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Human body sensing system

 

 

PROJECT DESCRIPTION

 

The project skin response monitor is a very useful project for medical field. This can be used to monitor the heartbeats in digital display format. The heart beat information available in digital format is easy to understand. In our heartbeat monitor project we have used two electrodes to sense the blood pumping done by heart which are proportional to heartbeats. The sensing electrode sense the blood pumping cycles and send the signal to current amplifier. We are using three stages of amplifiers to amplify weak signals sensed by sensing electrodes. The amplified signals are processes to extract the cycles of blood through our body. The average value of sensed cycles of blood pumps are displayed per minute interval. We have used microcontroller AT89S51 to process the sensed signal from sensor and displayed on 16x2 LCD display.

MEASUREMENT OF PHYSIOLOGICAL PARAMETER This -invention relates to a method and apparatus for the determination of arterial blood pressure. We have found that determination of the time interval between a heart beat and the associated arterial pulse is related, inter alia, to arterial blood pressure and hence may be used to provide a continuous, non-invasive method for the determination of arterial blood pressure.

Of the two common methods for determination of arterial blood pressure, one is non-invasive but discontinuous and the other is continuous but invasive. The non-invasive method uses a sphygmomanometer which comprises an inflatable rubber cuff connected to a mercury manometer. In use, the cuff is placed around the upper arm and inflated until blood flow in the brachial artery is occluded. A stethoscope is then used, as the pressure in the cuff is gradually reduced, to determine the systolic and diastolic measuring points. The pressure of each of these points is read from the manometer and quoted as the blood pressure. The technique is simple to operate and firmly established in general and clinical medical practice but is not particularly accurate and, since each measuring operation takes some

20-30 seconds to perform, is discontinuous.

_ The continuous method involves the surgical insertion of a catheter in the brachial artery. The catheter is connected to a suitable pressure transducer and this provides a direct, accurate and continuous determination of blood pressure. However, since the method is invasive, it is suitable for use only during relatively major surgery. According to the present invention, a method for the measurement of arterial blood pressure comprises sensing a heart beat, sensing an arterial pulse at at least one location and ascertaining the time interval between at least one heart beat and at least one associated arterial pulse.

The invention also includes apparatus for the measurement of arterial blood pressure, the apparatus comprising first sensing means for sensing a heart beat, second sensing means for sensing an arterial pulse at at least one location, and means for ascertaining the time interval between at least one heart beat and at least one associated arterial pulse.

The present invention, therefore, provides a continuous, non—invasive technique and the output of the apparatus according to the invention is representative, inter alia, either of dynamic

comparative blood pressure or, with suitable calibration, dynamic absolute blood pressure.

The heart beat sensing means may comprise a simple pressure transducer in contact with the chest but it is preferred for reasons of accuracy to utilise electrocardiography. In particular, we have found that the R wave of an electrocardiogram, which corresponds to the beginning of ventricular systole, is a convenient reference for measurement of cardioarterial dela .

The arterial pulse may be sensed at one or more locations, for example at the carotid or temporal arteries in the head and neck, at the brachial radial or ulnar arteries in the arm and wrist, and/or in the fingertip, groin and leg. Sensors which may be used include temperature sensitive devices, piezo-electric transducers, strain gauges, ultrasonic transducers and plethys ographic transducers. Ultrasonic transducers rely on the Doppler effect to detect movement in the arterial wall and/or the flow of blood corpuscles while plethysmographic transducers measure volume changes which result from arterial pulsatile blood flow. Volume changes may be detected by measurement of impedance changes or temperature changes but we prefer to use

- Λ - photoplethysmography, which is an optical technique. In photoplethysmography, light is transmitted into the tissues and the amount of light reflected is inversely proportional to the volume of blood present in the artery, thereby affording a means of detecting changes in volume of the artery with pulse. Conveniently, light in the near infra-red region (wavelength 700- lOOOnm) is used since such light has a relatively high transmittance through tissue but is scattered by blood. Δ light emitting diode which emits in the infra-red may be used as the source of light and a light-sensitive photo-transistor may be used to measure reflected light. An infra-red light emitting diode is particularly convenient because the degree of scattering of light of this wavelength is substantially Independent of the degree of oxygenation of the blood.

The time interval between heartbeats and associated arterial pulses may be ascertained using either an analogue or a digital approach. Preferably the time intervals are electronically processed to give information such as average and instantaneous values of blood pressure and/or to cause operative reactions in other equipment of a diagnostic or therapeutic nature, such as warning devices and the like.

