EGR 1200 Fall 2011
Automatic Blood Pressure Measurement
Lab 4
Oscillation Signal Amplifier and Electronic Blood
Pressure Measurement
Electrical and Computer Engineering
Villanova University
General Overview of Lab 4
Purpose: The purpose of Lab 4 is to give you a feel for electronic
circuit construction, characterization, and verification, which, in
addition to design and simulation, are necessary aspects of
electronic engineering.
Method: We will apply the oscillometric method and implement an
oscillation signal amplifier circuit to extract information from the
pressure sensor signal. This will allow us to make an electronic
measurement of blood pressure without any additional sensor(s).
Major Procedures:
I. Implementing the oscillation signal amplifier circuit.
II. Setting up the digital oscilloscope to acquire signals.
III. Acquiring signals using the oscilloscope.
IV. Determining the blood pressure.
I. Implementing the oscillation signal
amplifier circuit
1. Build the circuit to correspond to the diagrams and photos shown in
in the next few pages.
2. Use color wires as follow: RED for +9V, BLACK for -9V, GREEN for
0 V (GND), and YELLOW for pressure signal from input to output of
the amplifier.
3. Double check that the electrolytic caps have their negative terminal () at the lower potential. That is, for the capacitor across the +9V
node, the capacitor’s negative terminal (-) is connected to 0 V. For
the -9V node, its capacitor’s negative terminal (-) is connected to -9V
and the positive terminal (+) is connected to 0 V.
4. You can either use the resistor color code or an ohmmeter to
determine the resistance value for the resistors R1, R2, and R3.*
5. Show the completed circuit construction to your instructor/TA
before proceeding further.
*See the link below for resistors and the color code:
http://samengstrom.com/nxl/3660/4_band_resistor_color_code_page.en.html
Oscillation Signal Amplifier Circuit Schematic
Resistors:R1, R2, & R3
Electrolytic caps: C1, C2, C3, & C5
Ceramic cap C4
-9 VDC (Black wire)
(Yellow wire:Input)
Op-amp
(Yellow wire: Output)
+9VDC (Red wire)
0 VDC (GND) (Green wire)
4
Oscillation Signal Amplifier Circuit Breadboard Diagram
5
Oscillation Signal Amplifier Circuit Breadboard Photo
NEGATIVE SIDE of CAP
C2
C3
C5
R3
R1
C4
Connector
Location from
Pressure/Power
Supply Board
Oscillometric
Signal
R2
LM324
U1A
+9V (Red)
0V
(Green)
Pressure Signal
-9V (Black)
NEGATIVE SIDE of CAP
C1
6
Oscillation Signal Amplifier Circuit (Zoom in at Op Amp Chip)
Oscillometric
Signal
R1
R3
R2
LM324
U1A
1
2
3
4
Notch
11
C4
Pressure Signal
7
II. Setting up the digital oscilloscope to
acquire signals
1.
2.
3.
4.
5.
6.
7.
On the oscilloscope probes, slide the yellow switches to the 10X position
to set the probe attenuation.
Press the AUTO button to start the oscilloscope at a default state.
Press the CH 1 button of the VERTICAL system. Verify that under the
display word “Probe” is the text indicating “10X.” This setting indicate that
we are using a 10X probe as set in step 1 above.
Press the CH 2 button of the VERTICAL system. Verify that under the
display word “Probe” is the text indicating “10X.”
Turn the SCALE knob of the HORIZONTAL system to adjust the time scale
to 1.0 s/div. The display should show “Time 1.000s.”
Press the CH 1 button of the VERTICAL system. Turn the SCALE knob to
adjust the voltage per division for channel 1 to 0.5 V/div. The display
should show “CH1 500 mV.”
Press the CH2 button of the VERTICAL system. Turn the SCALE knob to
adjust the voltage per division for channel 2 to 1.0 V/div. The display
should show “CH2 1.00 V.”
II. Setting up the digital oscilloscope to
acquire signals
8.
Press the CH 1 button. Select the gray softkey next to the displayed word
“Coupling” and keep pressing until “GND” is highlighted. GND, which
stands for ground, will be our reference point. Now, using the POSITION
knob within the VERTICAL system, adjust the knob such that the display
shows “POS=0.00mV.” Press the CH 1 button again and using the same
gray softkey, press until the word “DC” is shown. This DC indication tells us
that we are directly coupling the pressure signal to the scope.
9. Press the CH 2 button and repeat the step above for channel 2. By setting
both CH 1 and CH 2 GND to the center of the vertical display, we are
setting the reference level for our signal to the center of this display. This
then tells us that any signal waveform above the vertical center is a
positive voltage and any signal waveform below is a negative voltage.
