SHAKE, RATTLE, AND ROLL
VIBRATION
By Ron Newton
MONITOR
Build one for
less than $10!
One of my students in
Kenya, Africa needed a
suggestion for a project that
would be simple and
inexpensive! I suggested a vibration
monitor that could be used as an
intrusion alarm. To make sure that it
would work, I built my own. Since
project cases always drive up the price
of a project, I thought, “Why not put
the project into a battery holder?”
Methodology
The detection transducer used here is a Measurement
Specialist, Inc., LDT0-238K piezo film sensor that has a
weight attached. This sensor can generate up to 70 volts
when stressed and produces an AC current when
vibrating. I found that very small vibrations produced small
voltages that needed to be amplified, so I selected a
Microchip MCP601. This is a 2. 7 volt single supply
amplifier and I used it in a non-inverting 101 amplification
configuration.
Eagle Plastics makes a three AA battery
holder with a switch. I designed a circuit
board the size of a AA battery that
would hold all the components (total
of nine), and used the center battery
slot to power and hold the board.
R1 Amplification = 1 + R2 = 1 + (100,000/1,000) = 101 ( )
By changing R2, you can increase or decrease the
amplification. The board is designed to either use a fixed
resistor or a potentiometer so that you can change its
sensitivity. The voltage from the sensor is limited by using
two signal diodes with opposite polarities in parallel,
and feeding the sensor’s output into an op-amp (see
the schematic).
June 2010 33