The invention will now be described by way of example with reference to the accompanying drawings of which:

Fig. 1 is a block diagram illustrating the equipment and procedures to which subjects were subjected to determine a delay (Td) between heart beats and associated arterial pulses;

Fig. 2 is a block diagram showing an electrocardiograph system; Fig. 3 is a block diagram showning an arterial pulse transducer system;

Figs. 4.1 to 4.7 are plots of Td against average blood pressure for each of seven subjects. Referring first to Fig. 1, a subject under test was connected as shown to an electrocardiograph and to an arterial pulse transducer. In connecting the electrocardiograph, a standard application of bipolar recording was used in which three identical electrodes are attached one to each arm and one to the left leg of the subject. The two arm electrodes were conncted to the inputs of a differential amplifier, the leg one being connected to common.

As shown in Fig. 2, the differential output was fed to a band pass filter with an approximate 3dB bandwidth of 0.08-80 Hz. This filter was used to remove noise and unrelated spurious

signals. In order to reduce 50 Hz mains interference, the output of the band pass filter was fed to a 50 Hz notch filter. This provided some 20dB's of attenuation at 50 Hz. The output of the notch filter was differentiated for convenience to provide a signal based on the rate of change of the ECG. The ZERO crossings of the derived waveform indicate the peaks of the original ECG waveform. The arterial pulse transducer comprised a Texas Instruments' TIL 139 combined gallium arsenide IR-emitting diode/npn silicon phototransistor mounted together in a moulded ABS plastics housing and held against the finger to detect the arterial pulse therein. The emission from this device typically peaks at wavelength of 940nm. At this wavelength, variations in the optical density of the underlying tissue are primarily determined by the pressure pulse. As shown in Fig. 3, the output of the phototransistor was amplified and fed to a band pass filter and a notch filter similar to those described with reference to Fig. 2. The notch filter output was then fed via a variable non-inverting amplifier to a differentiating circuit identical to that used for the electrocardiograph signal.

The electrocardiograph (ECG) and arterial

pulse (AP) transducer differentiator circuits indicated the rate of change of the respective signals and thus of their peaks. The results were recorded on a Medelec UV recorder to allow manual measurement of the values of the time intervals Td.

In use, the subject under test was connected to the equipment as shown in Fig. 1. The arterial pulse signals were obtained by using the AP transducer to detect the subject's finger pulsations. The experiment was divided into three parts: i. Initially measurements were made of the systolic and diastolic arterial blood .pressure with the subject "at rest", using a sphygmomanometer . ii. A period of exercise was undertaken consisting of a short jogging session around a predetermined route, sufficient to raise the subject's blood pressure to a high value. iii. Periodic measurements of systolic and diastolic blood pressure were then made until the subject's blood pressure had returned to the "at rest" value measured in (i). The ECG and AP results were recorded simultaneously with the blood pressure measurements being taken. The Medelec UV recorder used for

the differentiated outputs is an instrument consisting of both an oscilloscope and UV trace recorder. Traces displayed on the oscilloscope screen can also be recorded on UV sensitive paper producing a permanent record of the waveform being displayed. The oscilloscope has four inputs, two of which are connected to ECG and AP differentiator outputs. The other two are calibrated to ground and positioned to be superimposed on the AP and ECG traces to provide a reference. This ground reference is used to determine the zero crossing that defines the peaks of the input waveforms.

A sufficient length of UV trace recording was done to capture six or more cardiac cycles for each sphygmomanometer measurement. On each UV trace, the subject's initials and blood pressure readings were also recorded. For each experiment on a particular subject a set of 7 or 8 UV trace recordings was obtained. The values of Td were measured, using a rule, from the differentiated zero crossing corresponding to the R wave peak of the ECG to the zero crossing corresponding to the first peak of the AP . Together with the blood pressure readings these were entered into a computer program to calculate: i. the individual values of Td in msecs

for each cardiac cycle; i_i . the average value of Td in msecs over each sphygmomanometer measurement; and ill. the average manually measured blood pressure in mm Hg.

Thus, for a given subject, a set of average Td values and a set of average blood pressure values measured manually by sphygmomanometer were derived. Typically, sets of 7 or 8 values were obtained.

These values were then plotted on to graphs of average Td vs average measured blood pressure, and were also used as input data to a linear regression program to test the degree of correlation. The graphs are shown in Figs. 6.1 to 6.7, each graph representing results for one subject. In the graphs, the straight line is derived from linear regression and the deviation of the plotted points for Td vs blood pressure gives an indication of the degree of correlation.

 

MICROCONTROLLER AT89C51

 

Architecture of 8051 family:-

 

                  

The figure – 1 above shows the basic architecture of 8051 family of microcontroller.

