Friday, September 27, 2013

Underground Leak Location (Failed, but interesting)

My brother has a water leak in the plastic line between his house and the street. We don't know where the pipe runs and haven't been able to find a wet spot. It's not a huge leak, so he can just shut it off at the meter most of the time.

Cool Little Amplifier

The first problem is locating the pipe, we know where it is on both ends, but there's 400ft and a concrete driveway in between.


  • I found ground penetrating radar first, but it would cost way more than just running a new pipe to buy and it's well out of my capabilities to build. Maybe in a few years, but we don't have that kind of time.
  • Metal detectors don't work on plastic pipe unless you put something metal in them (steel cable), which requires disconnecting the pipe. If we had a metal detector this would be a reasonable starting point. It's still on the table, but we have other options to try.
  • A smaller wire could be pushed down the pipe and connected to a small transmitter. Then a receiver would locate the signal and pinpoint the pipe.
  • With a ground microphone and an amplifier it's possible to listen to sounds under ground. A wrench or solenoid can be used to tap on the pipe, which will transfer down the pipe a ways and (hopefully) be audible near the pipes location. The leak may also be audible within a few feet.
Schematic - Pretty much exactly as in the source link

I've build a amplifier based on a circuit for an amplified ear I found on the internet. It seems to work good, but I'm having a real problem with the microphone. It will pick up sounds from all over, but nothing from the ground. I've tried several different ideas to transfer the sound, but so far I've come up dry. I think a piezo buzzer element is the key, and I managed to break the only one I had. I've got several more on the way, but it will be at least Saturday, probably Monday before I have them. We can't start digging before Monday (call-before-you-dig), so I'm hoping for Sat.

Prototype and RevA001 PCB

Results So Far

  • It's a really cool little amplifier, Q3 varies the gain of Q1 so that faint noises are highly amplified and loud noises have little amplification. If I can sort out the microphone problem it should work really well. It would also work great as an electronic stethoscope.
  • It doesn't seem to work as I intended to use it. I really need the digikey parts before passing judgement, but I think it should have a variable bandpass filter in it to isolate the desired noises. I can hear all kinds of stuff, but not what I'm listening for.
  • I ended up connecting a piece of wire to a fish tape, shoving it down the pipe and hooking a arduino clicking a relay that shorts a (low output) battery charger across the wire to transmit a clicking noise. I only had a 50ft tape so I couldn't trace much of the line, but it looks like a bee line. I used 30 turns around a cool-whip container (approx 15cm diameter) connected to the microphone input to listen for the clicks. It (barely) picks up the clicks, but AC lines are VERY obvious (loud buzz). I think I found the pipe and the end of the tape, but gave up as I didn't feel I was accomplishing anything. I could divide the pipe into (up to) 8 pieces and find the leak, but that would mean 8 potential future leak points (and 8+ holes to dig of unknown depth).
  • Unless the digikey parts are here tomorrow and I locate and fix the leak (unlikely) we're digging in a new line with a trencher on Monday. It's not looking good. I'm not shelving this project yet though, it would be very useful for locating noises in various equipment and it should work for finding pipes, if I can come up with a working mic. Perhaps I'll modify it for a bandpass filter too. 


  • R1 is specified as 10K, but my mic element specified 2.2K and worked much better with that. For the piezo transducer and the wire coil I disconnected the resistor.
  • The audio jack is connected with wires, I didn't have time to make a footprint for the one I had.
  • I did the PCB in a hurry, and I really should redo it, I make no promises as to it's performance.
Underside of PCB


No comments:

Post a Comment