Biomedical engineering: bioinstrumentaion lab

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Question Description

Electrocardiography (ECG) is the process of recording action potentials of the heart over a period of time using electrodes placed on the skin. Electrodes sense small electrical potentials on the skin and the signal is amplified, conditioned, and displayed to give a representation of the heart’s electrical activity. The purpose of this project is to gain experience building and designing analog circuits to process the ECG signal. Student is required to write an individual report: includes: inro, summarized methods, data, results, discussion, and conclusion.

  1. Complete the hardware design of Labs 1-4 of the BSL PRO Signal Processing Breadboard Labs. Complete recordings for each Lab and review the analysis and data report sections.
  2. Turn in Data Reports for Lab 3 and Lab 5 (do not build the notch filter). For Lab 5, conduct Recording 2 – ECG and exclude data report questions 1b, 2, and 3. Please include graphs for questions 4 – 6.

Note: protocol of labs is attached some data collected pictures. 9 more data pictures can be uploaded privately, since I can't upload more than 5 files.

Biomedical engineering: bioinstrumentaion lab
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Biomedical engineering: bioinstrumentaion lab
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Biomedical engineering: bioinstrumentaion lab
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Biomedical engineering: bioinstrumentaion lab
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Biomedical engineering: bioinstrumentaion lab
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Biomedical engineering: bioinstrumentaion lab
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Biomedical engineering: bioinstrumentaion lab
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BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 06.22.11 Signal Processing Breadboard Lab Summary: Lab 1: Square Wave Oscillator Lab 6: QRS Detection: Band Pass Filter video 3 Lab 2: Instrumentation Amplifier video 1 Lab 7: QRS Detection: Absolute Value Circuit video 4 Lab 3: High Pass Active Filter Lab 8: QRS Detection: Low Pass Filter and Overall System Test Video 5-log Lab 4: Active Gain Block and Low Pass Filter Lab 5: Notch Filter for 50/60 Hz Rejection video 2 The Signal Processing Labs use the BIOPAC SS39L Signal Processing Breadboard, the SS39L Interface Cable, SS60L Interface Cable, and the BSLTCI-22 Breadboard Electrode Interface. Page 1 of 63 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 Signal Processing Background The human body can be studied by viewing the potential difference (Voltage) between strategically placed surface electrodes. Because surface electrodes are an easy, non-invasive way to obtain information about the body, they represent a good starting point for examining the types of electronic circuits used in Biomedical Engineering. In order to view and record the potential difference between surface electrodes, electronic circuits are used. Electrode leads, which are essentially wires, connect the electrodes to the circuit. Most signals from physiological activity have small amplitudes and must be amplified and processed before they can be viewed in a meaningful way. The good news is that the characteristics of biopotential amplifiers are much the same as any other amplifier. We will review the basics of amplifiers, with special emphasis on the biopotentials. 1. Gain. Physiological signals have amplitudes that range from several microvolts to a few millivolts. To drive display and recording equipment, most biopotential amplifiers have gains of 500 or greater. It is useful to use the decibel form of gain, which is obtained from linear form by the formula: Gain(dB)  20 log10 Linear Gain) 2. Common-mode rejection (CMR). The human body makes a reasonably good antenna, and will create electric potentials from electromagnetic radiation present in the atmosphere. A serious problem is 50/60 Hz radiation - present almost anywhere there is electric power. The problem become acute when the biopotentials we wish to monitor have useful energy in the 50/60 Hz range. CMR is the property of canceling any