 

Features

• Compatible with MCS-51™ Products

• 4K Bytes of In-System Reprogrammable Flash Memory

– Endurance: 1,000 Write/Erase Cycles

• Fully Static Operation: 0 Hz to 24 MHz

• Three-Level Program Memory Lock

• 128 x 8-Bit Internal RAM

• 32 Programmable I/O Lines

• Two 16-Bit Timer/Counters

• Six Interrupt Sources

• Programmable Serial Channel

• Low Power Idle and Power Down Modes

 

Description

 

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes of Flash Programmable and Erasable Read Only Memory (PEROM). The device is manufactured using Atmel’s high density nonvolatile memory technology and is compatible with the industry standard MCS-51™ instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The AT89C51 provides the following standard features: 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, five vector two-level interrupt architecture, a full duplex serial port, and on-chip oscillator and clock circuitry.

In addition, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset.

 

Pin Description

 

VCC

Supply voltage.

 

GND

Ground.

 

Port 0

Port 0 is an 8-bit open drain bidirectional I/O port. As an output port each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs. Port 0 may also be configured to be the multiplexed low order address/data bus during accesses to external program and data memory. In this mode P0 has internal pull-ups. Port 0 also receives the code bytes during Flash programming, and outputs the code bytes during program verification.

External pull-ups are required during program verification.

 

Port 1

Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. Port 1 also receives the low-order address bytes during Flash programming and verification.

 

Port 2

Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this application it uses strong internal pull-ups when emitting 1s. During accesses to external data memory that uses 8-bit addresses (MOVX @ RI); Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order address bits and some control signals during Flash programming and verification.

 

Port 3

Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull-ups. Port 3 also serves the functions of various special features of the AT89C51 as listed below:

Port 3 also receives some control signals for Flash programming and verification.

 

RST

Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.

 

ALE/PROG

Address Latch Enable output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.

 

PSEN

Program Store Enable is the read strobe to external program memory.

 

Port Pin Alternate Functions

P3.0 RXD (serial input port)

P3.1 TXD (serial output port)

P3.2 INT0 (external interrupt 0)

P3.3 INT1 (external interrupt 1)

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input)

P3.6 WR (external data memory write strobe)

P3.7 RD (external data memory read strobe)

 

When the AT89C51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.

 

EA/VPP

External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal program executions. This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming, for parts that require 12-volt VPP.

 

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

 

XTAL2

Output from the inverting oscillator amplifier.

 

Oscillator Characteristics

XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 2.There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be observed.

 

Idle Mode

In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled

Interrupt or by hardware reset. It should be noted that when idle is terminated by a hard

Hardware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal reset algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To

Function: Jump if bit is set

Description: If the indicated bit is a one, jump to the address indicated; otherwise proceed with the next instruction. The branch destination is computed by adding the signed relative-displacement in the third instruction byte to the PC, after incrementing the PC to the first byte of the next instruction. The bit tested is not modified. No flags are affected.

Example: The data present at input port 1 is 11001010B. The accumulator holds 56

(01010110B). The instruction sequence

JB P1.2, LABEL1

JB ACC.2, LABEL2

will cause program execution to branch to the instruction at label LABEL2.

Operation: JB

(PC) ¬ (PC) + 3

if (bit) = 1

then (PC) ¬ (PC) + rel

Bytes: 3

Cycles: 2

Encoding: 0 0 1 0 0 0 0 0 bit address rel. address

 

JBC bit, rel

Function: Jump if bit is set and clear bit

Description: If the indicated bit is one, branch to the address indicated; otherwise proceed with the next instruction. In either case, clear the designated bit. The branch destination is computed by adding the signed relative displacement in the third instruction byte to the PC, after incrementing the PC to the first byte of the next instruction. No flags are affected.

Note:

When this instruction is used to test an output pin, the value used as the original data will be read from the output data latch, not the input pin.

Example: The accumulator holds 56H (01010110B). The instruction sequence

JBC ACC.3, LABEL1

JBC ACC.2, LABEL2

will cause program execution to continue at the instruction identified by the label LABEL2, with the accumulator modified to 52H (01010010B).

Operation: JBC

(PC) ¬ (PC) + 3

 if (bit) = 1

then (bit) ¬ 0

(PC) ¬ (PC) + rel

Bytes: 3

Cycles: 2

Encoding: 0 0 0 1 0 0 0 0 bit address rel. address

 

JC rel

Function: Jump if carry is set

Description: If the carry flag is set, branch to the address indicated; otherwise proceed with the next instruction. The branch destination is computed by adding the signed relative displacement in the second instruction byte to the PC, after incrementing the PC

twice. No flags are affected.

Example: The carry flag is cleared. The instruction sequence

JC LABEL1

CPL C

JC LABEL2

will set the carry and cause program execution to continue at the instruction identified by the label LABEL2.

