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Hour Meter Circuits Last Updated on:
Monday, October 03, 2011 06:07 PM
Circuits Designed by Dave
Johnson, P.E. :
AC Current Controls Hour Meter- Many systems require
routine maintenance based on machine operation time. The circuit
below is a simple way to turn on a hour meter whenever AC power is
supplied to the machine. An inexpensive snap-on current transformer
from Magnetics Inc, is used to detect the AC current. The output of the
transformer is fed to a voltage doubler circuit. When 0.5 AC amps or
more of current is flowing, the circuit generates sufficient voltage to
turn on the n-channel MOSFET. Once tuned on, the transistor routes
voltage to the hour meter. Some hour meters contain their own
battery, so no external power is needed. In those cases, the
transistor switch alone will turn on the hour meter. [Designed by David A.
Johnson]
Machine Vibration Activates Hour Meter - This circuit allows an
off-the-shelf battery powered digital hour meter to be turned on and off,
according to a machine's operation, without requiring a direct electrical
connection to the machine. Machine vibrations are detected by an
off-the-shelf piezoelectric wafer. The wafer is normally used as a sound
generator. The 3v power could be tapped from the hour meter's own lithium
battery or from a separate 3v lithium battery. The circuit only draws
about 1.5uA, so a 250mA-hr battery would power the circuit for about 10
years. Published in EDN, Jan 16, 1997
Machine Vibration Controls Hour Meter - This circuit allows an
off-the-shelf battery powered digital hour meter to be turned on and off, according to
a machine's operation, without requiring a direct electrical connection to the
machine. Machine vibrations are detected by an off-the-shelf piezoelectric wafer. The
wafer is normally used as a sound generator. The 3v power could be tapped from the
hour meter's own lithium battery or from a separate 3v lithium battery. The circuit
only draws about 1.5uA, so a 250mA-hr battery would power the circuit for about 10
years. Published in EDN, Jan 16, 1997 …. [Hobby Corner Circuit by Dave Johnson]
