Basic Stamp Seismometer
By: Mark Spencer, WA8SME, former ARRL ETP Coordinator
A simple, yet capable, seismometer that teachers can use to
instruct the fundamental principles of seismology can be
constructed using a Basic Stamp and two Memsic 2125
accelerometers.
Each accelerometer has two axes. One
accelerometer for the X and Y-axes and
one accelerometer for the Z-axis were
used in the prototype. The Memsic
accelerometers are capable of measuring
up to +/- 2 gs with a resolution of about
.001 g. Taking into consideration the 32bit limitation of the Basic Stamp and the
2uS resolution for measuring pulse width,
the combo can resolve to around .002 g.
The seismometer was constructed on a
homemade circuit board. The X-Y accelerometer
is mounted flush on the main board. A ground
plane of copper allows a sub board for the Z-axis
accelerometer to be soldered perpendicular to the
main board. Scraps of circuit board material were
soldered in place to maintain structural rigidity.
Since there was one unused axis, the Z
accelerometer is mounted in such a way so that
the unused axis is oriented 45o to the X-Y axis for
later investigations (for example, verifying vector
sums).
The Basic Stamp is programmed to sample the
pulse width for each accelerometer axis channel.
A pulse width of 2,500 uS represents zero g.
Because of the Basic Stamp integer math
limitations, the pulse width is sent via the serial
port to a PC with StampDAQ software running.
The StampDAQ places the received data into
EXCEL where the full math and display power of
the PC can be used to manipulate the data and
create the seismograph displays. The power of
the EXCEL spreadsheet provides unlimited
opportunities for students to explore the data collected by their seismometer. The
program is configured to provide continuous measurements, 500 samples are displayed,
the graphs are clears, and the program loops back. The students may elect to program the
Stamp to wait for and “event” and
not begin collecting data until a set
g threshold is reached to trigger
collection, and another g threshold
to stop collection.
Alternatively, the seismometer
could be connected to the PC via a
data link transmitter/receiver pair.
The data could then be sent over
radio waves instead of the serial
cable.
The seismometer can be used to do
other acceleration collection tasks
besides “shaking dirt.” The Stamp could be programmed to store accelerations in ROM
and then dump the data to StampDAQ. The 9 volt battery power source makes the
seismometer a portable accelerometer that students can take on rides to study amusement
park physics. Or the seismometer can tag along for vehicular motion studies.
This simple, and inexpensive seismometer proves many opportunities for students to
study the science of accelerations. The hardware architecture matched with software
flexibility allows this instrument to be used in many, many different activities. If you
would like more details or copies of the software, contact the ARRL Education Services
office, [email protected]
© Copyright 2003-2010 American Radio Relay League, Inc. all rights reserved. This
content is intended for educational purposes. When used for this purpose, please
acknowledge ARRL as the source. Additional permission is required to use this material
in any training or product that will be redistributed or used for re-sale.
BStamp Seismograph
1.0K
9V
To StampDAQ
12
P11
P5
P10
P6
P9
P7
P8
3
YOut
Gnd
Vcc
XOut
Gnd
6
5
4
16
15
14
13
Transmitter Module
(for remote sensing)
Memsic
2125
o
5
4
Gnd
6
17
TOut
Vcc
2
XOut
1
18
Gnd
P4
P12
19
Z -X/Y Axis
(mounted perpendicular
to circuit board and 45
to X-Y axis)
11
P3
P13
20
3
10
P2
P14
21
YOut
9
P1
P15
T Out
8
Vdd
22
2
7
RES
Vss
PO
X-Y Axis
(mounted flush
with circuit board)
23
Memsic
2125
6
24
ATN
BStamp
5
Vss
1
4
Vin
SIn
Gnd
3
SOut
Gnd
2
TXD
Vcc
1