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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. |
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Click on Drawing Below
to view PDF version of Schematic |
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