Anyone familiar with maxbotix or similar sonar range finders? Need some wisdom

I was working on a specific rangefinder application, using an entry level Maxbotix MaxSonar EZ 0... then I ran into a brick wall when going from bench top prototype to testing in the field. It's not going to work. Hoping to find a solution.


Here's the application: I'm trying to build a water level logger for a shallow well. The idea is to mount a downward-pointing sonar range finger in the well cover (usually a wooden lid) and generate a timestamped log of distance to the water surface. This is a very useful tool for people who depend on shallow wells (such as myself!). Tells you a lot about usage patterns, replenishment times, etc.

I put together a quick breadboard version with a cheapie SD module, an RTC, 7seg readout, and the MaxSonar EZ0 -- made it 9v battery powered for portability, and went around measuring distances (in inches) to walls, floors, window glass, etc. All seemed to work very nicely. It's an analog gizmo and a little noisy, but sample averaging seems to do the trick.

Then I took it in the bathroom and measured the distance to the surface of a bathtub full of water. That also seemed to work fine, so I thought I was ready to start on the final packaged version. But some nasty sarcastic little voice of experience said I'd better take it to the well house and do one more POC in the actual location.

To my dismay, pointing the sensor down the well casing at the water does not work. I get weird fluctuating readings between 22 and 36 inches, when it's actually about 78 inches to the water surface.

Disappointment and head scratching.

For those who have not had to deal with shallow wells: they are built by stacking concrete rings to the desired depth, in a big messy excavation that is then backfilled around the concrete. Spring or ground water seeps up from the open bottom and fills the cylindrical "tank" thus created, and is drawn off by a pump mounted at the top of the concrete tube. My well casing rings are 48 inches ID. So my sonar rangefinder is sighting down a concrete tube 48 inches in diameter.

It occurs to me suddenly (doh!) that perhaps the beam of this device is wide enough that it's hitting the concrete wall and getting all kinds of echoes that confound the depth reading. Looking at the spec sheet I see that the EZ-0 does indeed have a pretty wide beam.

So my questions for y'all -- especially robotics tinkerers who rely on range finders -- are as follows.

  1. am I intepreting the behaviour correctly? is a wide-beam rangefinder unable to look "through" a corridor or tube of restricted dimension due to echo interference?

  2. are there rangefingers with more focussed/tight/narrow beams? are any of them as narrow as, say, 48 inch spread over 16 feet distance?

  3. any recommendations for specific rangefinder makes and modules?

Yes, in that situation there are all sorts of problems with multiple echos, reflections from irregularities in the side walls, etc.

Ultrasonic sensors are also about the worst choice for a damp environment. Don't expect ANY circuitry to last for more than a month or two, unless it is completely waterproof (quite difficult for a hobbyist).

Explore other options. Floats, bubbler depth sensors, etc. where the electronics are in a dry environment work well.

@jremington thanks, I guess :slight_smile: that was rather a deflating answer, but I suppose better to be forewarned!

I googled the bubbler devices a bit, but can't find any pricing (they are all "call for quote" which suggests to me that the price is high). a float system is mechanically impossible (no headroom at the well head). I could dimly imagine a system with reed switches and a floating magnetic puck, but the reed sw would have to be in a submersed tube -- tricky.

maxbotix does have outdoor rated sonar rangers, I noticed. much more pricey than the entry level unit.

I'll keep thinking (and maybe still take it to prototype, even if damp proofing turns out to be a challenge)...

Believe me, I've been quite amazed at how reliably and rapidly circuit boards degrade in similar situations, and other forum members will probably chime in with similar experiences.

To have any hope at all of your circuit surviving for more than a month or two at 100% humidity, "conformal coating" of the entire circuit board and all components is a must, and more likely the circuitry needs to be completely encased in silicone potting compound.

reed sw would have to be in a submersed tube

This is a popular choice. It works well and it is easy to seal a tube, both air and water tight. The float can be contained in a stiff open tube, with the switch tube running alongside.

You might look up DIY sump pump switches to see what others have done.