Earlier this summer my son-in-law John and daughter found themselves with a bad problem in the basement of their home. Tree roots had gotten into the sewer main leading from their home and one day the water stopped draining. Unfortunately the water backed up onto their newly installed laminate wood floor and before the disaster was over much of the floor had to be replaced. Last weekend, while at our home for a Labor Day get together, John asked if I could come up with anything that would give him a warning should the roots grow back. I would love to have John come over and do some electronics with me but he is very busy with his work as well as being in the Air Force Reserve which takes up a lot of time. I decided that I would have to get the ball rolling and I will probably have to do much of the work on my own but this is something that he really needs and perhaps I can get the project to the point where he can come over and assemble the system like a kit.
Here is the schematic plan that I came up with to provide a simple alarm for the backing up of water in the sewer. Fortunately he has a clean out situated at the low point in the system where we can put a couple probes that can normally sit above drain water level but will be the first to be contacted with backup should the pipe become clogged again.
The circuit will be powered with a 10V to 12V wall wart. There is a green power LED to confirm that the unit is on. The sensor interpretation circuit is a simple LM393 comparator that drives an N channel MOSFET which in turn powers a flashing LED and a Piezo buzzer which is pulsed at about 2 Hz by a 555 timer circuit. An SPDT toggle switch allows the operator to turn off the audio alarm but this also turns on a red LED which gives notice that the audio circuit is no longer on line. This circuit has been bread boarded and tested using plain water in a beaker.
When power is applied to the circuit but the circuit to the sensor is open we get only the Green Power light. See below.
Connection of the wire to the sensor probes whose ends are in water triggers the alarm which powers the RED / BLUE flasher LED and the buzzer. Imagine you can hear the beep beep beep ...
Since the beep beep beep drives me crazy I have switched the toggle and the beeping stops but the red warning LED is now lit and since the water condition is still present the Flasher ID continues to flash.
I will have to wait for John to find time to come over to OK the continuation of this project but since I had some extra time this evening I decided to begin the process of blogging about it. I will add to the blog right through to the finished unit if it goes any further than these preliminaries. Since the problem of backing up water could be a universal problem and this solution is not complicated feel free to make one for yourself and post a picture of your unit so I can see what you made.
John W.
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