Samsung S3P8245 User Manual

S3P8245

ARM Blood Pressure Monitor

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Revision 0.00

July 2010

Important Notice

The information in this publication has been carefully checked and is believed to be entirely accurate at the time of publication. Samsung assumes no responsibility, however, for possible errors or omissions, or for any consequences resulting from the use of the information contained herein.

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"Typical" parameters can and do vary in different applications. All operating parameters, including "Typicals" must be validated for each customer application by the customer's technical experts.

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Samsung Electronics Co., Ltd. San #24 Nongseo-Dong, Giheung-Gu Yongin-City, Gyeonggi-Do, Korea 446-711

TEL: (82)-(31)-209-3865 FAX: (82)-(31)-209-6494

Home Page: http://www.samsungsemi.com

Revision History

Revision No. Date Description Author(s)

0.00 June 17, 2010 - Initial draft Xu Hui

Table of Contents

1 OVERVIEW OF ARM BLOOD PRESSURE MONITOR...................................8

1.1 KEY Features of ARM Blood Pressure Monitor...........................................................................................9

1.2 System Block Diagram...............................................................................................................................10

1.3 Principles of Electronic Blood Pressure Monitor........................................................................................10

1.4 Process of Blood Measurement in Blood Pressure Monitor ......................................................................11

2 HARDWARE IMPLEMENTATION.................................................................13

2.1 Analog Signal Processing ..........................................................................................................................13

2.1.1 Introduction to MPS-3117 Pressure Sensor.......................................................................................14

2.1.2 Constant Current Driver Circuit ..........................................................................................................14

2.1.3 Differential amplifier circuit .................................................................................................................15

2.1.4 High Pass Filter Circult: 0.8Hz............................................................................................................16

2.1.5 Amplifier Circuit: 11x...........................................................................................................................17

2.1.6 Low-Pass Filter Circuit: 38Hz .............................................................................................................18

2.1.7 Pulse Rate Trigger Circuit ..................................................................................................................19

2.1.8 Interface between Analog Board and Main Board..............................................................................20

2.2 Microcontroller............................................................................................................................................21

2.2.1 Key Features of S3P8245 ..................................................................................................................22

2.2.2 Resource Assignment ........................................................................................................................23

2.2.3 LCD.....................................................................................................................................................24

2.2.4 Battery Voltage Detect........................................................................................................................24

2.2.5 I2C Device: EEPROM and Real Time Clock......................................................................................25

2.3 Pump Motor Driver Circuit..........................................................................................................................26

2.4 Valve Motor Driver circuit...........................................................................................................................27

2.5 Buzzer Enable and Driver Circuit...............................................................................................................28

2.6 Power Supply Circuit..................................................................................................................................29

3 SOFTWARE IMPLEMENTATION..................................................................30

3.1 Initialization ................................................................................................................................................31

3.2 Battery Voltage Detect ...............................................................................................................................31

3.3 Blood Pressure Monitor .............................................................................................................................33

3.3.1 Overview of Blood Pressure Monitor ..................................................................................................33

3.3.2 Monitor DC and AC Signals of Blood Pressure..................................................................................35

3.3.3 Analysis ..............................................................................................................................................36

3.4 EEPROM Write and Read Operations.......................................................................................................37

3.5 Interrupt Service Subroutine ......................................................................................................................38

3.5.1 Pulse Rate Input ISR ..........................................................................................................................38

3.5.2 User Button (Power On/Off) ISR ........................................................................................................39

3.5.3 User Button (Start, Up/Down, Delete, Save) ISR ...............................................................................40

4 SCHEMATIC ..................................................................................................42

5 PCB LAYOUT ................................................................................................44

6 MEASUREMENT............................................................................................48

6.1 Test Environment.......................................................................................................................................48

6.2 Final Measurement Environment Setting...................................................................................................49

6.3 Test Result .................................................................................................................................................50

7 APPENDIX 1: BILL OF MATERIALS ............................................................51

8 APPENDIX 2: SOURCE CODE......................................................................54

List of Figures

Figure Title Page Number Number

Figure 1-1 Types of Blood Pressure Equipments ..................................................................................................9

