Chua (2005) - Blood Pressure Meter (Freescale An 1571)
Chua (2005) - Blood Pressure Meter (Freescale An 1571)
Chua (2005) - Blood Pressure Meter (Freescale An 1571)
Application Note
AN1571
Rev 1, 05/2005
INTRODUCTION
11
0.33
1
LM324N
U1a
11
R1
1k
C1
33u
R2
150k
Vo
1M
4
3
Vi
C2
R3
+5.0V
P1 =
2R1C1
P2 =
2R3C2
10
0
-10
Attenuation (dB)
-20
Oscillation Signal (1 Hz)
-30
-40
-50
-60
-70
-80
0.01
0.1
10
100
Frequency (Hz)
AN1571
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Sensors
Freescale Semiconductor
3
2.5
Vi (Volts)
2
1.5
Oscillation signal is extracted here
1
0.5
0
10
15
20
25
30
35
40
Time (seconds)
3.5
MAP
SBP
DBP
Vo (Volts)
2.5
2
1.5
1
0.5
0
10
15
20
25
30
35
Time (seconds)
counts is the range of the A/D converter. VRH and VRL are the
reference voltage inputs to the A/D converter. The resolution
is defined by the following:
Count = [(VXdcr - VRL)/(VRH - VRL)] x 255
The count at 0 mm Hg = [(0.2 - 0)/(3.8 - 0)] x 255 14
The count at 300 mm Hg = [(3.8 - 0)/(3.8 - 0)] x 255 255
Therefore the resolution = 255 - 14 = 241 counts. This
translates to a system that will resolve to 1.24 mm Hg.
The voltage divider consisting of R5 and R6 is connected to
the +5 volts powering the system. The output of the pressure
sensor is ratiometric to the voltage applied to it. The pressure
sensor and the voltage divider are connected to a common
AN1571
Sensors
Freescale Semiconductor
AN1571
4
Sensors
Freescale Semiconductor
GND
Vs
C5
0.33u
Vout
Pressure Sensor
MPXV5050GP
+5.0 V
3
2
0.33u
C2
24k
+5.0 V
R4
GND
3 Input Output 1
R3
MC78L05ACP
+5.0 V
1M
5.0 V Regulator
10k
R0
R1
C1
1k
33u
+5.0 V
LM324N
R2
150k
C8
1
Buzzer
100n
C7
C6
330u
100R
100u
C3
VDD
OSC2
22p
X1
22p
PD0/AN0
PD1/AN1
PD2/AN2
PD3/AN3
PD4/AN4
PD5/AN5
PD6/AN6
PD7/AN7
14
13
12
11
9
5
4
3
+5.0 V
MC68HC05B16CFN
PB0
PB1
PB2
PB3
PB4
PB5
PB6
PB7
VRH
PLMA
VRL
PLMB
PA0
PC0
PA1
PC1
PC2/ECLK PA2
PA3
PC3
PA4
PC4
PA5
PC5
PA6
PC6
PA7
PC7
20
21
49
48
47
46
45
44
43
42
RD
TCAP1
TCAP2
/RESET
/IRQ
OSC1
4MHz
2
TCMP1
1 TCMP2
52 TDO
51 SCLK
10
17
R10
10M
39
38
37
36
35
34
33
32
8
7
31
30
29
28
27
26
25
24
50
22
23
18
19
+5.0 V
C4
16
+5.0 V
+5.0 V
R5
11
4.7k + 36R
R8
4.7k
LED
Sensors
Freescale Semiconductor
+5.0 V
1 Reset Input
MC34064
GND
2
3
R9
15k
R6
AN1571
9.0 V Battery
12
27
26
25
24
15
14
13
16
23
22
21
20
19
18
17
DP2
G2
F2 DP E
A2
D 1
B2
C2
C
D2
E2
DP
LCD5657
DP1
G1
F1
4
A1
B1
C1 DP
D1
3
E1
34
7
6
37
36
35
28
L
40
BP
1
BP
8
DP3
32
G3
31
F3
30
A3
A
29
B3
11
C3
10
D3
9
E3
G4
F4
A4
B4
C4
D4
E4
SOFTWARE DESCRIPTION
Upon system power-up, the user needs to manually pump
the cuff pressure to approximately 160 mm Hg or 30 mm Hg
above the previous SBP. During the pumping of the inflation
bulb, the microcontroller ignores the signal at the output of the
VO (volt)
450 ms
1.75
Premature Pulse
-8.5
-8.3
-8.1
-7.9
-7.7
-7.5
-7.3
-7.1
Time (second)
SELECTION OF MICROCONTROLLER
Although the microcontroller used in this project is
MC68HC05B16, a smaller ROM version microcontroller can
also be used. The list below shows the requirement of
CONCLUSION
This circuit design concept may be used to evaluate
Freescale pressure sensors used in the digital blood pressure
meter. This basic circuit may be easily modified to provide
suitable output signal level. The software may also be easily
modified to provide better analysis of the SBP and DBP of a
person.
REFERENCES
Lucas, Bill (1991). An Evaluation System for Direct
Interface of the MPX5100 Pressure Sensor with a
Microprocessor, Freescale Application Note AN1305.
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Freescale Semiconductor
Main Program
Initialization
Clear I/O ports
Repump?
Output a high
frequency
musical tone
Display "Err"
Output a low
frequency alarm
Exhaust cuff
before repump
Exhaust cuff
before repump
AN1571
Sensors
Freescale Semiconductor
AN1571
Rev. 1
05/2005