How to Build an Inexpensive Microbarograph.

Welcome to The Inexpensive microbarograph Project! See for latest page updates.

These pages describe my project to build simpler and less expensive amateur microbarographs by using microprocessors and other new chips, such as switched capacitor filters. I have tried to provide links to much of the excellent information that is already on the web. And I have tried to fill in some of the gaps in the existing information. For instance:

• Where do you get all the hard-to-find parts?
• What is the simplest & cheapest system you can build that will still detect 0.001 Pa signal.
• What is the bottom line cost, and how can you cut costs?

PROJECT STATUS:

• December 2006: Currently monitoring infrasound activity in the Washington, DC metro area from my prototype system installed in a cooler on the balcony of my condo. Redesigning the circuit board to use a variable reference voltage for the instrumentation amplifier to null out sensor and amplifier offsets. I can build copies of the electronics for $200 plus shipping if you are willing to be a Beta tester. The current system does not have a wind averaging array. Please if you are interested.
• December 2005: completed a beta design of my PCB, had some copies made, and added a diecast alumimum enclosure for thermal and electromagnetic shielding.
  

SPECIFICATIONS OF INEXPENSIVE MICROBAROGRAPH:

• System Bandpass: 0.01 to 4 Hz.
• High-Pass filter: ~100 sec or 0.01 Hz using volume/capillary tube.
• Low pass filter chip: 4 Hz anti-alias, 8 pole Bessel filter (MAX4701)
• Differential pressure sensor: silicon, bridge type, 1"wc (Honeywell DUXL01D, about $65) or an (All Sensors 1 INCH-D1-BASIC, about $36)
• Pressure Resolution: ~0.004 Pa - possibly lower depending offsets
• Pressure Range: +/- 120 Pa (32768 times pressure resolution)
• Amplifier: instrumentation,gain set to ~1000x, single supply, micropower, RTR out (INA122P)
• Power Source: ~2ma 5VDC, derived from PC serial port, no exernal power supply
• Voltage Regulator: 5VDC, low dropout micropower, precision (LP2950-5.0)
• Amplifer Reference Voltage: 2.5VDC fixed, precision reference (LT1004-2.5) or the variable regulator (LP2951).
• Microprocessor: 4mhz, with onboard 16 bit ADC and software serial I/O (PIC14000)
• Firmware: ADC sampling at ~35 SPS, zero drift tracking ~5 min TC.
• Enclosure: diecast aluminum box for shielding (Hammond 1590P)
• Serial Output: PIC14000 software RS232, 9600 baud, 8N1, ascii records, -32767 to +32767
• Wind Spatial Averaging: array of micro-perforated garden tubing
• Data Log/Display: freeware PC seismic log/analysis software (AMASEIS)

The Inexpensive electronics design uses an inexpensive silicon differential pressure sensor, together with 4 chips for the amplifier, 8 pole Bessel filter, 16 bit a/d, and serial output. It is powered by the PC serial port, and the serial data outputis designed to work with the freeware data logger/display program Amaseis.

Inexpensive Microbarograph Pictures (complete system with electronics and sensor)

• Exterior of microbarograph with serial cable
• Interior of microbarograph
• PCB removed from box
• PCB and high-pass pneumatic filter removed from box

Inexpensive Microbarograph Data Analyzed with AMASEIS Seismic Software

• April 24, 2006 infrasound 24 hour data plot with 3 events
• Expanded view of infrasound April 24, 2006 event A
• Expanded view of infrasound April 24, 2006 events B and C

• Infrasound Monitoring with a Microbarograph How to detect low frequency acoustic waves in the atmosphere.

• Bringing together seismology and atmospheric sciences by Läslo Evers. Includes How can infrasound be measured? that shows pictures of a microbarograph, and its field installation with wind averaging by a porous hose array.

• Infrasonic Symphony: The Greatest Sounds Never Heard from Science News, Week of Jan. 10, 2004; Vol. 165, No. 2 , p. 26.
• Infrasonic from the Wikipedia.

• NOAA Infrasonics Program

• The Infrasound network (ISNet): Background, design details, and display capability as a 88D adjunct tornado detection tool.

• 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 PicBasicPro or 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 AmaSeis 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 DataQ. Their $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 AboutTime 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 RighTime 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 shutdown. 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.

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.

• AmaSeis Alan Jones' data logging software for Windows (free).
• SEISAN, SEISLOG, SEISNET Institute for Solid Earth Physics software for Windows. Article describing Seislog.
• WinQuake Larry Cochrane's event viewing software for Windows ($35).
• SDR Larry Cochrane's data logging viewing software for Windows (free).
• EMON Ted Blank's data logging software for DOS (free).
• 6SMOWIN Mauro Mariotti's data logging software for Windows (free).
• Please 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.