signals that are in common to both inputs, while amplifying differential signals (a potential difference between the inputs). Both AC and DC CMR are important for physiological signals. CMR is usually specified for a common-mode voltage change at a certain frequency. The common-mode rejection ratio (CMRR) is first obtained: CM ) CMRR  AD (VVOUT where AD is the differential gain of the amplifier VCM is the common-mode voltage present at both inputs of the amplifier VOUT is the output voltage result when the common-mode inputs are applied The logarithmic conversion of CMRR, common-mode rejection is defined as: CMR(dB)  20 log10 CMRR) 3. Frequency response. The bandwidth of a physiological amplifier should accurately amplify all the frequencies of importance in the signal, while rejecting those signals outside the bandwidth of interest. The bandwidth is defined as the difference between the low frequency cutoff and high frequency cutoff. The cutoff is defined at the point where the gain is 0.707 of the midpoint gain of the response, and is alternatively called the half power point ( 0.707 2  0.5) , or –3dB point, since  3.01(dB)  20 log10 0.707) . 4. Input impedance. A fundamental rule of measurement is to not allow the measuring device influence the signal under observation. An amplifier should exhibit high input impedance so as to not measurably attenuate physiological signals being measured. In the case of the ECG, the ECG electrode itself has low impedance, but skin impedance can range from 100 ohms to 1M ohm. Amplifier input currents cause potentials across the skin impedance that are amplified by the gain of the amplifier, causing large DC offsets in the amplifier output. 5. Noise and drift. Unwanted signals that contaminate physiological measurements, noise produced within amplifier circuitry is generally defined as those signals with components above 0.1Hz, while drift refers to the changes in baseline below 0.1Hz. Noise can be measured in microvolts peak to Page 2 of 63 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 peak ( V p  p ) or microvolts root mean square ( VRMS ). Sources of drift include offset voltage drift (varying input impedance), and gain drift, usually affected most by temperature. 6. Electrode polarization. Electrodes made of metal, and used with a electrolyte, such as the standard ECG Silver/Silver chloride electrode, form small potentials resulting from ion electron exchange between the electrode and the electrolyte (as in a battery). The challenge for the amplifier designer is to amplify the weak physiological signals in the presence of these polarized dc signals. Page 3 of 63 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 ECG Background The generation of electrical activity in the heart is characterized by mechanical events. During the period of diastole, the heart rests between beats, and assumes its maximum size while filling with blood that has been oxygenated by the lungs and venous blood from the body. Mechanical activity in the heart is called systole and is initiated by contraction of muscles surrounding the atria by electrical stimulation. The stimulations of the sinoatrial node (SA node), a bundle of nerves located in the right atrium, start the heartbeat and set the frequency of cardiac rhythm. This rhythm can be modified by nerve fibers external to the heart that function to control the hearts response to increases or decreases in the body’s demand for blood. Contractions of muscles comprising the atria are stimulated by impulses generated by the SA node. Impulses from the SA node are conducted along nerve fibers in the atrium to depolarize the atriovetricular node (AV node). AV node stimulation causes contraction of the muscles comprising the ventricles via the bundle of His and the Purkinje conducting system. The depolarization and repolarization of the SA node is followed by the depolarization and repolarization of the AV node – this is the electrical control system that initiates the muscle contractions necessary to maintain the heart’s pumping action. This nerve system generates the external action potentials known as electriocardiogram (ECG), which can be recorded by electrodes at the surface of the body. ECG waveform and heart function (from Biophysical