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 (2016) STATUS:
IN PRODUCTION: The Infiltec Model INFRA-20 Infrasound Monitor is now available for $345.
VIEW THE LAST 24 HOURS OF INFRA-20 REAL-TIME INFRASOUND MONITORING:
click on Image for larger view
This infrasound display is updated every 5 minutes and is generated by an INFRA-20 that runs 24/7 inside the Infiltec factory warehouse.
The display was generated by the free AmaSeis seismic data logging/display software and the display updates are by Fling FTP software.
You can set up a similar online display with your INFRA-20 using the same software.
Click on display image to enlarge and update.
Even though the INFRA-20 is inside a building, it can detect the infrasound outside the building.
Each horizontal line covers 1 hour.
The oval shaped infrasound peaks (about 3 minutes long) come from freight trains as they pass within about 100 meters several times per day.
The rectangular infrasound peaks (about 10-50 minutes long) come from a gas space heater fan in the factory.
The short infrasound spikes can be caused by doors in the factory being opened and closed.
Wind is the most common infrasound noise, and it generally peaks during the daylight hours.
You can check the local weather and wind here.
The hours on the vertical axis are in Universal/GMT time, +4 hours ahead of local USA EST.
The data logging time base is corrected within milliseconds by the free program NetTime.
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/7/8/10 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: 15 ft (4M) 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/7/8/8.1/10 32 or 64) 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 port for supplied 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.
Other recent infrasound source detections by Infiltec include: freight trains, microseisms, compressors, and wind turbines.
UNDER DEVELOPMENT: A Portable Infrasound Generator .
Precise digital tuning within the 8 to 20 Hertz output in the Infrasound Range.
Controlled by a built-in variable frequency generator and driven by a powerful subwoofer amplifier
Powered by either house current 110-240 VAC or 12 VDC car battery
Portable by truck or van
Design follows Helmholtz resonator principles
Inexpensive compared to other speaker designs
Driven by powerful subwoofer speaker
Potential applications include: music augmentation, classroom/public demonstrations, evaluations of effects on people and animals, repelling birds, propagation studies, paranormal research, etc.
Contact Infiltec for latest development status.
Picture of prototype during testing (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
NetTime download, or
NIST Internet Time Service download
and download the free program. 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 this software
to reset the time every 10 or 15 minutes, and that
keeps your computer clock in synch.
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' seismic data logging software for Windows (free).
IRIS seismic data logging software for Windows, Mac, Linux (free).
What kind of computer do I need for microbarograph data logging?
We have free data logging software for Windows, MAC, and Linux computers.
Almost any PC with Windows XP to Windows 10 (32 or 64) will run the free
Amaseis seismic software.
We have tested it on Windows XP, Vista, 7, 8.0, 8.1 and 10 and 32 or 64 bits.
You can still use other Windows programs while
the AmaSeis data logging continues. You will need to have a connection to the Internet
to run the internet time correction software.
Most computers today do not have hardware serial COM port, so we provide a USB-Serial adapter cable that
can create a virtual serial COM port from a USB port.
There is a new free version of AmaSeis called
that works with Windows, Apple computers and Linux computers.
We are working on a Raspberry Pi system with Raspian and jAmaSeis that would replace the
requirement of using a PC or MAC to log INFRA20 data.
How can I prevent my AmaSeis program from stopping every few days?
Here are some suggestions listed in order of priority:
1. to keep AmaSeis
running 24/7 you MUST keep the AmaSeis 24 hour
"helicorder" display running full screen,
and NOT reduce it to the task bar by clicking on
"-" at the top right of the PC screen for more then a few
minutes. If you are running
another program while AmaSeis is running, then
you can cover up the AmaSeis screen. If you do
reduce AmaSeis to the task bar, then it may run
for a day or two, but it may halt randomly because
it can not keep up with the serial data.
2. You should also try setting
DECIMATE=9 from the Helicorder menu. When
the helicorder 24 hour data screen updates on the hour,
it has to rewrite the past 24 hours of data, and
there will be less load on the PC processor because
DECIMATE=9 will only redraw every 9th data sample. You
can experiment with other values of DECIMATE to see
how they effect your data display. Note that all the
AmaSeis display parameters like DECIMATE, GAIN
and the filtering parameters DO NOT effect the data recording
because AmaSeis always records the full INFRA-20
bandwidth. So you can go back and look at previously recorded data
with different decimate, gain and filter parameters.
