particular issue."
Measuring objects up close with dual sensor models The dual sensor models, as one gets closer and closer to the front surface, are forced to have a blind spot and dead zone because the sent signal is not lined up with the receiver so refection does not make it back so they also have a "dead zone". The dual sensor models become completely blind when an object is too close (and yes this can be as close as 1cm to 3 cm), but when this happens the sensor is blind.
Measuring objects up close with single sensor models While it is true that single sensor modules cannot transmit and receive at the same time, they really do not have to. They first transmit, and then receive. But there is the problem with ringdown (where you have just deposited a great deal of energy on the sensor, and where you must also be able to detect on top of that ringdown, a small return signal) and how to deal with that. What I found was that the ringdown pattern is not consistent, day to day. So although the MaxSonar-EZ1 can measure within the presence of the ringdown pattern, the ringdown, is not consistent. So the MaxSonar-EZ1 sensor records this pattern and then detects changes to this pattern. This way the MaxSonar-EZ1 can detect all the way up to the front sensor face, even objects pressing against the front face are detected. This comes with the price of needing to know what the normal ringdown pattern is, hence the required calibration.
Bob Gross CEO MaxBotix Inc.
Wayne C. Gramlich wrote:

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Bob (Robot Wars Thumper 1997) wrote:

That's a nice theory, but in practice the two dual sensor modules I am familiar with (the SRF04 and the Ping) can sense objects all the way to down to 0. I've never had one give me an infinity reading when an object was on top of it. Does anybody else want to chime in with their SRF04 and/or Ping experience?

Whatever you do, it works.
However, as Jay mentions, it is not always possible to ensure that there is a blank space in front of the sensor on power up (e.g. the robot parked next to a wall with the sensor pointed at the wall.)
-Wayne
[snip]
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The MaxSonar-EZ1 sensor may not exist today if my daughters robot was not stuck on a wall, the SRF04 was blind, becasue it was too close. My initial experiments showed that this particular sensor would not detect closer than about 1 cm. I am going to repeat these tests and eventually publish, but you will find that when you use the SRF04 sensor, it will stop detecting when you get too close. If pressed against the wall (or your hand) the signal exiting the sender cannot make it to the receiver. Just physics.
Two cents...
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Bob (Robot Wars Thumper 1997) wrote:

My experience differs from yours. I have never received an infinity reading when an SRF04 is against the wall. Likewise from a Ping.
With regards to physics, your average wall is not neither a perfect ultrasonic energy absorber nor reflector. Some energy gets absorbed and rereadiated. This is why you can hear people on the other sides of walls. Basic physics.
-Wayne
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Again, these sensors even state in their own web sites, 1 to 3 cm for the SRF04, and about cm for the Ping. I have measured both of these sensors, many times, during my comparison tests. I have both sensor types, as well as the larger 2" round ones, but I guess you have different experiences.
Bob Gross CEO MaxBotix Inc.
Wayne C. Gramlich wrote:

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Bob (Robot Wars Thumper 1997) wrote:

The spec. sheets for both the SRF04 and the Ping specify the range at which they can take accurate measurements. They do not specify the behavior when out of range.
While the SRF04 spec. sheet does not specify its out of range behavior at less than 3 cm, here is what Gerry Coe (the person who designed the SRF04) says in the SRF04 technical documentation at the following web URL:
<http://www.robot-electronics.co.uk/htm/srf04tech.htm
To quote:
It [the SRF04] will reliably measure down to 3cm and will continue detecting down to 1cm or less but after 2-3cm the pulse width doesnt get any smaller.
The SRF04 still detects at less then 3cm, it just reports the distance as about 3cm. My experience is that the SRF04 goes all the way to the face plate. Ditto for the Ping.
In other words, the SRF04 behaves pretty much like the MaxSonarEZ-1 only its is last accurate measurement distance is 3cm vs. 6 inches for the EZ1.
-Wayne
[snip]
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Bob (Robot Wars Thumper 1997) wrote:

That's another reason to put a small piece of special formed material between both the transducers, like here http://oase.uci.kun.nl/~mientki/data_www/pic/projects/rapid_prototyping/rapid_prototyping_us_ranger.html
another 2 cents ;-)
cheers, Stef
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Bob (Robot Wars Thumper 1997) wrote:

That's also an algorithm problem. You need to write code to detect stuckness and exploratory (blind) algorithms to get unstuck.
What I want to know is when is someone going to commercialise my 3-sensor sonar? With a transmitter in the centre and two receivers 5cm each side, I can resolve the angular position of the echo to better than 3 degrees with ease. So when your robot is trundling along and sees the leg of a chair, it knows that it's off to the left a bit and can steer around it to the right. It's really *very* effective.
Clifford Heath.
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Clifford,
Get in touch with me, lets talk.
Best Regards, Gerry. http://www.robot-electronics.co.uk
------

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Clifford Heath wrote:

At what distance ?
Anyway I like the idea of 3 sensors.
So when we put all the ideas proposed in this thread together, we get the following specs:
- Multi object detection - Detection range: 0 mm .. 5000 mm - Measurement accuracy: 0.05 mm - Angle detection -40 .. +40 degrees - Angle accuracy: 0.01 degrees - Output serial 19.2 / 115.2 kB - Interrupt output, when object within a given range - maybe it can even give some idea of the size of the obstacle - temperature output 0 .. 50 Celcius, - temperature accuracy 0.5 Celcius - humidity output 20% .. 90% - humidity accuracy 5%
So who is the first one to bring this on to the market ;-)
(I hope to test the high distance accuracy in the next couple of weeks, pure for hobby ;-)
Stef Mientki
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