Detailed information on a low-cost design for a microbarograph that
can detect and monitor infrasound (sound under 20 Hz). This design makes
infrasound detection available for schools, businesses and amateurs.
Welcome to The Inexpensive microbarograph Project! This infrasound monitor project is designed to
make it possible for schools, businesses and amateurs to detect, measure and monitor the infrasound in
their environment. See for latest page updates.
CURRENT (2015) STATUS:
IN PRODUCTION: The Infiltec Model INFRA-20 Infrasound Monitor is now available for $345.
HOW TO ORDER:
Option1: FILL OUT OUR
ORDER FORM AND SEND IT TO US (form includes our most complete set of ordering options)
Compute the cost of your order on the form. You can pay by credit card, wire transfer,
check (may require delays for clearing) or money order payable to Infiltec.
Factory Address: Infiltec Instruments, 108 South Delphine Avenue, Waynesboro, VA 22980, Phone (540) 943-2776, Fax (540) 932-3025.
Option2: ORDER FROM PAYPAL:
Option3: CALL INFILTEC toll free (888) 349-7236 or (540) 943-2776 Weekdays 7 AM - 4 PM Eastern USA Time.
Option4: ORDER FROM eBay (eBay may have the best international shipping options)
Microprocessor firmware adjusts for component drift due to temperature
changes, aging, etc.
Very low power (under 0.05 Watts) operation. Designed to operate
Connects to PC DB9 serial port, or a USB port through a USB-Serial DB9
Works on Windows 98/XP/Vista/7 PC via AmaSeis logging data 24/7 in
background. You can use your PC for other jobs while AmaSeis is running.
SPECIFICATIONS FOR THE INFRA-20
Performance: Resolution is 0.001 Pascals (0.01 microbar or 0.0075 millitorr) over the range of + or - 25 Pascals (250 microbars or 187.5 millitorr).
Mode of Operation: Microbarograph design with solid-state differential pressure sensor and high-pass pneumatic filter.
Output: Serial output formatted for AmaSeis seismic software, RS232 9600 baud N81 ASCII, 50 samples/second.
Frequency Pass-Band: 0.05 Hz to 20.0 Hz bandwidth digitized and stored on hard drive by AmaSeis at about 10 megabytes per 24 hours of operation.
Temperature Range 40 to 90 F (4 to 32 C) with no adjustments required. Internal firware automatically adjusts for drifts. Requires constant temperature during operation that can be provided by insulation such as a small cooler.
Housing: Diecast aluminum box encloses all electronics and sensor, 6.024x3.268x1.988 inches (153x83x50.5 mm). Shipping weight 2.2 lb (1 kg).
Computer Connection: 10 ft (3M) serial cable (up to 100 ft (30M) extension optional) connects to PC DB9 connector or USB-Serial DB9 adapter.
Adjustments: No leveling, alignment, damping, gain, zeroing, etc adjustments required.
Power Supply: No external power supply required, all power (under 0.05 Watts) is supplied by PC serial port through the serial cable connected to the PC.
Digital Processing: 16 bits voltage resolution from internal digitizer, 50 sample/second ASCII output, firmware adjusts for component drifts.
Lowpass Filter: Very steep analog 8 Pole elliptic filter with 20 Hz corner frequency for anti-aliasing.
Software: Windows PC based seismic data logging and analysis software AmaSeis available online for free download. Includes spectral analysis and bandpass filtering functions.
Computer Requirements:PC running Windows (98/XP/V/7) can run AmaSeis in backgound while doing other tasks. Hard drive that can store 10 megabyte/day during 24/7 operation. DB9 serial port or USB-Serial adapter.
SAMPLE DETECTIONS BY AN INFRA-20 SYSTEM:
Click here for a typical 24 hour AmaSeis display on a calm day.
The red outline is around a typical helicopter infrasound signal
with two other helicopter signals next to it.
The green outline is around typical wind noise data.
And the blue outline is around a typical spike signal for a door closing
in the adjacent building.
Here is the red outline helicopter infrasound signal expanded AmaSeis display.
Note the peak amplitude is about 1000 counts which corresponds to 1 Pascal (10 microbars) because the INFRA-20 resolution is 0.001 Pascal (0.01 microbar) per count.
Here is the AmaSeis power spectra of the red outlined helicopter infrasound signal. The power peak is around 17 Hz but it is spread out because of +/- doppler shift as the helicopter goes by.
Note the steep roll off of the 8 pole elliptic 20 Hz low pass filter used in the INFRA-20 for anti-aliasing.
UNDER DEVELOPMENT: A Portable 8Hz-20Hz Infrasound Generator built into the lid of a steel drum (click on image to enlarge).
FILTER CHIP -
MAX7401CPA 8th Order, Lowpass, Bessel, Switched Capacitor Filter
low pass cutoff is configured with one external capacitor. I generally use
a cutoff of 4.5 Hz for infrasonics.
This chip requires 5 volts, single supply, 2 ma. The -3 dB filter cutoff (Fc2)
in Hz is determined by Fc2=.380/C where C is the capacitance in ufd.
For example, when C = .380 ufd, then Fc2 = .380/C = 1 Hz. The output
of a switched capacitor must be filtered to remove the switching
noise that peaks at 100 times Fc2 for this chip. I generally use
an RC filter with an Fc3 that is about 1.5 times the chip Fc2.
For 4.5 infrasound I set Fc3 to
about 6.8 Hz.
