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Circuits designed by David Johnson, P.E.
Last Updated on:
Friday, March 23, 2012 08:51 AM
Master Category List -
Dave's Circuits
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Hour Meter
Circuits |
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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.
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- MACHINE
VIBRATION TRIGGERS 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
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Hour Meter
Circuits
Master Category List - Dave's Circuits
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