Figure 1-2 System Block Diagram .......................................................................................................................10

Figure 1-3 DC and AC Components of Blood Pressure Signal and SBP/DBP Position......................................12

Figure 2-1 Analog Board (Driver, Diff-amp, 0.8Hz HPF, 11x Amp, 38Hz LPF, and Comparator) Circuit............13

Figure 2-2 MPS-3117 Pressure Sensor Appearance and Pin Assignment .........................................................14

Figure 2-3 Constant Current Driver and Pressure Sensor...................................................................................14

Figure 2-4 Diff-amplifier Circuit ............................................................................................................................15

Figure 2-5 High Pass Filter Circuit : 0.8Hz...........................................................................................................16

Figure 2-6 Amplifier Circuit : 11x..........................................................................................................................17

Figure 2-7 Low-Pass Filter Circuit : 38Hz ............................................................................................................18

Figure 2-8 Pulse Rate Trigger Circuit...................................................................................................................19

Figure 2-9 Interface between Analog Board and Main Board..............................................................................20

Figure 2-10 Microcontroller Circuit .......................................................................................................................21

Figure 2-11 LCD Function Diagram and External Driving Circuit ........................................................................24

Figure 2-12 Battery Voltage Detect Circuit...........................................................................................................24

Figure 2-13 EEPROM Circuit and Real-time Clock Circuit ..................................................................................25

Figure 2-14 Pump Motor Driver Circuit ................................................................................................................26

Figure 2-15 Valve Motor Driver Circuit.................................................................................................................27

Figure 2-16 Buzzer Enable and Driver Circuit......................................................................................................28

Figure 2-17 Power Supply Circuit ........................................................................................................................29

Figure 3-1 System Flow Chart .............................................................................................................................30

Figure 3-2 Battery Voltage Detect Flow Chart .....................................................................................................32

Figure 3-3 Blood Pressure Monitor Flow Chart....................................................................................................34

Figure 3-4 Monitor DC and AC of BP Flow Chart ................................................................................................35

Figure 3-5 Analysis Flow Chart ............................................................................................................................36

Figure 3-6 EEPROM Write and Read Operation Flow Chart...............................................................................37

Figure 3-7 Pulse Rate Input (External INT0) ISR Flow Chart ..............................................................................38

Figure 3-8 User Button (Power ON/OFF, External INT2) ISR Flow Chart...........................................................39

Figure 3-9 User Button (Start, Up/Down, Delete, Unit, Save, External INT4-7) ISR Flow Chart.........................41

Figure 4-1 Schematic of Analog Board ................................................................................................................42

Figure 4-2 Schematic of Main Board....................................................................................................................43

Figure 5-1 Main Board and Analog Board PCB Assembly (Top Layer)...............................................................44

Figure 5-2 Main Board and Analog Board PCB Assembly (Bottom Layer) .........................................................45

Figure 5-3 Main Board and Analog Board PCB (Top Layer) ...............................................................................45

Figure 5-4 Main Board PCB (Bottom Layer) ........................................................................................................46

Figure 5-5 Final Implementation of Blood Pressure Monitor (Main Board)..........................................................47

Figure 5-6 Final Implementation of Blood Pressure Monitor (Analog Board) ......................................................47

Figure 6-1 Final Measurement Environment Setting ...........................................................................................49

Figure 6-2 Blood Pressure Signals Measurement Waveform..............................................................................50

List of Tables

Table Title Page Number Number

Table 2-1 Microcontroller Resource Assignment .................................................................................................23

Table 7-1 Bill of Main Board Materials .................................................................................................................51

Table 7-2 Bill of Analog Board Materials..............................................................................................................53

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1 OVERVIEW OF ARM BLOOD PRESSURE

MONITOR

This application note describes an arm blood pressure monitor (BPM) based on Samsung's S3P8245 microcontroller. The reference design is intended for novices, who are not familiar with blood pressure monitor system design. You can modify the design to build more complicated applications.

With rising living standards and increase in ageing among people, medical testing equipments have become necessity for families. For instance, home blood pressure equipments have become increasingly popular with the Chinese families.

