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Publys: An open source biosensing board

Publys is an open source platform for the study and processing of bioelectric signals.

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Publys is an open source platform of bio sensors that can measure:
• ECG signals
• EMG signals
• Blood pressure
• Temperature
• GSR/skin conductance (stress)
The system can be used for different applications and is completely open to the whole community, both software, hardware and all documentation for manufacturing.

The bio sensors board has the following advantages:
• It is a low-cost system for bioelectric signals acquisition.
• Have low cost sensors for acquisition of ECG and EMG signals.
• Have an application of myoelectric signals for the control of man-machine interfaces.
• Contribute to the dissemination of open science.
• Access to low-cost scientific tools for the area of bioelectronics.
• Complete access to documentation that allows the development of new educational platforms for the acquisition of bioelectric signals.
• A portable development platform.

The problem:

Students or researchers who work with the acquisition of bioelectric signals constantly require specific equipment that is usually expensive and sometimes the institutions do not allow the free use of them. This great problem slows the development of new medical devices and sometimes discourages researchers.

Proposes solution:

A bio sensor development board based on the premises: low-cost, open source and portable, it becomes a fundamental tool to increase the number of investigations in the development of medical devices that allow to monitor vital signs in people or even animals.

Publys will be a device that opens the doors for researchers or students of Bioengineering to participate in health research. With the Publys platform, a tool is provided that allows the design of more advanced devices based on biosensors that can measure the biological, chemical and physical signs of health.

Open science is of vital importance to accelerate the pace of discovery and the continued funding of academic research. The closed science model leads to a profoundly inefficient, slower and more difficult progress.

The Publys development platform will be accompanied by a web page which will become a resource that allows sharing technology, educating with open documentation and placing science within everyone's reach. Publys proposes access, usability, replicability and improvements for scientific instrumentation in the development of applications based on biosensors, contributing to the dissemination of Open Science.

The Publys board can be employed for the following areas of study: bioelectronics, biomedical, neurophysiology, cardiovascular systems, electronic, electromyography and blood pressure.

Publys V1.0

The platform of development for the taking of bioelectric signals will be called from now:  Publys V1.0, the same one consists of several sensors dedicated to the acquisition of signals and data of diverse physiological parameters such as: ECG, EMG, GSR, temperature and blood pressure.

Publys V1.0 will use an Atmega328P microcontroller, which will allow to process the acquired electrical signals. Being the first version and fulfilling the purpose of an experimental prototype, the Atmega328P will be used because it is a low-cost and easily accessible device, but for a future version 2.0, the microcontroller must be replaced by one with higher performance and a higher performance security level.

Thinking of generating applications of low consumption and also portable, the Atmega328P was chosen since it can be powered with a lithium battery of a cell and a voltage of 3.7V. Publys V1.0 will additionally have Bluetooth LE integrated, to facilitate the transmission of data with a portable PC. The work environment is designed so that any beginner in electronics can use the board without major complications.

Note: The Publys board will not be certified as a medical device because it does not meet all the requirements of the FDA. The device at the time of manufacture must be used at the user's risk. However, the design of the sensors is designed not to exceed leakage currents greater than 10uA and must not place the user at risk.

Publys_Project - Project.pdf

PDF of the Publys project

Adobe Portable Document Format - 14.67 MB - 04/12/2018 at 14:59

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EMG sensor.jpg

Diagram schematic of the module EMG

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ECG sensor.jpg

Diagram schematic of the module ECG

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Publys Project.rar

Files design CAD (DesignSpark PCB)

RAR Archive - 21.29 kB - 04/07/2018 at 16:45

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Publys Library.rar

Library of the Publys project. For the software DesignSpark PCB

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  • 2 × AD8232 Semiconductors and Integrated Circuits / Misc. Semiconductors and Integrated Circuits
  • 1 × Atmega328P Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × 4.7uF Capacitor
  • 1 × 10uF Capacitor
  • 1 × 47nF Capacitor

View all 14 components

  • Project advances expected

    Ever2 days ago 0 comments

    For the moment I have explained the development of the EMG and ECG sensors. In the next few days I will be addressing the development of the other three sensors that the Publys board should carry, which are: Blood pressure, temperature and GSR.

    The design of the schematic diagram of the complete project is not finished yet, details are missing to add, I hope to work on it soon and be able to have the complete schematic diagram in less than a month.