3. Newer PCs with more recent Windows versions, faster
processors, more memory, and faster drives generally give
better AmaSeis performance. AmaSeis works well with
Windows 10. We have multiple instances of AmaSeis
working simultaneously on one Windows 10 PC. However,
we have also had single AmaSeis instances working 24/7
on Windows XP PCs.
4. There is a new version of AmaSeis called jAmaSeis
(the j is for java), and it is available for Windows, MAC,
and Linux. It seems to run well, but we do not have
as much experience with jAmaSeis as with AmaSeis. You
can download a free copy of jAmaSeis from
5. It sometimes helps to do some windows "cleanup" to
make sure that your Windows is running as smoothly as
possible. Especially if the PC has been running for
a long time with no software maintenance. You might try:
A).a registry cleaner like the free "Wise Registry Cleaner"
B) a file and registry cleaner like the free "CCleaner"
C) a file defragmenter like the free "MyDefrag"
How can I make AmaSeis time accurate to a few milliseconds?
You can make the time base on your computer more
accurate by downloading and running a free program that resets
your PC internal clock to universal internet time every 20 or 30 minutes.
Try NetTime download (I am using this), or
NIST Internet Time Service download
Note that AmaSeis only checks the PC time on the
hour, so the closer to the hour you can correct it, the better.
Also you must have an internet connection to use
How can I find the COM port that Windows creates when I plug in the USB-Serial adapter?
When you plug in the USB-Serial adapter, Windows will search for a
software driver, and if you are connected to the internet and you
have Windows 7 or newer, then Windows will find the latest version
of the Prolific adapter driver. However, if you have an earlier
version of Windows or you are not connected to the internet, then
you will have to load the Prolific driver from the CD that is
supplied with the INFRA-20.
Most of the time, the new COM port will be 1,2,3 or 4; so you can
enter each of these numbers into the AmaSeis COM port window, and then
restart AmaSeis to see if the COM port error message goes away.
If that does not work, then
to find the COM port that has been created by the driver
you can also use the free terminal program
When you run TeraTerm, click on the "serial" button, and then
look in the list of COM ports for one that says "Prolific".
Note that the adapter has to be plugged in when you run
TeraTerm for the COM port to appear. When you click on the
prolific driver you will see a stream of data if the USB adapter
is connected to the INFRA-20.
To set AmaSeis to the correct COM port, start AmaSeis and click OK
on the "cant find COM port" message, then click OK on the "no
data" message. Then click on the "settings" menu item and go down
and click on "COM port". Then enter the COM port number you found
with TeraTerm, and then restart AmaSeis so that it will save the
new COM port number as the default. When you restart it should
start running on data from the INFRA-20.
One other thing. You also need to set the DEVICE in the "settings"
menu. Select the INFILTECQM1 in the device settings, so that
AmaSeis will know what kind of seismometer it is processing.
What is the INFRA-20 serial output data format?
The INFRA-20 putput data format is serial 9600 bps, 8N1, ASCII records, no hardware control.
Each ASCII record is terminated by LF and CR characters (10 and 13).
Records range from +32767 to -32767 and zeros are added to keep
the record length constant, eg. +10 is sent as +00010.
The sampling rate is about 50 records per second.
Every 24 hours of operation, AmaSeis stores on your hard drive
about 10 megabytes @ 50 records per second.
What is the INFRA20 calibration?
Each record count is approximately 1/1000 Pascal sound pressure.
So 1000 counts is 1.000 Pascals. To convert to dB (SPL) you
can use the
For example, 1 Pascal is 93.98 db (SPL). This calibration is based on the
specifications of the INFRA20 components and is probably correct within 20%.
We are working on a more precise calibration and certification proceedure.
What is the minimum infrasound signal that INFRA20 can measure?
The INFRA20 electronic noise level is about 20 counts (20 mPa or 60 dB SPL) over the full bandwidth, and this
can be measured by cross connecting the ports on the internal differential pressure sensor.
The lowest ambient infrasound level over the full bandwidth that you can expect to record with the INFRA20
is about 30 counts (30 mPa or 63.5 dB SPL), typically during the middle of the night
when the wind is calm and there are no nearby infrasound sources.
The INFRA20 background noise level is low enough so that the microbarom peak at about 0.2 Hz
can sometimes be detected above the ambient noise when the wind is calm.
How sensitive is the INFRA20 to changes in elevation?
If you move the INFRA20 up or down by 1 meter, it will register a change of
12 Pascals, or 12,000 counts. This is because the INFRA20
is essentially a "leaky barometer" and it must be kept stationary in the vertical direction in order to avoid false infrasound signals.
The INFRA20 would probably not work well in a moving vehicle, and it would not work very well if it was being carried, for this reason.
