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My wireless water-level sensor is working fine, and when deployed in the sump-well, it is giving me periodic readings quite well. At this stage, I have the circuit still on a breadboard, and now plan to put it on a veroboard, and finally install this thing in the sump-well for long-term reading purposes.

There are few challenges I am facing and few that I am perhaps imagining. Thus looking for answers on how to fix / work-around.

  1. The sump has an iron cover. The ISM band ASK/OOK transmission cannot be detected, even 5 feet away, when the iron cover is closed. With the cover open, I am getting a decent range of about 20 feet, which is what I need.

  2. I had left the circuit installed for around 36 hours, and next day when I took the circuit out, I was surprised that it was still working and had not shorted out. It was full with in water-drops that had condensed overnight. The iron-sump cover is a dark shade of brown, and gets extremely hot during the day, in the sun. In the night, the temp drops significantly, and thus the result.

  3. Given how how it gets inside the sump in the day (I've not measured, but I'm guessing that it'd get like 50-60 deg, with relative humidity above 95%, in the sump), what can I expect about the life of my 4S AA batteries ?

Due to these challenges/observations, I am think of splitting the circuit into 2 parts, i.e. the ultrasonic sensor, mounted on a tiny PCB, with the soldered/exposed pins all potted with hot-glue. This part stays inside the sump. The rest of the circuit is housed outside the sump, in an IP66 type of enclosure. The enclosure kept outside, would let the RF TX work well, keep the batteries in saner temp, avoid excessive condensation. Of course, here the challenge is, how to wire the 2 parts together, as the wire coming out of the sump, will have to avoid being damaged by the sump cover crushing it, once closed tight. One problem with this is, I cannot keep the IP66 enclosure within 5 feet of the sump, so the wirelength might become an issue (?)

Should I alternatively, just do something to keep the RF TX antenna outside the sump ? But won't the wire of the antenna extension, alter the antenna behaviour (altered gain for the necessary frequencies) ? If I do this, I still don't know, how to address the water condensation issue. Or how well the batteries would do.

Edit: Finally, I am not sure, if the water condensation will (and how badly) impact the ultra-sonic range sensor itself, i.e. the transducers themself, as those need to remain exposed. I can imagine a drop of water (from condensation) hanging on the transducer and easily throw-off the readings completely. No ?

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bdutta74
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  • It's a complicated series of questions, observations and ideas – Andy aka Apr 28 '13 at 16:03
  • Yes @Andyaka, I understand. However, given the rich experience many community members here have, I hope to get some good and practical leads. – bdutta74 Apr 28 '13 at 16:07

1 Answers1

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I suggest you look at some of the marine solutions for depth sounders.

I don't think condensation will affect your readings as they produce weak near instantaneous echos which probably can't be detected.

Can you seal your system inside a pvc or other plastic type tube which could be inserted inside the sump? Transducers will work well as long as there is no air gap between the transducer and what you are measuring. So if you put the transducer in the bottom of a pvc tube, and poured epoxy around it (keeping out all the air bubbles) it should work fine. Then you could seal the rest of the electronics inside. You could even change the lid on the sump to be fiberglass or pvc with the sensor built in. The plastic will allow your ISM radio to broadcast outside the well.

user6972
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  • I'd think to get marine depth sender working it would need to be on a float on the water. – Nick T Jun 08 '13 at 21:34
  • No. Depth sounders can work through fiberglass/plastic/etc. as long as there are no air gaps. (Naturally the other side of the fiberglass/plastic/etc. has to be water you're measuring.) They loose a few feet of their close range sensitivity but they work fine. However in this application I only reference them in terms of how to seal them. – user6972 Jun 10 '13 at 20:56
  • I was thinking his water-level sensor would be at the top of the sump so there would always be an air gap. That's also what you seem to imply when you mention condensation on the sounder. – Nick T Jun 11 '13 at 00:46
  • Right. The air gap is only an issue when measuring fluid depth. He is measuring "air depth" which in his case he can leave the diaphragm exposed, but he can still seal the transducer in epoxy. – user6972 Jun 11 '13 at 04:50
  • In fact I think even when measuring air, the transducer could be completely sealed and function ok. It depends on the required amount of sensitivity because covering the transducer will reduce some of it's dynamic range. We just don't have enough details of his project to guess very well. The marine depth sounder analogy was only meant as an example of how to isolate a harsh environment from the transducer. I assume he googled a few to see what they look like.... – user6972 Jun 11 '13 at 04:59
  • I don't think a depth sounder is going to work well to measure an air distance; the acoustic impedance matching is going to be terrible/non-existent for air vs. fluids or other things with a density close to 1 g/cc – Nick T Jun 11 '13 at 20:58
  • @NickT Please forget the depth sounder analogy if it confuses you. The marine depth sounder analogy was only meant as an example of how to isolate a harsh environment from the transducer which was the OP's issue. – user6972 Jun 11 '13 at 23:04