    At the end of the schematic diagram I must start designing the PCB, apply DFM techniques in order to have an optimized prototype for large-scale manufacturing, however the first prototype will be a bit large (estimated dimensions 100mm x 70mm). For the second prototype the size must be reduced.
    For this project I have no plans to design a plastic enclosure  since it escapes my knowledge, I will just look for a plastic enclosure to which the PCB can be adapted.

     I will choose to look for one in the China market. As a future work, I should work on creating a more professional and personalized plastic enclosure, which can highlight the physical aspect of the product to be built.

    I hope to talk soon about the choice of electrodes and how they can impact the quality of the signals that are obtained.
    This project is divided into 3 parts:

    Part 1 of this project includes all the hardware design and files for manufacturing. Cover theoretical aspects of the functioning of the device and document the process necessary for manufacturing. Estimated time of work: 2 months. At the moment there is an advance of 40% in this phase of the project.

    Part 2: I hope within a month and a half to start phase 2 of the project, which consists in developing all the software that the Publys platform requires for its optimal functioning. I decided to leave it for after having the hardware developed, since for me it represents the biggest challenge of the project, I am not a software specialist, but I understand everything that must be done.
    I have researched a lot and there are many applications of algorithms based on open source that I can use and I will only need to make adaptations. This is the most experimental part of the project. Some hardware modules I have tested separately and they work. Estimated time of work: 2 months. At the moment 0% of advances.

    Part 3: Hardware, Software and Mechanical Integration. This is the last phase of the project and must carry a work period of 1 month. Integrating the hardware and software will be done in a simple way. I should spend time getting the plastic mold I plan to use for the device. Subsequently, I must work on testing all the sensors contained in the Publys platform. Estimated time of work: 1 months. At the moment 0% of advances.

    This is the basic structure of the project, as it progresses it may undergo modifications and even extend its range of scope.
    My efforts will be focused on designing a portable and low-cost platform that streamlines research for the development of new electronic devices in the E-Health sector.


  • EMG sensor

    Ever04/12/2018 at 15:22 0 comments

    "Electromyography (EMG) is an experimental technique concerned with the development, recording and analysis of myoelectric signals. Myoelectric signals are formed by physiological variations in the state of muscle fiber membranes." Basmajian&DeLuca: Muscles Alive

                                           Figure 1. Example of the EMG signal

    Besides basic physiological and biomechanical studies, kinesiological EMG is established as an evaluation tool for applied research, physiotherapy/rehabilitation, sports training and interactions of the human body to industrial products and work conditions.

    Typical benefits are:
    • EMG allows to directly “look” into the muscle
    • It allows measurement of muscular performance
    • Documents treatment and training regimes
    • Helps patients to “find” and train their muscles
    • Allows analysis to improve sports activities

    Based on these basic aspects, it is of vital importance to include a low cost sensor to achieve the acquisition of EMG signals on the Publys platform. There are various hardware implementations to acquire EMG signals, but mostly they use operational amplifiers with dual power supply.
    Since one of the premises of Publys is to build a device that uses a 3.7V battery, I must use integrated circuits that only need a single power supply, so I opted to use the AD8232 to build the EMG sensor.

    The EMG signal can be obtained from the motor units of the arm muscles using ordinary EMG surface electrodes. However, the raw EMG signal can not be used immediately, it needs to be processed, it must go through several procedures . To achieve this and deliver a signal that allows at least the movement of a 3D printed prosthetic hand, choose use the AD8232.

    Originally, this integrated circuit is designed for the acquisition of ECG (electrocardiograph) signals and heart rate monitoring. By changing certain components, as will be explained later, this circuit can be used in the acquisition of EMG signal since it shows a high degree of signal extraction, amplification and filtration in noisy conditions, which is the main problem of EMG signals. The internal configuration of AD8232 that aids in the process of signal processing is shown in Figure 2. However, the AD8232 can not provide enough filtration for the EMG by itself. For this reason, several passive components are connected to the chip in a way that makes the overall circuit more effective

                                            Figure 2. AD8232 inner configuration

    As can be seen in the internal configuration of the AD8232 we can identify some key elements such as: an instrumentation amplifier (IA), a operational amplifier (A1), a right leg drive amplifier (A2) and a reference buffer (A3).

    These are the inner connections of the AD8232 chip. The chip must be connected to certain components in order to enable it to perform the required task. The manufacturer suggests a configuration to extract ECG signals, this same configuration can be used to extract EMG signals, but the values of the components must be modified to have different cut-off frequencies than the ECG. Through the AD8232 filter design tool the values of the electronic components were obtained, the figures below show the frequency response.

