Electrode Theory

        An interface is necessary between the body and the electronic measuring device when recording potentials and currents in the body.  Biopotential electrodes produce small voltages directly related to the changing electric field produced by a beating heart..  The Ag/AgCl electrode is a practical electrode that approaches the characteristics of a perfectly nonpolarizable electrode.  Perfectly nonpolarizable refers to the freedom of ions to pass through the electrode-electrolyte interface to be transduced into an electrical current.  The electrode converts the ionic current produced by the body into a voltage, and the ECG amplifies this voltage.  

The electrode-electrolyte interface is the junction where the ionic transfer occurs.  A temporary current is induced in the electrode from the changing electric field of the beating heart.  This current causes electrons and anions to move across the electrode-electrolyte interface in the direction opposite to the flow of the current, and for cations to migrate across this interface in the direction of the current.  This temporary separation of charge produces a temporary potential.  This potential is created from a current induced from the heart and is thus directly related to the changing electric field produced by a beating heart.  The ECG circuit hugely amplifies the potential, and the output gives the electric characteristics of a beating heart. 

Another sensor that was considered was the piezoelectric sensor.  Piezoelectric materials generate an electric potential when mechanically strained.  During a heart beat, the pressure in the blood vessels is higher than when the heart is in its resting stage.  This higher blood pressure causes a physical deformation in the skin, and thus a piezoelectric sensor can produce an electic potential during every heartbeat.  The principal reason why the piezeoelectric sensor is less than ideal is that it is pressure sensitive.  In order to pick up a signal the nurse or doctor would have to press the sensor hard against the patient which could cause a permanent deformation of the piezoelectric material  This information, combined with the fact that hospitals across the nation use Silver/Silver Chloride sensors,  made it obvious that the silver-silver chloride sensors were the best to use for this project.  :)

ECG Instrumentation


In order to record the ECG, we need a transducer capable of converting the ionic potentials
generated within the body into electronic potentials which can be measured by conventional
electronic instrumentation. Such a transducer consists of a pair of electrodes, which measure
the ionic potential difference between their respective points of application on the body
surface. Electrodes may be classified either as polarisable, in which case they behave as
capacitors, or non−polarisable, in which case they behave as resistors. Common electrodes
have characteristics that lie between these extremes; the silver−silver chloride electrode
discussed below approximates more closely to a non−polarisable electrode.


Electrode placement
The most obvious way to record the ECG is between the Right Arm (RA) and the Left Arm
(LA) although another two combinations using the Left Leg (LL) are also used clinically
(RA−LL and LA−LL).

Another electrode is also used to connect the patient to the common ground of the
instrumentation. Usually, this ground electrode is attached to the right leg.



Silver−silver chloride electrode
Electrodes for recording biopotentials are composed of a metal (usually silver for ECG
measurement), and a salt of the metal (usually silver chloride). In addition, some form of
electrode paste or jelly is applied between the electrode (normally a flat silver disc) and the
skin. The combination of the ionic electrode paste and the silver metal of the electrode forms
a local solution of the metal in the paste at the electrode−skin interface (also referred to as
the electrode−tissue or electrode−electrolyte interface). Hence, some of the silver dissolves
into solution producing Ag+ ion


problem???


Movement artefact
If the electrode is moved with respect to the elctrolyte, this mechanically disturbs the
distribution of charge at the interface and results in a momentary change of the half−cell
potential until equilibrium can be re−established. If a pair of electrodes are in contact with
an electrolyte and one moves while the other remains stationary, a potential difference
appears between the two during this motion. This potential is referred to as moverment
artefact and can be a serious cause of interference in the measurement of ECG (or any other
biopotential).

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Objective :

• to detect heart beat using sensor(electrode)
• to apply the sensor that can read the beat when heart pumping the blood
• to detect any abnormal beat calculation 
• that can be related to any illness/disease 
• to study the symptom of any disease that related to heart beat
• to use Arduino and PIC as a controller
• to use LCD and seven segment as a display
• to apply warning beeper with LED flash
• to apply at critical monitoring and daily monitoring
• to store data retrieve

pulse!!!!

Heart beat measurement indicates the soundness of the human cardiovascular system. This project demonstrates a technique to measure the heart beat by sensing the change in blood volume in a finger artery while the heart is pumping the blood. 

*for this project this concept explain how the measurement should be done. this is an early idea to make the HB monitoring .