pressure sensor

Discussion in 'Programmer's Corner' started by musica07, May 28, 2008.

  1. musica07

    Thread Starter Member

    May 28, 2008
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    hey. i'm currently doing a project related to measuring blood pressure using the pic18f2620. any idea of the program codes to sense the blood pressure of the person and how to capture the reading? any help will do. thx:)
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    What kind of hardware is going to sense the blood pressure? This will all be external to the PIC.
     
  3. Caveman

    Active Member

    Apr 15, 2008
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  4. musica07

    Thread Starter Member

    May 28, 2008
    13
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    we are doing by the oscillometric method. There will be a pressure sensor device attached to the cuff which will measure the bp of the ppl. i dont really know how to start the c program codes...any idea?
     
  5. Caveman

    Active Member

    Apr 15, 2008
    471
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    Start at main().

    Just kidding. You need to download example code and read it to understand how to start an embedded program. Any basic embedded program will give you the general idea of how to start. Many of microchip's application notes include source code. Try there first.
     
  6. musica07

    Thread Starter Member

    May 28, 2008
    13
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    thx! i'll give a try first:)
     
  7. musica07

    Thread Starter Member

    May 28, 2008
    13
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    I have already did the main program codes but i am still not sure on how to do the codes for the pressure sensor part. How do i invent c codes to capture the user's blood pressure reading? Can i use void PSENSOR(void) function call? I am really stuck at this part. Any ideas? Thanks!
     
  8. RiJoRI

    Well-Known Member

    Aug 15, 2007
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    As beenthere said, what's the sensor hardware interface? That is, does it provide a voltage level? And if so, what is the range? Does it give a digital output? If so, what is the means of extracting the information? Does it give a PWM output? That is, the on-time of the data is relative to the pressure? And if so, how should the various pulse widths be interpreted?

    Without knowing at least this information, neither you nor we can go any further.

    --Rich
     
  9. musica07

    Thread Starter Member

    May 28, 2008
    13
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    The device includes an electric air pump which drives at 6V. It will pump out air to the pinch valve. Air will then flow to the pressure sensor and finally the cuff. There will be an exhaust air outlet in between the pressure sensor and the cuff.

    During the inflation period, the motor will be activated and the pinch valve will be opened so that air can pass through it and then enters the pressure sensor. The exhaust air outlet will be closed so that air flowing out from the pressure sensor will directly enter the cuff. The pressure sensor will start measuring the bp and at a certain point, there will be some oscillations which will be captured. This is the systolic pressure.

    When the pressure sensor reaches the maximum pressure(eg:200mmHg), air will flow out from the cuff and escape through the exhaust air outlet. Pinch valve will be closed. As the cuff starts to deflate(air escapes thru the air outlet), there will be some oscillations occuring which will be captured. This is the diastolic pressure.

    I have to come out with some c codes for the bp process and capture the systolic and diastolic pressures. The main program which includes the lcd, buzzer, leds and switches are done so i'm left with this part which i'm stuck at.

    Can i use void PSENSOR(void)? Or do i use void INIT_BP(void), int CAPTURE_BP(void), void STOP_CAPTURING_BP(void)? Must i have this: #include <bp.h> ?

    I am not vey good at progamming so any help will be greatly appreciated. Thanks!!!:)
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    We still have no description of the hardware involved with sensing the oscillations. Or the nature if the electrical output that your microprocessor will be looking at. Without a proper interface for every device, no amount of programming will accomplish anything.
     
  11. carrie_

    New Member

    Jun 12, 2008
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    hello, just wanted to drop by to say that i'm building the blood pressure sensor too. i'd go into details, but maybe lets keep in touch? drop me a PM, if you like.

    :) cheers,
    Carrie
     
  12. musica07

    Thread Starter Member

    May 28, 2008
    13
    0
    The oscillometric method was used. The motor will pump out air into the cuff until the pressure reaches to about 180mmHg. When it reaches the max pressure(180mmHg), the motor will stop pumping and the air will slowly escape from the cuff(deflate). The pressure in the cuff will start to decrease. As the cuff starts to deflate, tiny oscillations in the air pressure of the cuff will be measured. The systolic pressure is when the pulsation occurs. A while later, the pressure in the cuff will decrease further. The diastolic pressure is when the oscillations starts to disappear.

    The pressure transducer used to sense the pressure from the cuff consists of an analog circuit which includes two TLV274(Op-Amp), a potentiometer and a few resistors. It drives at 3V. It is used to amplify both the DC and AC components of the output signal of the pressure transducer. The pressure transducer produces the output voltage proportional to the appied differential input pressure.

    Does this help? I am not so sure on how to get the blood pressure readings. Any help is greatly appreciated:)
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
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    Do you have any idea of the magnitude of the signals out of the circuit? Can you post up a schematic of the transducer circuit? What use is the DC component?
     
  14. Arm_n_Legs

    Active Member

    Mar 7, 2007
    183
    10
    Interesting project !! I would like a glimpse of your hardware.

    Your pressure sensor basically measures the pressure of the air in the cuff. Base on two specific points of oscillation which represent the diastolic and systolic blood pressure, you take the value from the pressure sensors. The main issues are the signal that is representing this oscillation and the pressure values.

    The fastest way to develop is to use an OEM blood pressure measurement kit.
    http://www.corscience.de/en/medical-engineering/oem-solutions/oem-modules/blood-pressure-measurement-oem-module-nibp2010-5v-12v.html.

    These devices communicates with the host (PC or microcontroller) via RS232C. Host initiate start of measurement. The device will send diasytolic and systolic reading through the RS232C.
     
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