Usually, these equipments are of two types:

• First is the Mercury sphygmomanometer. The main advantage of such equipment lies in its numerical stability.

However, the disadvantages include: patients cannot measure themselves if they are alone; the equipment must be operated by healthcare professionals. This equipment can also result in significant visual observation error. The measurement results can be different, depending on the doctor's experience and criterion, so it can lead to subjectivity. The Mercury sphygmomanometer is bulky and not easy to carry (not portable).

• Second is the electronic Blood Pressure Monitor (BPM). The main advantage of such equipment include: ease of use; patients without any professional training can also use this equipment. It is easy to record the measured values with this equipment. Besides, it is lightweight and portable. Due to its advantages, more families are using this equipment. From 2007 to 2010 alone, China's annual demand for electronic blood pressure monitor grew to 350 million units.

Electronic blood pressure monitor are of two types:

• Wrist blood pressure monitor

• Arm blood pressure monitor

S3P8245_ARM BLOOD PRESSURE MONITOR_AN_REV 0.00 错误！未定义样式。错误！未定义样式。

Figure 1-1 shows all the above-mentioned blood pressure equipments.

a. Mercury Sphygmomanometer b. Wrist Blood Pressure Monitor c. Arm Blood Pressure Monitor

Figure 1-1 Types of Blood Pressure Equipments

1.1 KEY Features of ARM Blood Pressure Monitor

The key features of arm blood pressure monitor based on Samsung's S3P8245 microcontroller include:

• Measurement: Arm-type

• Measuring range: Pressure: 0 ~ 299mmHg (0 ~ 39.9kPa), Pulse: 40 ~ 180 beats/minute

• Accuracy: Pressure: ±4mmHg (±0.5kPa), Pulse: ±5%

• Pump method: Inflatable pump automatic inflate

• Deflate method: Release valve automatic deflate

• Measurement method: Oscillographic determination method

• Functions:

− User button: Power On/Off, Start, Up/Down, Delete, Save, and Unit

− Records up to 35 blood pressure monitoring records

− No user button operation; automatic shutdown after 30 seconds

• Power: 4x AA batteries or 6V DC power supply

• Battery life: 200 times measurement

• Operation temperature and humidity: +10℃ ~ +40℃; 30%RH ~ 85%RH

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1.2 System Block Diagram

Note of BPM System Block

BT +6V : Battery +6 V Power Mana. : Power Management

Cons. Cur. Driver : Constant Current Driver

Start But. : User Button Power But. : User Button RTC :

Real Timer Clock

: Not used

Cons. Cur .

Driver

2nd Order HPF : 0 .8Hz

Amplifier

11 x

(Start)

(Power ON/OFF)

10 MHz

32. 768 KHz

Battery Vol . CPU

Pressure

Sensor

V+ V-

Diff - Amp

Analog Board V 1 . 0

2 nd Order

LPF : 38Hz

ADC2

ADC0

ADC1

+6V

OSC

ADC

INT0

Pulse Rate

Trigger

Power Mana .

+5V

S3P8245

ROM

SIO

RAM

Ext. INT

INT1 INT2

Start

But .

EEPROM

I/OPWR

LCD

BUZ

INT4-INT7

Power

But .

Main Board V 2 .1

RTC

19 SEG * 4 COM

Other

User Button

LCD Screen

Pump

Motor

Valve

Motor

Figure 1-2 System Block Diagram

1.3 Principles of Electronic Blood Pressure Monitor

Typically, blood pressure can be described as systolic blood pressure (SBP) and diastolic blood pressure (DBP).

• Systolic blood pressure (SBP): The blood pressure is measured at the time of heart contraction, that is, when blood hits the blood vessels.

• Diastolic blood pressure (DBP): The blood pressure is measured when the heart does not contract. If the cuff pressure is equal to the blood pressure, blood begins to flow and produces a "cuff" sound. The blood pressure is measured at this point (SBP). Once the cuff sound weakens, it gradually disappears. The blood pressure is measured again at this point (DBP).