10. Press the MENU button of the HORIZONTAL system. Under the display
word “Time Base,” set the time base to “Roll.”
11. Press the RUN/STOP button to put the oscilloscope in RUN mode.
12. Show your oscilloscope setup to your instructor/TA before proceeding
further.
III. Acquiring the signals using the oscilloscope
Use the diagram and photos on the next page to aid with steps 1-3 below.
1. Connect the white tubing from the cuff to the pressure sensor on the
backside of the pressure sensor/power supply board.
2. Attach the oscilloscope probes to the oscillation signal amplifier circuit
breadboard.
a. Connect CH 1 probe to the test point for Pressure Signal.
b. Connect CH 2 probe to test point for the Oscillometric (Oscillation) Signal.
3. Connect the pressure sensor/power supply board to your board using the
ribbon connector. Pin 4 of the connector should be in the same row as the
Yellow Wire for Pressure Signal. Move the board’s switch to the ON
position.
4. Place the cuff securely on your arm as done in Lab 1 Manual Blood
Pressure Measurement and then press the START on the OMRON blood
pressure meter to start inflating the cuff.
5. Press the RUN/STOP button to stop the signal acquisition. Make sure that
the oscilloscope has acquired sufficient number of peaks of the
oscillation signal after the maximum peak had appeared.
Pressure Sensor Board to Breadboard Connections
Ribbon Connector
Pressure Signal
from Cuff
Pin 1
MPX5050 Pressure
Sensor
BACK
FRONT (with connect to
Breadboard)
11
Pressure Sensor/Power Supply Board
Schematic
(Red wire)
(Black wire)
(Yellow wire)
(Green wire)
12
Measurement Setup
Digital
Oscilloscope:
Captures pressure
and oscillometric
signals
Omron BP Meter:
Auto Inflate/Deflate
Cuff
Pressure Sensor &
Power Supply Board:
Outputs pressure
(electrical) signal and
supplies +9,-9 volts DC
Breadboard of Amplifier/Filter Circuit
to extract oscillometric signal from
pressure sensor
13
IV. Determining blood pressure
1.
2.
3.
4.
Push the Cursor button in the MENU system. On the display, using the
gray softkeys choose “Track” for the “Mode”, “CH1” for “Cursor A”, and
“CH2” for “Cursor B.” Notice also on the display under “CurA—” and
“CurB—” there is a symbol of a clockwise rotation. This symbol refers to
the knob to the left of the MENU system panel. If the symbol is
highlighted under “CurA—,” for example, that means turning this knob
moves cursor A. To select cursor B to correspond to the knob, push the
gray softkey next to “CurB--.”
Using Cursor B find the maximum valid peak for the oscillation signal.
Record the voltage value displayed by the Cursor B. Select Cursor A and
move it to the time position and record its voltage value. This latter
value represent the mean arterial pressure in terms of voltage.
Multiply the maximum peak recorded value by 0.8 and 0.9 to obtain the
peak values for the systolic and diastolic pressures, respectively.
Turn the POSITION knob in the HORIZONTAL system to locate peaks on
the oscillation signal that closely match the calculated values from above.
As you find a closest peak, record its value and the corresponding voltage
value on Cursor A. This latter value represents the magnitude of the
pressure signal in voltage.
Appendix: Saving the signals to file
You can save the display plots onto a bitmap file. To do so,
1. Press the STORAGE button in the MENU system.
2. Select the gray softkey to the right of the display word
“Storage.” Keep pressing the button until “Bit Map” is
highlighted.
3. Select the gray softkey to the right of the display word
“External.” This will allow you to save to a USB key drive.
4. A new set of display words are shown. Press the gray softkey
to the right of the display word “New File.”
5. After a new window popped up, type in the filename. Turn
the knob with the clockwise symbol to move between the
characters and press the knob to select the desired character.
15
Lab 4 Sensors and Analog Electronics
Instructor/TA Sign Off Sheet & Report Form
1.
2.
3.
4.
Breadboard construction successfully completed:_____________________________
Oscilloscope properly configured for measurement:___________________________
Pressure and oscillometric signal successfully captured:________________________
Measurements verified:_________________________________________________
Measured Max.
Osc. Peak
Amplitude (V)
Calculated Osc.
Peak Amplitude
(V)
Measured Osc.
Peak Amplitude
(V)
Corresponding
Measured
Pressure Signal
(V)
Measured
Pressure Signal
(mm Hg)
Mean Arterial
Pressure
Systolic Pressure
Diastolic Pressure
5.
Based upon your implementation of the oscillometric method, discuss the advantages and
disadvantages of this method.