On Sat, 10 Jan 2009 16:26:27 -0600, John O'Flaherty <quiasmox@yeeha.com> wrote:> On Fri, 09 Jan 2009 19:24:36 -0700, Eric Jacobsen ><eric.jacobsen@ieee.org> wrote: >>On Fri, 9 Jan 2009 10:28:44 -0800 (PST), Le Chaud Lapin >><jaibuduvin@gmail.com> wrote: >>>On Jan 9, 12:03�pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote: >>>> On Fri, 09 Jan 2009 11:44:03 -0600, "briang2000" >>>> >We've got a safety-related application where we'd like to determine if a >>>> >shower is running in the bathroom. �Does anyone have any suggestions on how >>>> >that determination could be made by sound?--snip-->>My concern with a DSP approach >>would be false alarms from other >>"noisy" things like hairdryers, bath fans, shavers, electric >>toothbrush, etc., etc. Discriminating one type of "noise" from >>another reliably can be pretty tricky. > > Combining a flow sensor and acoustical approach, a piezo sensor > attached to the pipe feeding the shower head would give a better SNR, > and still wouldn't be mechanical or require re-plumbing. I just tried > an automotive mechanic's stethoscope on a kitchen water pipe, and it > gives quite a loud hissing when the water is running, and not much > other sound. > The spectrum would shift some with water temperature and flow rate, > but it's a really strong signal. > If you could make it low-power enough to work from a lithium battery, > and using a wireless scheme, it wouldn't require any wiring inside the > shower stall.I do have one concern with a directly-connected audio transducer. Ever tapped on a radiator pipe? I know that both water and (metal) pipes are excellent conductors of sound; how much of a problem will a house with two showers present? That is, how much of the sound from S1 running will be picked up by the transducer attached to S2? This is one case where an "air pickup" might be better than mechanical coupling. Anyone have any relevant experience? Frank McKenney -- �The most exciting phrase to hear in science, the one that heralds new discoveries, is not �Eureka!� (I found it!) but �"That's funny..."� -- Isaac Asimov -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)
detecting white noise... shower running?
Started by ●January 9, 2009
Reply by ●January 11, 20092009-01-11
Reply by ●January 11, 20092009-01-11
On Sun, 11 Jan 2009 10:41:35 -0600, Frnak McKenney <frnak@far.from.the.madding.crowd.com> wrote:>On Sat, 10 Jan 2009 16:26:27 -0600, John O'Flaherty <quiasmox@yeeha.com> wrote: >> On Fri, 09 Jan 2009 19:24:36 -0700, Eric Jacobsen >><eric.jacobsen@ieee.org> wrote: >>>On Fri, 9 Jan 2009 10:28:44 -0800 (PST), Le Chaud Lapin >>><jaibuduvin@gmail.com> wrote: >>>>On Jan 9, 12:03�pm, Eric Jacobsen <eric.jacob...@ieee.org> wrote: >>>>> On Fri, 09 Jan 2009 11:44:03 -0600, "briang2000" >>>>> >We've got a safety-related application where we'd like to determine if a >>>>> >shower is running in the bathroom. �Does anyone have any suggestions on how >>>>> >that determination could be made by sound? >--snip-- >>>My concern with a DSP approach >>>would be false alarms from other >>>"noisy" things like hairdryers, bath fans, shavers, electric >>>toothbrush, etc., etc. Discriminating one type of "noise" from >>>another reliably can be pretty tricky. >> >> Combining a flow sensor and acoustical approach, a piezo sensor >> attached to the pipe feeding the shower head would give a better SNR, >> and still wouldn't be mechanical or require re-plumbing. I just tried >> an automotive mechanic's stethoscope on a kitchen water pipe, and it >> gives quite a loud hissing when the water is running, and not much >> other sound. >> The spectrum would shift some with water temperature and flow rate, >> but it's a really strong signal. >> If you could make it low-power enough to work from a lithium battery, >> and using a wireless scheme, it wouldn't require any wiring inside the >> shower stall. > >I do have one concern with a directly-connected audio transducer. >Ever tapped on a radiator pipe? I know that both water and (metal) >pipes are excellent conductors of sound; how much of a problem will >a house with two showers present? > >That is, how much of the sound from S1 running will be picked up by >the transducer attached to S2? This is one case where an "air pickup" >might be better than mechanical coupling. > >Anyone have any relevant experience?I just acquired some by experiment. I used the mechanical stethoscope I mentioned, and found that I couldn't hear any sound in the shower pipe when running nearby taps or the toilet, which come from the same source pipe. When listening to the shower pipe with the diverter valve feeding the water away from the shower, the sound was audible, but still much weaker than when the water was coming out of the shower pipe. The stethoscope is so constructed that it senses radial movement of the pipe wall. You can hear a poorer version of the sound with a screwdriver, with the handle end pressed into your ear, and the tip to the pipe. Why does the sound attenuate so much though there's a water/metal path? Maybe it's weakened by dispersion, especially at higher frequencies. Also, there isn't a continuous water path if the shower is in fact turned off, and the speed of sound in copper is about three times faster than in water, increasing dispersion. Finally, maybe the sound propagated over distance through the pipe isn't such as to make the pipe wall vibrate radially at higher frequencies. -- John
