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2014-03-25:DAV: first public posting.
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safe
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make visible some of the normally-hidden workings of the human heart
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open source hardware
The various electronic subsystems can be arranged to build:
- Open source Holter monitor: able to scale down to a standard 4 electrode Holter monitor. Comfortable -- lightweight even including the batteries. Long run-time. etc.
- Open source body surface potential mapping: able to scale up to record from dozens of electrodes simultaneously. (The so-called "12-lead EKG" has 10 electrodes.)
Body surface potential mapping is the original motivation for the openheart project.
DAV and Dr.K wanted some body surface potential mapping data in order to test out some theories and heuristics and ideas we had for approximate solutions to the inverse electrocardiography problem. Off-the-shelf devices for recording body surface potential data were beyond DAV's budget at the time, but DAV's experience with mixed microcontrollers and data acquisition made him think it that one could be built for a more reasonable price.
The inverse electrocardiography problem is the problem of making a 3D picture of the electrical activity of the heart, when all we have is the body surface potential data.
DAV is buying the first prototype PCBs from OSHPark (Open Source Holter (OSH), OSHPark -- see the connection?)
We thought about using the acronym IEKG -- Improved Electrocardiogram -- but the "Institut für Ethik und Kommunikation im Gesundheitswesen" (the institute for ethics and communication in health care) already used the acronym IEKG.
Still looking for a catchy acronym.
- the open-hardware Holter heart monitor (OHHHM).
Other open-source EKG systems:
Biometric daughter board for Hoarder board The daughter board allows the hoarder board to collect EKG, EMG, EEG, skin conductance, and temperature signals. http://vadim.oversigma.com/Hoarder/Biometrics.htm Hoarder aka Swiss Army Knife (SAK) board, http://vadim.oversigma.com/Hoarder/Hoarder.htm http://capsil.org/capsilwiki/index.php/Hoarder_Board (_) designed as a part of the Every Sign of Life project. http://vadim.oversigma.com/esl/esl.html
The Hoarder Biometric daughter board uses a INA2321EA instrumentation amp and some OPA4336EA op amps to amplify a EKG EMG EEG signal.
SHIELD-EKG-EMG open source hardware which allows the Arduino and shield-compatible Arduino-like processor boards to capture electrocardiography and electromyography signals. https://www.olimex.com/Products/Duino/Shields/SHIELD-EKG-EMG/open-source-hardware
Schematic and board layout released under Creative Commons Attribution-Share Alike license.
input protection circuit
instrumentation amplifier: INA321EA TLC277IDR for DC removal
followed by MCP607 op-amp with gain control pot
No ADC on the board -- feeds the analog signal into the Arduino A0 analog input. (The Ain-sel header can be hardwired to feed the analog signal to any Arduino analog input).
instrumentation amplifiers: http://www.mouser.com/Semiconductors/Integrated-Circuits-ICs/Amplifier-ICs/Instrumentation-Amplifiers/_/N-6j73w/ (_)
OpenEEG-related software http://openeeg.sourceforge.net/doc/sw/
Ajay Bharadwaj. "Accurate ECG Signal Processing". http://www.cypress.com/?docID=28762 http://www.eetimes.com/document.asp?doc_id=1278571 (_) mentions that tyical ECG signals at the electrode include
- typically DC +-300 mV half cell potential offset with Ag/AgCl electrodes
- typically ~1.5 V common mode 50 or 60 Hz noise picked up from power lines
- typically +-0.5mV actual desired signal (p. 2)
- typically +-2 mV desired signal 0.05 to 150 Hz. (p. 3) The standard EKG paper (with 1mm small square boxes, 5mm large square boxes) runs at 25 mm/s 10 mm/mV
"ECG and EEG Applications: Quick Reference Guide" http://www.ti.com/lit/sg/slyt416/slyt416.pdf via http://www.ti.com/solution/ecg_electrocardiogram (_) mentions ADS1291 ADS1292 2-channel Holter ADS1298 12-lead ECG systems OPA334 zero-drift, low-offset, single-supply op amp OPA335 zero-drift, low-offset, single-supply op amp INA333 low-power instrumentation amplifier: 50 nV/sqrt(Hz) www.ti.com/sc/device/INA333
http://www.ti.com/solution/ecg_electrocardiogram (_)
mentions
When a low resolution (16 bit) ADC is used, the signal needs to be gained up significantly (typically 100x - 200x) to achieve the necessary resolution. When a high resolution (24bit) sigma delta ADC is used, the signal needs a modest gain of 4 - 5x. Hence the second gain stage and the circuitry needed to eliminate the DC offset can be removed.
"Stephen Lee and John Kruse" "Biopotential Electrode Sensors in ECG/EEG/EMG Systems" http://www.analog.com/static/imported-files/tech_docs/ECG-EEG-EMG_FINAL.pdf mentions Ag/AgCl has a relatively low half-cell potential of abou 220 mV. With properly prepared skin, body to electrode impedance is typically about 5 kOhm ... 500 kOhm is encountered frequently ... The cardiac signal (differential voltage across a person's chest) is typically 1.8 mV riding on a DC offset of up to 300 mV. ??? "The input bias current of the front-end amplifiers can polarize the electrode" ???
http://www.analog.com/static/imported-files/overviews/Home-Is-Where-The-Heart-Is.pdf mentions Analog Devices ADAS1000-3: 3-lead ECG analog front end (AFE) Analog Devices ADuCM360 fully integrated, 24-bit data acquisition system