Measurements, P. Strong, Tektronix Inc.) It is important to understand the basic functions of the heart as shown by the ECG waveform. The QRS spike is associated with the rapid depolarization of ventricular muscle immediately preceding its contraction. The P wave is the result of atrial depolarization and the T wave is caused by ventricular muscle repolarization. Monitoring this electrical generator, enclosed in a torso, is the function of electrocardiography. By attaching electrodes to certain places on the body, the small electrical potentials on the surface are sensed. The potentials can then be amplified, conditioned and displayed to give a representation of the heart’s electrical activity. Assuming we will be using the basic frontal plane cardiac vector – a standard placement of electrodes – we can construct a simple ECG monitor to record the potentials. Circuit requirements: The ECG QRS spike can range from 400 uV to 2.5 mV peak, and will require a voltage gain of 100 to 1000. ECG bandwidth has been standardized to make interpretation of the results uniform. Two filters with 3dB cutoffs are used – a high pass filter at 0.05Hz and a low pass filter at 100Hz. A 60Hz (or 50Hz) notch filter is used to attenuate nominal mains interference. Although the waveform of the ECG is considered as a low frequency AC signal, there can be significant DC offsets between the electrodes on the body (0 to ±20mV DC). With a voltage gain at +1000, a DC offset of 20mV will cause an amplifier to try to produce a signal at 20.0V, higher than typical power supplies permit. We must prevent DC offsets from swamping the AC signal of interest, and we do this with a high pass filter. Signals present on the electrodes higher than 100Hz contribute noise to the ECG that must be reduced to present an accurate view of the ECG. Potentials generated from muscle activity are undesirable in the ECG and are partially reduced with the low pass filter (it is required that a person being monitored for ECG remain relaxed and motionless.) There are numerous other potentials that are inadvertently amplified when using electrodes to monitor ECG. The mains power produces very high levels of EMI interference, which must be Page 4 of 63 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 carefully eliminated. The use of shielded electrodes, coupled into a differential amplifier, can reduce EMI mains interference dramatically. Other sources of EMI include radio stations, cell or portable phones, microwave sources, computers, and automotive ignition. We will not attempt to squelch all these sources of interference, although you may experience them in your circuits. Page 5 of 63 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 Breadboard Setup The SS39L Breadboard is designed to rapidly prototype the ECG circuitry without the use of soldering equipment. Close examination of the SS39L Breadboard reveals that there are five individual boards mounted on the plastic base. The top bus strip has a row of two power bus rows. Next is a strip that contains a 5x64x2 connection array, designed to easily accept 0.3” Dual In Line (DIP) integrated circuits (IC). Beneath the 5x64x2 strip is another power bus strip identical to the top strip. The BIOPAC lessons do not use or refer to the bottom two boards. The power busses are not labeled on the SS39L, so for safety and reliability, add the following labels:     Top Row: ‘-5’ Row above row A: ’G1’ Row below row J: ‘G2’ Next Row: ‘+5’ The power strips must be wired so that the top bus is connected to -5.0V (Green terminal), the bus above row A is GND (Black terminal), the bus below row J is also GND (Black terminal), and the last bus is connected to +5.0V (Red terminal). Needle nosed pliers are recommended for inserting wires into the breadboard. 1. Connect a Brown 1.0” jumper from the Black terminal (GND) to the bus above Row A (G1). Connect a Red 2.0” jumper from G1 to G2. 2. Connect a Yellow 4.0” jumper from the Red terminal (+5V) to the bus +5. 3. Connect a Brown 1.0” jumper from the Green terminal (-5V) to the bus -5. 4. Each bus is actually divided into two half busses. Bridge all the busses by adding four 0.3” Orange jumpers as shown below. Next, place all the integrated circuits and wire them to the power busses, adding the decoupling capacitors. 