DiscoverCircuits.com, has 30,000+ electronic
circuits, cross-referenced
into 500+ categories. We have searched the web to help you
find quick design ideas.
We make every effort to link to material posted by the designer.
Please let us if you would like us to link to or post your
design.
The contents &
graphics of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB
SITE server
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