• ACCELEROMETERS
  
  • Mesmsic thermal based accelerometer chip (comparable to Analog Devices)
  • Parallax accelerometer sensor uses Memsic digital output chip.
  • Analog Devices iMEMS®: Integrated Micro-Electromechanical Systems (ADXL105 & ADXL202).
  • ADXL202 Technologies and Applications.
  • ADXL202EB evaluation board (pdf) this packages the surface mount ADXL202 into a DIP package.
  • ADXL105 Technologies and Applications (improved version of ADXL05).
  • Crossbow packaged Analog Devices accelerometers.
  • PSN-L Email list comment of Scientific American article on using ADXL05 sensors for microbarograph measurements.
  • (pdf) Using the ADXL202/201 with the Parallax Basic Stamp Module to Speed Algorithm Development Analog Devices application note.
  • (pdf) Using the ADXL202 in Pedometer and Personal Navigation Applications Analog Devices application note.
  • Using the ADXL202 with a microcontroller.
  • Strong Motion Data on a ADXL05 Sensor quake data recorded from accelerometer.
  • ShakeMaps: Southern CA and Northern CA maps of acceleration magnitudes during recent quakes.
  • How to solder surface mount parts (like ADXL chips) using a toaster oven.
  • Brown Dog Component Adaptors DIP adaptors for surface mount chips.
  • Digikey: Surfboard adaptors to go from surface mount to through-hole (pdf file of catalog page).
  • ADXL 14 pin carrier board use my HP laser printer file to print circuit traces for a home brew board.
  • BasicStamp List messages about using the ADXL and surface mount chips.
  • DIY Air-pencil soldering iron how to make one for under $20.
  • Surface Mount Secrets

• ELECTRONICS RESOURCES
  
  
  BOOKS
  • Search enginz all about second hand book search, including book coupons.
  • Bookfinder compare used book prices.
  • BestBookBuys compare new book prices.
  • Amazon Art of Electronics by Horowitz and Hill (THE BIBLE!).
  • Amazon Active Filter Cookbook by Don Lancaster.
  • Amazon Troubleshooting Analog Circuits by Bob Pease (THE GURU!).
  • Amazon The Art and Science of Analog Circuit Design by Jim Williams.
  • Amazon Analog Circuit Design : Art, Science and Personalities edited by Jim Williams.
  • Amazon USB Complete: Everything You Need to Develop Custom USB Peripherals by Jan Alexson.
  • Amazon Serial Port Complete by Jan Axelson.
    CHIP SEARCH
  • FindChips
  • StockNet
  • QuestLink
  • ChipCenter
  • Need2Buy
  • USBid
  • CMB Components
  • Part Miner
    CATALOG/ONLINE SALES
  • DigiKey
  • Mouser
  • Hosfelt
  • Allied
  • Newark
  • Jameco
  • SimCo, OKW, SerPac, PacTec, Fibox inexpensive plastic enclosures.
    MANUFACTURERS/DATA SHEETS
  • Burr-Brown
  • Dallas Semiconductor
  • Linear Technology
  • Maxim
  • Microchip
  • National
  • Texas Instruments
  • Analog Devices
    MISC
  • Electronic Schematics on the Web
  • The Guru's Lair Don Lancaster's extensive links
  • GPS boards OEM board GPS for $79.
  • Newsgroups: sci.electronics.basics, sci.electronics.components and sci.electronics.design.

• MICROPROCESSOR RESOURCES
  
  • Circuit Cellar magazine for embedded control applications.
  • Microchip PIC 8-bit microprocessors
  • PicBasicPro for programming PIC microprocessors, and email list with searchable archives.
  • microCode Studio PICBasicPro Edition.
  • CCS PIC C for programming PIC microprocessors (user exchange).
  • Peter H. Anderson resources on PIC embedded processor control
  • Parallax Basic Stamp processors - I got introduced to microprocessors here
  • DataQ DI-151RS Low Cost, 12 Bit A/D Serial Port Starter Kit As Sold By Radio Shack.
  • Newsgroups: comp.dsp, alt.microcontrollers.8bit and comp.arch.embedded.
  • PIC Tutorial: Understanding & Programming the PIC16C84 A beginners' tutorial.
  • PICLIST email list for people interested in the Microchip PIC.

• MECHANICAL PARTS AND LAB EQUIPMENT SOURCES
  
  • ScienceLab lab equipment and chemical supply.
  • Rare-Earth Magnets sells new magnets.
  • ForceField sells recycled magnets
  • Hamilton Core Drill Bits neodymium magnets.
  • Grainger hardware distributor (magnets, etc.)
  • McMaster Carr hardware distributor (magnets, nuts, bolts, metals, etc.)

• SOFTWARE
  
  • AktivFilter software for designing perfect active filters with real components.
  • AmaSeis freeware microbarograph data acquisition program. Instructions for using Amaseis to analyze microbarograph data.
  • WinQuake microbarograph event viewing software. Instructions for using WinQuake to analyze microbarograph data.
  • Spectrogram 5.1 freeware audio spectrum analysis software.
  • FilterLab freeware tool that simplifies active filter design.
  • RighTime corrects the drift in your inaccurate PC clock.
  • AboutTime freeware uses the internet to precisely reset your PC clock.
  • TaskInfo shareware that monitors the resources used by PC programs.