1. Place the LMC6484A with pin 1 in row F, column 55 2. Place an LM324 with pin 1 in row F, column 35 3. Place an LM324 with pin 1 in row F, column 24 4. Place an LM324 with pin 1 in row F, column 13 5. Connect four 0.01uF capacitors with one end in pin 4 of each IC, the other end to G2 bus. 6. Connect four 0.01uF capacitors with one end in pin 11 of each IC, the other end to G1 bus. 7. Check all capacitors for short circuits. 8. Place the BSLTCI-22 Breadboard Electrode Adapter with pin 1 in row A, column 48. Page 6 of 63 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 Power Verification BME ECG Board Layout with Integrated Circuits The following steps will apply +5V and -5V isolated power to the breadboard from the MP36/MP35. The MP36/MP35 power is limited to about 100ma. If the MP36/MP35 power is overloaded by the breadboard circuitry due to improper wiring, the MP36/35 may not perform acquisitions properly. 1. If inserted, remove the DB9 end of the SS39L cable from the MP36/MP35, and turn off the MP36/MP35. 2. Plug in the SS39L Cable Black (GND) banana plug into the Black terminal jack. 3. Plug in the SS39L Cable Red (+5) banana plug into the Red terminal jack. 4. Plug in the SS39L Cable Green (-5) banana plug into the Green terminal jack. 5. Plug in the SS39L Cable GND Reference pin into the breadboard GND bus G1. 6. Plug in the SS39L Cable SIGNAL pin into the breadboard GND bus G1. 7. Plug in the SS39L Cable DB9 plug into CH1 of the MP36/MP35. 8. Plug in the SS60L Cable DB9 plug into CH2 of the MP36/MP35. 9. Plug in the SS60L Cable SIGNAL pin into the breadboard GND bus G1. 10. Plug in the SS60L Cable GND pin into the breadboard GND bus G1. 11. Turn on power to the MP36/35. Verify 5V(±5%) and -5V(±5%) power buses with a DVM.  If at any time during the experiments the measured power busses drop below their rated values, turn off the MP36/35 and find the cause of the circuit overload in your breadboard wiring. 12. Start BSL PRO. Make a sample reading of the MP36/MP35 (Start). Verify that the reading is ~0.00V DC. If there is a problem with power that causes the MP36/MP35 startup routine to fail, the Busy light on the MP36/MP35 front panel will flash an error code sequence, and will not allow a recording to occur. The Busy light normally comes on for 1 or 2 seconds, blinks once for USB renumeration, stays on for 10-20 seconds for self-calibration, then turns off. The Busy light then monitors USB data transfers. Page 7 of 63 BSL PRO Signal Processing Breadboard Labs © BIOPAC 2005 Figure 1 – BME LAB SCHEMATIC – 1 of 2 Page 8 of 63 www.biopac.com BSL PRO Signal Processing Breadboard Labs © BIOPAC 2005 Figure 1 – BME LAB Schematic – 2 of 2 Page 9 of 63 www.biopac.com BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 Lab 1: Square Wave Oscillator Objectives: 1. Create a Square Wave Oscillator, which will be used to test the remaining circuits in the BME labs. 2. Approximate the magnitude of an ECG signal. Background: The step voltage has great value in analysis of amplifiers. The square wave generator built in this lab is used later to determine gain and AC-response of the remainder of the circuits in the BME Breadboard Labs. Square wave generators are available commercially, but self-test is an important part of most modern medical equipment, so it is included as the first project. A Square Wave Oscillator can be designed using the opamp as a Schmitt comparator, using a single quad opamp (Fig. 1.1). Fig. 1.1 Schematic for SS39L Breadboard Lab 1 Referring to the schematic, the Square Wave output voltage is Vo, and the voltage across the capacitor is Vc. The voltage across the comparator inputs Vi is the difference of (Vc – ßVo). Assuming an ideal comparator response, with the voltage Vi < 0, the capacitor charges exponentially toward Vo through the RC combination. The output stays at Vo until Vc=+ßVo, which causes the comparator output to reverse to – Vo. Vc charges exponentially toward –Vo. The output will continue this cycle, with the period T: T  2 R3C1 ln1  2 R1 ) R2 The output will swing rail to rail. With the LMC6484 opamp (supplied with the SS39L), expect ~9.8 Vpp signal out, with some offset due to mismatch between positive and negative rail levels. This will also affect