A/D & PC INTERFACE CHIP -
PIC14000-04/SP Programmable Mixed Signal Controller
programmed with firmware that I wrote to configure IC pins for 16 bit A/D, and for serial output to a PC. This chip requires 5 volts, single supply, 0.5 ma.
PIC 8-bit microprocessors can be programmed in firmware written in languages like
CCS PIC C.
You might be able to use a
Basic Stamp BS1 or BS2 processor
with an external A/D chip in place of the PIC14000. However, these
processors and the a/d chip may use too much power to use the serial
port as a source of power.
PCB LAYOUT AND NOISE REDUCTION -
In order to get 16 good a/d bits, the circuit board must be laid out so
as to minimize noise. All grounds must go to a central terminal
point in a "star" configuration. All chips must have bypass capacitors
on their power pins. In addition, the PIC14000 is programmed so that it goes to
"sleep" during a/d operations to minimize digital noise in the circuit.
SAMPLING RATE -
The 4 MHz PIC14000 can perform 16 bit A/D at about 60 samples per second (SPS) and
these samples can be averaged in software for noise rejection. I have written the firmware
to allow for a dip switch selection of averaging times from 4 SPS to 35 SPS.
SERIAL DATA FORMAT -
Each output sample is an ASCII record terminated by LF and CR. The samples range from
-32767 to +32767. This format can be read by the
seismic data acquisition program. Output from Amaseis can be further
analyzed by the
WinQuake seismic event viewing software.
A/D CONVERTER OPTIONS -
I use a microprocessor ADC to generate the serial data that Amaseis
can process (the input ASCII records looks like +3, -2, +8 .....) but if you are
not a microprocessor guru you can get a PC serial port data aquisition kit from
$24.95 DI-194RS Starter Kit is
4-Channel, 10-Bit, ±10V ADC. And the
$149.95 DI-154RS Starter Kit is
4-Channel, 12-Bit, ±10V ADC.
Note that the DataQ does not include
a lowpass anti-alising filter.
The Amaseis program has been modified to work with DataQ units.
TIME SYNCHRONIZATION You will need to get an accurate time reference to
Coordinated Universal Time (UTC)
(Greenwich England time without daylight saving time) since you want
to know the arrival time of events within a second
of UTC. Some folks hook their electronics to GPS or WWV radio
systems but I am too cheap for that. I looked for
some way to make my PC clock accurate to within
a fraction of a second per week instead of its usual
several seconds per hour of error. Here is what I
came up with:
1. Go to the Windows control panel under "Date/Time" and set your
computer to GMT with no daylight savings time.
Right now (winter) this is 5 hrs earlier than Eastern Time. It is not
too much trouble to work with a PC set to this time.
2. Go to
and download the free program "About Time 4.8". This Windows program
finds the reference time on the web and resets your
computer clock to it. It even corrects for the travel
time of the web packets. Set your clock within a
few ms of UT with this program. If your computer has
a dedicated web connection, you can set AboutTime
to reset the time ever 10 or 15 minutes, and that
keeps your computer clock in synch. However if you
do not have a dedicated web connection, then you want
some way to adjust your internal PC clock to an accuracy
of a fraction of a second per week. Go to step 3 to
find out how to do this.
3. Go to
and download the shareware program RITM514.Zip. This program
only works for DOS of Win95-98, not Win2k. It
makes changes in your autoexec bat and each time
you correct your PC clock, it makes the PC clock
error smaller. I have been able to get my data logger
PC to within a fraction of a second per week accuracy.
I have found that you must install this program in
the DOS mode that you get into from the Win95-98
It took me about a week of these corrections to get my PC
time reset accurately. Rightime has a free trial period
that you should use to see if it works for your computer.
I have had success in 3 out of 4 PCs. My AMD Althon 850
does not seem to work with RighTime, so far.
USE OF SEISMIC DATA PROCESSING SOFTWARE FOR MICROBAROGRAPHS
I found when I started my project in 2000 that most of the
existing seismic data logging software was programmed
to accept data from a few PC a/d boards, and most of the
programs did not accept the ASCII data records that
microprocessors can easily output. However I found one
program that the author was willing to modify to accept
simple ASCII records: the freeware program Amaseis.
Here is all of the seismic software that I am have
heard of that might be of interest to amateur seismologists.
Please send me links to all the software I have missed.
Alan Jones' data logging software for Windows (free).
Larry Cochrane's event viewing software for Windows ($35).
Larry Cochrane's data logging viewing software for Windows (free).
Ted Blank's data logging software for DOS (free).
Mauro Mariotti's data logging software for Windows (free).
if you know some other software that I should list here.
I started on some Visual Basic software for data logging, but I have not had
much time to work on it. Perhaps we need an open software project to develop
seismic software. Please
if you have some interest in this type of project.
What kind of computer do I need for microbarograph data logging?
Almost any PC with Win 98/XP will run Amaseis, Winquake, RighTime and AboutTime.
I use an old 2GHz Athlon with Win98 and 1Gbyte of free disk space.
This computer can run Amaseis at 35 samples per second input in the background,
plus Seti@home, and I can still use Winquake or other Windows programs while
the data logging continues. You need to have a connection to the Internet
to run the time correction program AboutTime. Note that Win2000/XP will NOT run the time
correction program Rightime since it
requires a modification of the (nonexistent) autoexec.bat file. Some new computers may
have USB ports instead of the older serial ports that the DataQ and microprocessor
serial input devices require, but you can generally
add a card that has these older COM type serial ports.