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1.4 Process of Blood Measurement in Blood Pressure Monitor

• The process of blood pressure measurement in the blood pressure monitor is described as follows:

• When the patient presses the Start button, the microcontroller opens the inflatable pump motor.

• The BPM system inflates up to 200mmHg. After reaching this value, it slowly deflates with the speed of

5mmHg per second.

• The pressure sensor outputs a signal through differential amplifier.

− One part of signal goes to the ADC0 channel to monitor the DC component of blood pressure signal.

− Other part goes to 0.8Hz second order high-pass filter to remove the DC component.

− Rest of the AC component of 11x amplification is inputted to the 38Hz second order low-pass filter (to filter

power and skin friction with the cuff of high-frequency noise and frequency interference, and to adjust the signal in the range of 0 to 5V).

− One part of the filtered AC signal is sent to the pulse rate trigger circuit for generating trigger pulses that

starts the ADC module operation.

− Other part is sent to the ADC1 channel for calculating the amplitude of AC signal.

• Find the maximum peak-to-peak amplitude. Mark this point as MAP point.

• Before MAP point, determine the value that is the closest to 0.54*MAP. The corresponding DC component

value of this transient position specifies the systolic blood pressure (SBP) value.

• After MAP point, determine the point whose value is closest to 0.72*MAP. The corresponding DC component value specifies the diastolic blood pressure (DBP) value.

• By using the internal timer to measure the interval between every two adjacent pulses, the system easily obtains the pulse rate (PR) value.

• All the measurement results will be showed on the LCD screen.

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Figure 1-3 shows the system operation process, blood pressure, systolic and diastolic blood pressure signals, and

their position.

Pump Deflate

DC . BP

MAP

DBP

SBP

AC . BP

Figure 1-3 DC and AC Components of Blood Pressure Signal and SBP/DBP Position

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2 HARDWARE IMPLEMENTATION

2.1 Analog Signal Processing

The blood pressure monitor system needs a filter and an amplify circuit for the purpose of processing weak analog signals and recognizing pulse signals. Such system is made of a single PCB board called the Analog Board. The board provides a constant current driver (for pressure sensor), pre-amplifier (for pressure sensor's output weak signal), high-pass filter, intermediate amplifier, low-pass filter, and pulse signal (which is sent to the MCU).

Figure 2-1

4.7K ohm

P1.2/T1PWM

VHPF

shows a schematic diagram of the Analog Board.

VCC_+5V

4.7K ohm

Q1 9012

1 2 3

CON3

Amplifier: 11x

U4A LM358

VCC_+5V

8 4

R28 10K ohm 1%R27 1K ohm 1%

1.2K ohm

MPS-3117-006G_6_SOP

Pressure Sensor

VMAG

C13 104

R31 49.9K ohm 1%

R5 0 ohm

AGND

R11 30K ohm 1%

R12 30K ohm 1%

R32 10K ohm 1%

GND

R6 1M ohm 1%

R20

2.4K ohm

AC Signal of BP

104

R29 30K ohm 1%

2nd Order LPF: 38Hz

R13 1M ohm 1%

R16

1.3M ohm 1%

VCC_+5V

R21

182K ohm

P2.1/ADC1

C11 104

R7 1.3M ohm 1%

U2A LM358

VCC_+5V

8 4

C4 104

C5 104

8 4

VDIF F

R23 100 ohm 1%

C6 10uF

R30 1K ohm 1%R25 1K ohm 1 %

LM358 U4B

VCC_+5V

R35 1M ohm 1%

R3 100 ohm 1%

104

P2.0/ADC0

104 R14 1K ohm 1%

R17 1M ohm 1% R18 1.5M ohm 1% R19 360K ohm 1%

C7 104

VLPF

104

R33 5. 1M ohm 1%

DC Signal of Blood Pressure (BP)

