New Sonar Range Sensor

Bob,
Congratulations on a very classy bit of engineering. I intend to buy one this weekend.
I am curious about the self-calibration you describe in your
data sheet. It looks like at start up the sensor estimates the sound speed for the current conditions and then applies it to subsequent measurements. To do so, it needs to have a sound-reflecting target, but doesn't need to know the actual range to that target. Is that correct? If so, how is the measurement accomplished?
Gary
P.S. To everyone else... At one atmosphere, 20 degrees C (68 F) and 20 percent relative humidity, the sound speed is about 343.6 m/s. At 26.6 degrees (80 F) and 90 percent humidity it's about 348.9 m/s. This might be enough to give a one-inch difference in reading at about six feet. It appears that Bob is the kind of guy who worries about things like that and has engineered a solution. I was wondering how he did it.
Bob (Robot Wars Thumper 1997) wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gary,
I do not want to mislead you on the way the sensor works. The sensor has continuous variable gain (100s of small gain steps) using a log amplifier. Because of the amplifier, the MaxSonar-EZ1 can control the beam width to what is shown on the datasheet.
In addition, the ring down pattern of the sensor is also measured and stored. Then when an object is up close it has a ring down pattern to compare the reading to. The truth is that The MaxSonar-EZ1 is measuring mV of signal on top of volts of signal. This is so the single sensor can detect all the way down to zero distance. This is very reliable.
But the sensor's dynamic loading can change depending upon the air temperature and this change can be mistaken for an up close object. I have had them running for weeks without requiring a repeat calibration, but when I cooled down the MaxSonar-EZ1 (moved near a large ice block in my office) or heated it up (with a small heater) the calibration changed. The humidity affects the exposed sensor and can change the ring down pattern as can the applied voltage. So the calibration cycle is to detect close objects.
At this time the readings are not range compensated for temperature. Maybe this can occur on the next model.
The 0 to 5 V RS232 is mainly for connecting to micro controllers so they don't require a level shifting chip. This is very reliable. I have used the sensor to talk to a PC and for me this has always worked, but no guarantees.
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi Bob,
On Sat, 07 Jan 2006 21:32:39 -0800, Bob (Robot Wars Thumper 1997) wrote:

Need to be careful about hooking up TTL level RS232 to the real deal. Actual RS232 signaling typically ranges +/- 12 volts. The high and low voltages can damage the logic level pins if fed directly into the chip. You wouldn't connect a 9V battery to directly to your PIC without a regulator - similary, don't connect directly to level shifted RS232.
BTW, my shiny new Maxbotix MaxSonar-EZ1's arrived today. Fast shipping, great packaging! Thank you.
-Brian
--
Brian Dean
ATmega128 based MAVRIC controllers
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
When I connect to the PC I have a 1K resistor in series with the (PIC/MaxSonar-EZ1) TX output. From the PC, then I use a 10K in series to the RX input. This prevents any surprises & smoke. Again, maybe not recommended, but I have used it for years for debuging.

greatly appreciated.
Bob Gross
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
what is beam width?
Rich
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bob (Robot Wars Thumper 1997) wrote:

My questions have been answered, and I think you have a good product for the money.
I just placed an order, and will be using it as soon as possible. -- D. Jay Newman http://enerd.ws/robots /
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
D. Jay Newman wrote:

I just got it. Now all I need is to have the time to put it on a robot. Not to mention a bit of example code.
Can you use multiple units together? -- D. Jay Newman http://enerd.ws/robots /
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Posted two code examples. Scroll to the bottom. http://maxbotix.com/MaxSonar-EZ1__FAQ.php Code example for BX-24 and for the BasicAtom. (Code the BasicAtom and Basic Stamp very similar, but not exact.)
The BasicAtom code reads the sensor very fast, and would work well for reading more than one sensor in a row. Sorry, takes two pins per sensor.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.