How sensitive is the INFRA20 to temperature?
The INFRA20 mechanism contains a closed volume connected to a very small leak. If the temperature of this volume changes, then a pressure
will be created inside this volume that will equalized with atmospheric pressure by airflow through the leak. This pressure will interfere
with the interpretation of the infrasound signal. Therefore is it important for any temperature changes to the INFRA20 mechanism to be
slowly varying, so that the device can compensate for these pressure changes. The INFRA20 software is designed to compensate over minutes
to slow temperature drifts, but not for large temperature changes over short periods. If the INFRA20 is inside an occupied building, then
the temperature changes will probably not be a problem unless the device is in the path of a heater or cooler. Similarly, if the INFRA20
is outside then slow temperature changes will generally not be a problem. If you want to shield the INFRA20 from larger temperature
changes, then it can be placed inside an insulated box, like a lunch cooler, with thermal mass like water bottles to keep the
temperature changes slow. For permanent outdoor installations, burying the INFRA20 in an underground vault with moisture protection may provide
very stable temperatures.
How do you reduce infrasound wind noise?
Wind is the most common source of infrasound background noise, especially below 2 Hz. The nuclear test band treaty
infrasound monitoring installations have extensive spatial wind noise averaging systems consisting of many open sensor pressure ports spread out over
a wide area and manifolded together at the monitor input. See the Wikipedia article on infrasound for a
picture of an infrasound wind noise averaging array.
If the wind noise is uncorrelated at each port, you should expect a noise reduction of
about 1/squareroot(number of ports in array).
Other pictures of wind noise averaging systems can be found that use porous hoses, forests, piles of stones, etc.
Infiltec is working on designs for portable wind averaging arrays for the INFRA20 that use inverted metal
dishes for ports, or fishtank bubbler stones. Note that INFRA20 measurements can often be made from inside
buildings where the buildings themselves provide some measure of wind averaging. Similarly measurements can be made
from inside stationary automobiles with windows cracked open to provide some wind averaging.
Can the INFRA20 be used to detect infrasound from wind turbines?
Yes, the INFRA20 is in use worldwide to record and analyze wind turbine infrasound.
This type of infrasound appears to be generated by the turbine blades passing by the support structure,
and this blade-pass generally occurs about every 1.5 seconds, resulting in narrowband spectral
harmonics with frequencies that are multiples of about 0.7 Hz: 0.7 Hz, 1.4 Hz, 2.1 Hz, etc. This infrasound
signature spectrum can often be monitored from inside buildings. Infiltec can provide custom
modifications to the INFRA20 so that other acoustic recorders and data loggers can
access the unfiltered differential pressure sensor voltage data. This allows for the INFRA20
use with any acoustic analysis software and hardware.
Can the INFRA20 be used to detect infrasound from meteors?
We do not know of any INFRA20 meteor monitoring as of March 2016. But the INFRA20 should
be sensitive enough if it is combined with a suitable wind averaging array.
Here is the description of a university
meteor infrasound system that could probably be built with an INFRA20 monitor. It utilizes a porous hose
wind noise averaging system that is installed in a forest for additional wind noise averaging.
Note that if multiple INFRA20 are used for direction calculations, then custom software
may be required to calculate direction. Please let us know if you set up a meteor infrasound system.
Why does AmaSeis saftware sometimes indicate an INFRA20 sampling rate of ~50 samples per second (sps) and other times 16 sps?
Make sure the AmaSeis software display ALWAYS indicates an INFRA20 sampling rate of ~50 sps when you
are recording or analyzing data. 16 sps will cause analysis errors!
The AmaSeis software needs to ALWAYS be running the INFRA20 and recording data
when you are analyzing recorded data to keep the sampling rate at ~50 sps,
or else AmaSeis will set the sampling rate to its default value of 16 sps.
But 16 sps will will cause AmaSeis to calculate incorrect time and frequency
data analysis! This is true even when examining
data from the past from the AmaSeis recorded data base.
Unfortunately the AmaSeis stored infrasound data base
DOES NOT keep track of the INFRA20 actual
sampling rate of ~50 sps, so keeping the INFRA20 connected
to the pc and recording data will keep it at the correct
sampling rate of about 50 sps.
One way around this problem is to use your right mouse button to
block and SAVE AS data segments
of interest as .SAC format data files which will keep their
correct sampling rate. You can open these .SAC files
with the AmaSeis FILE OPEN command whether AmaSeis is recording
INFRA20 data or not. You can send these SAC
files to other AmaSeis users without worrying about
the sampling rate changing.