C1 10uF

VCC_+5V

R8 1M ohm 1%

VCC_+5V

R34 10M ohm 1%

R22

100K ohm 1%

R24

50K ohm

VCC_+5V

R9 200K ohm 1%

U2B LM358

R15 1K ohm 1%

2nd Order HPF: 0.8Hz

Pulse Rate Detector

641

LM311

C12 104

R10 200K ohm 1%

VHPF

VCC_+5V

R26

10K ohm

P0.0/INT0

C10

Pulse Rate

104

Figure 2-1 Analog Board (Driver, Diff-amp, 0.8Hz HPF, 11x Amp, 38Hz LPF, and Comparator)

Circuit

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2.1.1 Introduction to MPS-3117 Pressure Sensor

MPS-3117 is a pressure sensor for blood pressure monitor from Taiwan Metrodyne Microsystem Corp. Its dimension is 7mm×7mm×10mm, and its measurable pressure ranges from -299.95mmHg to +299.95mmHg. MPS-3117 uses a constant source to drive the Wien Bridge. It sends the double-ended output differential signals according to the pressure.

Figure 2-2

shows the appearance and pin assignment of MPS-3117 pressure sensor.

Figure 2-2 MPS-3117 Pressure Sensor Appearance and Pin Assignment

2.1.2 Constant Current Driver Circuit

The BPM system requires a constant current source to drive pressure sensor. The typical value of drive current is 1mA while the maximum value of drive current is 3mA.

VCC_+5V

1 2 3

CON3

4.7K ohm

Q1 9012

1.2K ohm

MPS-3117-006G_6_SOP

4.7K ohm

P1.2/T1PWM

Figure 2-3 Constant Current Driver and Pressure Sensor

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2.1.3 Differential amplifier circuit

In the BPM system, the differential amplifier plays the role of amplifying weak signal output from pressure sensor. One way to do that is directly to the microcontroller as a DC signal of blood pressure. The other signal is provided to the back analog circuits for filtering and amplification processing.

The diff-amplifier circuit output can be calculates as follows:

VVV VVVV

( ) ( ) ( ) ( ) 76.667 ( )

=×−= ×−≈×−

DIFF IN IN IN IN IN IN

+− +− +−

11.3

R7 1.3M ohm 1%

U2A

LM358

VCC_+5V

8 4

VCC_+5V

C4 104

C5 104

VDI FFVDI FF

R11 30K ohm 1%

R12 30K ohm 1%

R20

2.4K ohm

R6 1M ohm 1%

R13 1M ohm 1%

R16

1.3M ohm 1%

R21

182K ohm

Figure 2-4 Diff-amplifier Circuit

R3 100 ohm 1%

P2.0/ADC0

C1 10uF

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2.1.4 High Pass Filter Circult: 0.8Hz

The analog board of the BPM system uses 2nd order Butterworth high-pass filter circuit, whose transfer function is calculated as follows:

()

HPF

()

()()( )

8 9 10 2 3 8 9 10 17 18 19 2 3

R R CC R R R R R R CC

++ ++ + +

VCC_+5V

U2B LM358

R15 1K ohm 1%R14 1K ohm 1%

VHPF

VDI FF

R8 1M ohm 1% R 9 200K ohm 1% R10 200K ohm 1%

104

R17 1M ohm 1% R18 1.5M ohm 1% R19 360K ohm 1%

Figure 2-5 High Pass Filter Circuit : 0.8Hz

Suppose the network coefficient a11 of 2nd order Butterworth is 1.414 and the angular frequency is 0.8x2π, while the value of both C2 and C3 is 0.1uF. So, the values of R8+R9+R10 and R17+R18+R19 can be calculated as follows:

RR M

++ = = = Ω

8910

αω π

2311

0.1 0.1 1.414 0.8 2

0.1 0.1

×× ××

1.41

RR M

++= = = Ω

17 18 19

( ) 1.41 0.1 0.1 (0.8 2 )

RRRCC M

++ Ω××× ×

891023

ωπ

2.86

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2.1.5 Amplifier Circuit: 11x

The signal coming from high-pass filter is weak and needs to amplify. Therefore, the system uses an 11x magnification amplifier circuit.

R28 10K ohm 1%R27 1K ohm 1%

U4A

VHPF

8 4

LM358

VCC_+5V

C13 104

VMAG

Figure 2-6 Amplifier Circuit : 11x

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