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More  Liquid Sensors, Water Sensors,
Water Level Monitors



Water Flowing in Pipe Indicator -- July 6, 2009

The vibrations associated with water flowing through a pipe are picked up by an inexpensive piezoelectric wafer.  The signal from the wafer is first boosted by a micropower transistor Amplifier and then fed to an ultra low power voltage comparator.   When the vibration signal has sufficient Amplitude, a FET transistor switch is activated.  Drawing only 6uA, the whole circuit is powered by a lithium coin battery, which should power the circuit for many years.
The piezoelectric wafer is carefully sandwiched between a plastic enclosure, housing the battery and electronics, and the water pipe, using a nylon cable tie to apply pressure.  A bit of epoxy putty helps the assembly to conform to the pipe and couple more of the vibrations to the piezoelectric device.
The single resistor R7 defines the vibration sensitivity.  The resistor value can be selected so very low flow rates can be detected or ignored.  After the first voltage comparator circuit, a 1 second filter circuit is installed.  This forces the vibrations to be maintained for at least that long before the circuit changes state.  This filter circuit helps to ignore pipe impact noise.
One application for this circuit might be for an irrigation control system.  A positive signal from the flow sensor could be used by the control system to confirm that water is flowing.  In another application, the circuit could activate an alarm should flowing water be detected when it should not be flowing.

Click on Drawing Below to view PDF version of Schematic

Hobby CircuitWater Flowing in Pipe Indicator

More   Liquid Sensors, Water Sensors,
Water Level Monitors

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