BE 312 Lab #8
Lab 8: ECG Noise and Filtering
I.
Background
The Electrocardiogram (ECG/EKG) is an electrical signal produced by the heart muscle. It has an amplitude
of about 1mV, so a good amplifier is necessary. Electrical noise or electromagnetic
interference (EMI), is generated by many common appliances, such as: power lines, lights, computers, cell
phones, etc. When the ECG signal is amplified the noise is amplified as well and often swamps the ECG
signal. Signal conditioning the ECG signal is necessary to acquire a good quiet ECG.
The IX-TA-220 Recorder has the ability to output through the Stimulator any signal that is being
recorded on its input, including the iWire ports. In this lab, we are going to perform two experiments.
Experiment 1 focuses on using software filters to remove noise from the ECG signal. Experiment 2 uses a
hardware filter that you assemble on the breadboards to remove noise from the ECG signal.
Experiment 1
1) Record the ECG from the subject using the iWire-B3G.
2) Introduce some 60Hz noise into the ECG recording, by spreading the electrode cables.
3) Identify the frequency of the noise using the spectrum analyzer.
4) Filter the signal using various software filters.
5) Compare the ECG recorded by the iWire-B3G with the filtered ECG.
Experiment 2
1) Record the ECG from the subject using the iWire-B3G.
2) Output the signal recorded by the iWire-B3G using the S1 Stimulator.
3) Send the ECG signal to the breadboard, using the C-BNC-BB cable.
4) Filter the signal on the breadboard.
5) Send the filtered signal back to the IX-TA-220, using the C-DIN-BB cable.
a. The C-DIN-BB cable also provides +5V and -5V power to power the circuit.
6) Compare the ECG recorded by the iWire-B3G with the filtered ECG
II. Setup
Equipment Required
• PC or Mac Computer
• IX-TA data acquisition unit and power supply
•
USB cable
• ROAM Wireless ECG
•
Labscribe: Settings>BioInstrumentation>ECGFilter-ROAM
• C-DIN-BB: Din to Breadboard cable
• C-BNC-BB: BNC to Breadboard cable
A-BREADBOARD: Breadboard
•
•
Alcohol swabs
•
Disposable ECG electrodes
1 BE 312 Lab #8
Build the Filter Circuit
The first step is to construct a filter on the breadboard. The “breadboard” is a board that is used to create
simple prototype electrical circuits without circuit boards or soldering to connect the components.
An example is shown in Figure 1.
GLOBAL
SPECIALTIES
alalalala
Va Vb Ve
Figure 1. Example breadboard. The one you use may look slightly different.
Breadboards have internal electrical connections that are common for all breadboards. Some holes are
are electrically connected to each other inside the breadboard, while others are not. As shown in Figure
2, the long rows or columns of holes (usually indicated with a blue line, or black line, or red line along
them) are all electrically connected inside the board. Thus a wire plugged into one of these holes will be
electrically connected to all the others in that long row or column.
The central array of holes are connected differently. These are shown with the letters (A B C D E), (F G
HIJ), and numbered rows (1,2,3,4...). In each row A-E are all electrically connected. And F-J are
electrically connected. But, (A-E) are not connected to (F-J). Rows are not connected either. Also note
that if there are multiple (A-E) or (F-J) columns, they are all separate and not connected.
2 BE 312 Lab #8
SPECIALITES
5
ABCD
FGH
5
10
10
All the holes in this row are
electrically connected
in the breadboard
All the holes in this row are
electrically connected
in the breadboard (5 holes)
All the holes in this row are
electrically connected
in the breadboard (5 holes)
All the holes in this column are
in the breadboard.
electrically connected
A and B are separate, and are not
electrically connected (although the
holes in A are connected to each other
and the holes in B are connected
to each other).
Figure 2. Close-up of the breadboard explaining the internal connectivity.
For this lab, you will use a second order (2-pole) low pass filter as the hardware filter. The schematic is
shown in Figure 3.
C2
0.22μF
U1
R2
+
R1
Output_A5
S1_Input
V1
TL062
V2 30.1k
30.1k
C1
0.22µF
5v
-5v
Figure 3. Schematic of the low
pass filter you will build and use.
This filter is a Sallen Key 2-pole low pass filter. Its job is to remove 60Hz electrical noise picked up
from fluorescent lights, computers, and AC power lines. Figure 4 shows this circuit as a “Fritzing
diagram” which is a picture representation of what your circuit on the breadboard should look like
3 BE 312 Lab #8
when completed.
0000000
Figure 4. Fritzing diagram of the low
pass
filter.
TL062
Construct the circuit as shown and double check that the wires and components are all connected
correctly. Once this is done, go to the breadboard setup and connect to the iWorx.
Breadboard Setup
1. Insert the BNC connector on the end of the C-BNC-BB cable into the S1 stimulator port of the
TA.
2. Connect the other end of the C-BNC-BB cable to the breadboard.
3. Insert the DIN8 connector of the C-DIN-BB cable into the A5 port of the TA.
4. Connect the other end of the C-DIN-BB cable to the breadboard.
See Figure 5 and Figure 6 for pictures of these connections. Do these after the circuit has been assembled.
Once everything is connected, continue to the next step and place the ECG electrodes.
4 BE 312 Lab #8
C-DIN-BB Ground
C-BNC-BB Ground
C-BNC-BB Signal
C-DIN-BB +5 V
C-DIN-BB-5 V
C-DIN-BB+ Input
C-DIN-BB- Input
HI
Vb
a
abcde
TO
220
25
Figure 5. Photo of the breadboard with circuit. Note the wires to be connected to the iWorx box.
ECG Setup
BREADBOARD
iWorx TA-ROAM
RAM
A1
ROAM Wireless
A2
iWire
A3
A4
A5
A6
A7 PT
2
C-BNC-BB
LV Stim
$1
$2
Figure 6. Breadboard connection to the iWorx box.
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