                                         Figure 3. Gain in V for EMG signal in AD8232

                                 ...

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  • Biosensing for the human body

    Ever04/02/2018 at 20:28 0 comments

    Then proceed to explain each of the modules responsible for acquiring the different bioelectric signals to be sensed.

    Sensor 1: ECG

    “The ECG signal is one of the most important biosignals that can provide a great amount of information in medical and fitness applications. It senses the electrical activity of the heart during its muscular contractions. During the heartbeat, the muscular cells on the hearth surface depolarize their membrane. The resulting potential differences can be detected using surface electrodes placed in a proper configuration and a low noise signal amplifier. The typical frequencies of ECG signals go from 0.01 to 250 Hz and the amplitude is lower than 5 mV” (S.Benatti, B.Milosevic, M.Tomasini, E.Farella, P.Schonle, P.Bunjaku3, G.Rovere, S.Fateh, Q.Huang, L.Benini)

    There are multiple ways to acquire an ECG signal, for this device choose to use the AD8232 chip which has great advantages and can also be powered with a voltage of 3.3V.

    The AD8232, from Analog Devices, is a conditioning IC for applications of ECG measurements and other biopotentials. It is designed to extract, amplify and filter the small bioelectric signals in the presence of conditions of noise.

    The AD8232 has the ability to implement both a high-pass filter of two poles, as well as a three-pole low-pass filter for the elimination of noises; for this it has internal amplifiers elements attached to the architecture of the instrumentation amplifier. Also, to improve the CMRR, it has a special amplifier for the reference measurement (right leg).

    Some technical characteristics of the AD8232 are:

    • Supply voltage: 3.3 VDC
    • CMRR of the instrumentation amplifier: 80dB
    • Gain of the Instrumentation Amplifier: 100
    • Input impedance in differential mode: 10GΩ
    • Operating temperature range: [-40, 85] ° C
    • It has a spectral noise density of 100nV for F = 1KHz, 12uV for F = 0.1Hz at 10Hz, 14uV for F = 0.5Hz at 40Hz and a differential voltage of up to 300mV.

                                                        Figure 1. Functional block diagram.

    The acquisition of the ECG signal is essential to diagnose abnormalities cardiac. The electrical signal of the heart has very strong characteristics and an accurate acquisition system covering all the peculiarities of the ECG signal should be designed.
    The first is that the ECG frequency is between 0.05 and 100 Hz, sometimes up to 1KHz. Since the signal is very weak (approximately 1 mV peak-to-peak), it must be amplified. Besides, the instrumentation must have a high capacity to reject common mode (CMRR), normally in the range of 80 to 120 dB. To prevent small ECG signals are loaded on the skin, the ECG must have at least 10 MΩ impedance entry (Webster, Volume 3, 2006, 40-41).

    Design Implementation:

    The circuit for the acquisition, digitalization and transmission by Bluetooth of the signal consists of 3 electrodes connected to an analog front-end, this will filter and amplify the signal, a 12-bit ADC (ADS1015) and the Atmega328P that takes the signal coming from the ADC and it processes it through a set of algorithms. The communication between the board and a PC will be given thanks to the bluetooth that must be incorporated into the platform.

    The AD8232 passes the signals to Atmega328P which then processes it and displays the RT waveform on the PC display.

    The instrumentation amplifier that incorporates the AD8232, has a CMRR of 80 dB for a frequency range between 0 and 60 Hz (which, therefore, includes the line frequency). The input impedance is 10 G. The typical polarization currents are 50 pA, and the input offset current is 25 pA. The internal gain of the amplifier is 100.

    Within...

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Anthony Hernández wrote 4 days ago point

It´s a great project.

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Ever wrote 3 days ago point

Thanks Antony

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Ever wrote 04/01/2018 at 15:31 point

Thank you very much for your comment @zakqwy. I have reviewed both pages, but not in depth. For the moment I have focused on my experience in the development of portable medical devices that I have had in a year. Especially I have dedicated myself to working with the AD8232 and it offers great advantages to capture bioelectric signals, it consumes little current and can be used with a battery.
I still have a lot to document, but this week I will be updating the project and explaining all its basic fundamentals.

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zakqwy wrote 04/01/2018 at 13:36 point

Neat project! If you haven't already, be sure to check out the work of OpenBCI and Backyard Brains. Both companies have spent the last few years building open-source biosensing devices designed primarily for the education market.

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