the square wave symmetry. The oscillator is followed by an amplifier which provides a divide by 19.6 (0.5 Vpp) which, in turn, is followed by another amplifier that divides by 200 (2.5 mVpp). The 2.5 mVpp square wave is a signal level very close to the expected ECG signal, and can be used to test the instrumentation amp gain, as well as the high and Low Pass filters. The 0.5 Vpp will be used for the common mode test of the instrumentation amp. Page 10 of 63 Lab 1 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 Laboratory: Hardware Setup 1. Build the square wave oscillator and divisor functions per the Lab 1 Schematic (Fig. 1.1). 2. Connect the interface cables to the MP36/MP35 unit. a. SS39L into CH1 on the MP36/MP35 b. SS60L into CH2 on the MP36/MP35 3. Connect the interface cables to the breadboard to monitor the square wave outputs. a. MP36/MP35 CH1 signal input to 0.5 Vpp (IC1 pin 7). b. MP36/MP35 CH2 signal input to 2.5 mVpp (IC1 pin 8). c. Connect the negative leads to the ground bus. Software Setup Set the BSL PRO software for recording as follows:  Use the SqWvGen.gtl template (File > Open > SqWvGen.gtl) to simplify setup. 1. MP36/MP35 > Set up Channels: a. Enable Acquire Data, Plot On Screen, and Enable Display Value for CH1 and CH2, and type a label for each channel. b. Click the “wrench” icon for CH1 and set parameters as follows: i) Filters 1, 2, 3: None; Gain: x50, Offset: 0; Input coupling: DC ii) Scaling 10 mV  50 mV and -10 mV -50 mV. Scaling is set at x5 to account for the probe’s ÷5 internal resistor scaling. Page 11 of 63 Lab 1 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 iii) | c. Click the “wrench” icon for CH2 and set parameters as follows: i) Filter 1,2,&3: None; Gain: x2000; Offset: 0; Input coupling: DC ii) Scaling 10 mV  50 mV and -10 mV  -50 mV. Scaling is set at x5 to account for the probe’s ÷5 internal resistor scaling. d. Click OK as required to exit Set up Channels. 2. MP36/MP35 > Set up Acquisition a. Mode: Record, Save Once, PC Memory b. Sample Rate: 5000 c. Acquisition Length: 5 seconds (minimum) 3. Use two measurement rows. To set up, select (File > Preference > General). Show 2 measurement rows. Show 3 digits of precision. Page 12 of 63 Lab 1 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 Recording 1. Press the “Start” button in the software window to begin recording. 2. After at least 5 seconds, press the “Stop” button. Analysis 1. a. b. c. 2. Set the following measurements for each channel: Freq (frequency) d) Stddev (standard deviation) Mean e) P-P (peak-to-peak) Delta T (time) Select a section of the high output level for each channel, avoiding any ringing at the transitions, and measure Mean. 3. Select a section of the low output level for each channel, avoiding any ringing at the transitions, and measure Mean. 4. Select one square wave cycle and measure Freq, Delta T, and Stddev, P-P for each channel.  Standard deviation of a square wave is ½ the P-P value. Standard deviation is equal to RMS, but with the added bonus of DC removal. 5. Do you notice “noise” on the 2.5mVpp signal? Magnify a section of the signal to measure the frequency and amplitude. Page 13 of 63 Lab 1 BSL PRO Signal Processing Breadboard Labs www.biopac.com © BIOPAC 2005 Data Report for Lab 1: 1. Report all findings of the Lab. Channel High Mean Low Mean Freq Delta T Stddev P-P CH1 CH2 2. Include recorded graphs of the results.  To paste graphs into an open Word document, select Edit > Clipboard > Copy Graph in BSL PRO and then right-click in the Word document and select paste. 3. Review the findings. a. Is the square wave symmetrical (are the periods for both halves of the cycle equal)? Yes No b. What is the ratio of the noise to the 2.5mVpp signal? c. Report any discrepancies from actual results and expected results.  Expected results: Frequency: 1.0 Hz ±20%; Output Voltage at voltage dividers: 0.5 Vpp and 2.5 mVpp ±10% d. Report suspected causes for any discrepancies. e. How was /could the problem(s) be fixed? 4. What is the correlation between the Delta T and Freq measurements? (answer as an equation) 5. Why is the Stddev measurement more precise than the P-P measurement? End Lab 1 Page 14 of 63 Lab 1 BSL PRO Signal Pr ...

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