Operation: JC

(PC) ¬ (PC) + 2

if (C) = 1

then (PC) ¬ (PC) + rel

Bytes: 2

Cycles: 2

Encoding: 0 1 0 0 0 0 0 0 rel. address

 

 

Bill of Material:-

Designator

Description

Comment

Value

89s51

Header, 20-Pin, Dual row

Header 20X2

 

BR

Full Wave Diode Bridge

Bridge1

 

C1

Capacitor

Cap

.22

C2

Capacitor

Cap

.1

C3

Polarized Capacitor (Radial)

35V

1000uF

C4

Polarized Capacitor (Radial)

Cap Pol1

470uf

C16

Capacitor

Cap

22pf

C17

Capacitor

Cap

22pF

C27

Polarized Capacitor (Radial)

Cap Pol1

10uf

D1

General Purpose Diode

1N4007

 

INPUT

 

 

 

LCD

LCD_162A

 

 

OUT

 

 

 

R15

Resistor

Res1

10K

RST

Switch

SW-PB

 

S1

Switch

SW-PB

 

S2

Switch

SW-PB

 

SIP

SIP Common Ground Resistor Pack

10K

 

T1

Transformer (Ideal)

Trans Ideal

 

U1

Low-Noise Micropower Precision Voltage Reference

ADR291GT9

 

VR1

Potentiometer

 

10K

X2

Crystal Oscillator

XTAL

12MHz

 

Designator

Description

Comment

Value

C1

Ceramic Cap

 

0.1uF/50

C6

Ceramic Cap

 

0.22uF/50

C7

Ceramic Cap

 

0.047uF/50

C8

Ceramic Cap

 

0.47uF/50

C9

Ceramic Cap

 

0.1uF/50

C10

Ceramic Cap

 

0.1uF/50

C11

Ceramic Cap

 

0.022uF/50

C12

Ceramic Cap

 

0.22uF/50

C13

Ceramic Cap

 

0.1uF/50

C14

Ceramic Cap

 

0.47uF/50

C15

Ceramic Cap

 

0.1uF/50

C16

Ceramic Cap

 

0.1uF/50

C17

Ceramic Cap

 

0.1uF/50

C18

Ceramic Cap

 

0.1uF/50

C19

Ceramic Cap

 

0.1uF/50

C20

Ceramic Cap

 

0.1uF/50

C21

Electro Cap (Radial)

 

2.2uF/16V

C22

Electro Cap (Radial)

 

2.2uF/16V

C23

Electro Cap (Radial)

 

22uF/16V

C24

Electro Cap (Radial)

 

33uF/16V

D1

Switching Diode

1N4148

 

D2

Switching Diode

1N4148

 

D3

Switching Diode

1N4148

 

D4

Switching Diode

1N4148

 

D5

Switching Diode

1N4148

 

D6

Switching Diode

1N4148

 

D7

Switching Diode

1N4148

 

D8

Switching Diode

1N4148

 

INPUT1

 

 

 

OUT1

Header, 4-Pin

 

 

Q1

PNP General Purpose Amplifier 25V/1.5A

S8550

 

Q2

PNP General Purpose Amplifier 25V/1.5A

S8550

 

Q3

PNP General Purpose Amplifier 25V/1.5A

S8550

 

Q4

NPN Bipolar Transistor

NPN

S8050

Q5

NPN General Purpose Amplifier 25V/1.5A

S8050

 

Q6

NPN General Purpose Amplifier 25V/1.5A

S8050

 

Q7

NPN General Purpose Amplifier 25V/1.5A

S8050

 

R1

Resistor

Res1

1M

R2

Resistor

Res1

1M

R3

Resistor

Res1

10K

R4

Resistor

Res1

100K

R5

Resistor

Res1

10K

R6

Resistor

Res1

100K

R7

Resistor

Res1

3.3M

R8

Resistor

Res1

10K

R9

Resistor

Res1

220K

R10

Resistor

Res1

3K3

R11

Resistor

Res1

1M

R12

Resistor

Res1

1M

R13

Resistor

Res1

470K

R14

Resistor

Res1

470K

R15

Resistor

Res1

100K

R16

Resistor

Res1

10K

R17

Resistor

Res1

100K

R18

Resistor

Res1

1M

R19

Resistor

Res1

220K

R20

Resistor

Res1

1M

R21

Resistor

Res1

10K

R22

Resistor

Res1

3.3K

R23

Resistor

Res1

1M

R24

Resistor

Res1

1M

R25

Resistor

Res1

100K

R26

Resistor

Res1

1M

R27

Resistor

Res1

1M

R28

Resistor

Res1

220K

R29

Resistor

Res1

100K

R30

Resistor

 

10M

R31

Resistor

 

10M

R32

Resistor

 

1M

R33

Resistor

 

100K

R34

Resistor

 

10M

R35

Resistor

 

10M

R36

Resistor

 

100K

R37

Resistor

 

100K

R38

Resistor

 

1M

U1

Quad Low-Power Operational Amplifier

LM324AD

 

U2

Quad Low-Power Operational Amplifier

LM324AD

 

U3

Dual Low-Power Operational Amplifier

LM358D