• microbarograph
  
  
  BOOKS
  • Seismology Bibliography and Book Reviews.
  • Bookfinder search for used books on reading seismograms etc.
  • BestBookBuys compare new book prices.
  • Amazon Earthquakes Bruce Bolt, 1999 4th Edition - great introduction.
  • Amazon Earthquakes and Geological Discovery by Bruce Bolt, Sci. Am. Library, 1993.
  • Amazon Modern Global Seismology Lay and Wallace, 1995.
  • Amazon Quantitative Seismology: Theory and Methods Aki, 2001.
    OTHER
  • SemismicNet Redwood City Public microbarograph Network (extensive information!)
  • Lehman the man who built the first Lehman microbarograph described in the July, 1979 Scientific American Magazine.
  • Lehman Manual (PDF format) "Instructions for Construction of Lehman microbarograph by Kelly Knight - May 2000.
  • Newsgroups: sci.geo.earthquakes and microbarograph.general.
  • AZPEPP Arizona - Princeton Earth Physics Project

• GEOPHONES
  
  • Introduction to Geophones.
  • Infiltec QM-4.5 short period geophone microbarograph.
  • Geophone FAQ lists several manufacturers.
  • Geophone Model L-28 spec sheet (224k pdf).
  • Geophone Model L-15 spec sheet (205k pdf).
  • Walt's Geophone FAQs Selected PSN Geophone Postings.
  • Vault construction for your microbarograph by the Indiana University PEPP Program.
  • Vault construction for your microbarograph by the IRIS PASSCAL Program.
  • Improving a Geophone to produce a broadband microbarograph.
  • RT Clark sells used geophones.
  • Sercel parent company of Mark Products geophones.
  • eBay sometimes lists geophones.
  • NZ Geophone System Design shows circuit diagram and geophone mounting.
  • PSN equipment for sale may include geophones.
  • Simple procedure tests transducer EDN Magazine Design Ideas: March 1, 1996.
  • Remote 2-Wire Geophone Preamp Linear Technology design idea.
  • CablesToGo source for 25',50',100' extension serial cables for Infiltec geophone system (DB9, M/F).

• PRINTED CIRCUIT BOARDS
  
  • BPECS: PCB Circuit Design Package (very inexpensive.)
  • CADSOFT: Eagle PCB Circuit Design Package.
  • Electronic Assembly News list of pcb sources.
  • AP Circuits quickturn prototype pcb's for under $100.
  • EP Circuits quickturn prototype pcb's can include solder mask.
  • Olimex Ltd. in Bulgaria lowest proto prices, 2 week delivery to US via air mail. (4"x6" PCB, double-side, WITH silkscreen + solder mask, for $26 plus $8 Airmail)
  • Advanced Circuits good prices on production runs of pcb's.
  • Pulsar great prices on production runs of pcb's.
  • NeatSite links related to PCBs.
  • Making Printed Circuit Boards book by Jan Alexson.
  • How to Make PCBs This is how I make them.

• OTHER INTERESTING BUT LESS RELEVANT PAGES
  
  • SoPrePlaTec (pronounced "soapy platex") The Society for the Prevention of Plate Tectonics.
  • Sensors an awesome link page!
  • Vernier Science Hardware and Software for the Classroom.
  • Tinkers Guild Resources for Hands-on Science - sells CD of projects from the Scientifc American Amateur Scientist column.
  • Society for Amateur Scientists online projects and supplies.
  • Detecting Extraterrestrial Gravity by Shawn Carlson, from the January 2000 Scientific American Amateur Scientist Column.
  • Detecting Micron-Size Movements by Shawn Carlson, from the August 1996 Scientific American Amateur Scientist Column.
  • Earth Songs If humans had radio antennas instead of ears, we would hear a remarkable symphony of strange noises coming from our own planet.
  • Infrasound Monitoring with a Microbarograph How to detect low frequency acoustic waves in the atmosphere.
  • Crackpot Inventor original electronic devices, tools for clockmaking and repair, and a variety of other unusual handmade products.
  • Mad Scientist Network the laboratory that never sleeps.

• SOME OF MY OTHER INTERESTS
  
  • Join the SETI@Home search for extraterrestrial intelligence. Here are my statistics. Please join my team Dickster.
  • Join the Einstein@Home search for gravitational waves. Here are my statistics. Please join my team Dickster.
  • Join the Predictor@Home predict protein structure. Here are my statistics. Please join my team Dickster.
  • Join the SIMAP@Home compute Similarity Matrix of Proteins. Here are my statistics. Please join my team Dickster.
  • Join the Rosetta@Home determine the 3-dimensional shapes of proteins. Here are my statistics. Please join my team Dickster.
  • My Business Page Infiltec Air Leakage Control.
  • My Other Link Page building science, books, travel, etc...
  • My fun page jokes and travel photos.
  • My Gold Prospecting Near Washington, DC Page.
  • My SID-GRB@home how to build a simple VLF radio receiver that can detect Gamma-Ray Bursts (GRB) from the edge of the universe.
  • My How to build an inexpensive seismometer for earthquakes worldwide.