week 9 ~~

UV box

for this week, i decided to do the etching on the PCB board using UV . this is suggested by my friend as i failed to etching the 1st board last week.  using this UV etching the pcb would be more clean and easy to drill.

week 3 (part 2)


At the beginning of this week i already do some programming for the electrode connection with Arduino. yesterday i already receive the parcel for the electrodes. ^_^

so the electrode is connect to the arduino input... and the programmed that made earlier is tested. unfortunately, it is not going well. maybe my electrode circuit has to re - construct.


so i'd tested the previous circuit at the lab again, hopefully i get to solve this problem.

week 3 ~~~~

for this week ,i'm doing my programming. i've doing some research on the programming on my semester break. I found that i'm more comfortable with Arduino microcontroller. So, i 'll proceed this project by using Arduino programming which is also in C language.

this programed above actually cannot be tested yet as the electrodes still not receive . 

Week 2 ~~

I'm still waiting for the electrodes. but to keep my work on schedule , i proceed on making the amp.

for this project the amp used to amplify the signal that read from the heart by placing electrodes at the chest.

the amp work well , but 1 of the IC is faulty it doesn't give the same voltage as others IC has. It detected by measuring the IC legs one-by-one and then compare to others IC( same IC).

The making~~~~ ^_^

For the first week of 2013, i has been to Jalan Pasar ,Pudu for purchasing some components and also trying to search for the electrode or any sensor that proximate the same as the electrode .

but after 2days searching for the electrode and sensor, i'll didn't find any of them ..

so, after thinking , my friend suggest for me to search it online. I found this one website that selling the electrodes but in bulk. But after some discussion they agree to sell to me 2bags only. 1 bags cost me US$ 12. The shipping is a bout 2weeks. So i buy it on9 :) .......  

Microcontroller

An 8-bit microcontroller was chosen to process the output signal produced by the amplification stage. The Microchip PIC16F877A was selected due to its additional output and processing power, and also its onboard 10-bit analogue to digital converter and in-circuit debugging features. Using this highly integrated microcontroller allowed for a simpler design and trouble shooting debugging process. Due to the use of a microcontroller to calculate the beats per minute (BPM), it was decided that a liquid crystal display (LCD) module would be the most flexible way of displaying this numerical output. It was originally planned that several seven segment displays could be used, but again it was deemed worthwhile to integrate the display unit together and limit the number of components required. In addition, the information which the LCD could convey was greater. Below is a block diagram of the microcontroller and LCD process:

 

Regarding the actual BPM calculation (assuming that it was possible to translate each R part (the blip/spike peak) into singular events occurring in a timely fashion of course) it was originally going to be done by measuring the total number of spikes within a certain amount of time and then multiplying this count by a factor (as it is done when using a clock and your hand). With the use of the microcontroller however more precise measurements were able to be made resulting in an output of greater accuracy and speed.

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.  :)