The document describes implementing pulse oximetry using a GreenPAK SLG46140 mixed-signal array device. It discusses driving red and infrared LEDs with pulse-width modulation to illuminate a finger, acquiring the signal from an infrared sensor using the device's ADC, and extracting blood oxygen saturation measurements from the signal based on light absorption properties. The implementation includes circuitry for the finger probe, programming the GreenPAK for LED control, ADC sampling and basic processing to transmit data for further processing. Extensions mentioned include integrating the GreenPAK with a microcontroller and improving signal processing for more accurate measurements.
DENOISING OF ECG SIGNAL USING FILTERS AND WAVELET TRANSFORMIJEEE
This paper presents a comparison of methods for denoising the Electrocardiogram signal. The methods are applied on
MIT-BIH arrhythmia database and implemented using MATLAB software.
Design of an IOT based Online Monitoring Digital StethoscopeIJAAS Team
Acoustic stethoscopes have low sound levels. Digital stethoscope overcomes this issue by amplifying body sounds electronically. As the sound signals are transmitted electronically, it can be wireless and can provide noise reduction. Acoustic stethoscope can be changed into a digital stethoscope by inserting an electric capacity microphone onto its head. Heart sounds received from the microphone are processed, sampled and sound signals are converted analog to digital and sent wirelessly using the Internet of Things(IOT) techniques, so that multiple doctors can do auscultation and monitor conditions of the patient.
DENOISING OF ECG SIGNAL USING FILTERS AND WAVELET TRANSFORMIJEEE
This paper presents a comparison of methods for denoising the Electrocardiogram signal. The methods are applied on
MIT-BIH arrhythmia database and implemented using MATLAB software.
Design of an IOT based Online Monitoring Digital StethoscopeIJAAS Team
Acoustic stethoscopes have low sound levels. Digital stethoscope overcomes this issue by amplifying body sounds electronically. As the sound signals are transmitted electronically, it can be wireless and can provide noise reduction. Acoustic stethoscope can be changed into a digital stethoscope by inserting an electric capacity microphone onto its head. Heart sounds received from the microphone are processed, sampled and sound signals are converted analog to digital and sent wirelessly using the Internet of Things(IOT) techniques, so that multiple doctors can do auscultation and monitor conditions of the patient.
Design and Analysis of CMOS Instrumentation AmplifierIJEEE
This paper presents the design and analysis of CMOS Instrumentation Amplifier in terms of gainas a performance metric. CMOSInstrumentation Amplifier has been designed using three Operational Amplifiers. Two basic op-amps have been used at the input stage and the output stage have been analysed for three different configurations. These configurations are: basic op-amp, body bias op-amp and folded cascode op-amp. A comparison has been drawn for all the three configurations.Most of the previous work has been done usingthe same type of op-amp at both the input and output stages of instrumentation amplifier. To obtain the desirableGain, focus has been laid upon transistor sizing for designing. The design models have been implemented using Cadence Virtuoso Analog Design Suite in 0.18µm CMOS technology.The simulations have been analysed in detail. A significant gain improvement has been observed in the circuit design with body bias and folded cascode as compared to the basic cascade design.
ECG COMPRESSION USING
FFT
The electrocardiogram (ECG) is a diagnostic tool that is routinely used to assess the electrical and muscular functions of the heart. Sometimes it is required to send the ECG signals from one place to another place. The ECG signals are compressed at first to reduce the amplitude and frequency and then transferred. ECG signals are compressed by using many techniques. One of the most important technique is FFT.
FFT (Fast Fourier Transform) is a technique used to convert analog signal to digital signal.
In FFT, The total process takes five steps:-
1) Input signal
2) Compression (counter A)
3) Compression (counter B)
4) Recovery of the original signal by using IFFT
5) Error checking
Now the detailed explanation of the above steps is given below
At first the input signal (ECG signal) is taken.
There are two stages for compression. In first stage of compression there is a counter A. It identifies the non-zero values of the signal before compression. After compression if the length of the compressed signal is less than the length of the actual signal, then zero padding is done to make equal the lengths of compressed and actual signal.
Now the signal is passed through the counter B. It identifies the non-zero values after the compression of the signal. Now after compression if the length of the compressed signal is greater than the length of the actual signal, then TRUNCATION of the signal is done.
Now by applying IFFT (Inverse Fast Fourier Transform) the original ECG signal is recovered.
The Error is checked at the last stage.
Compression ratio is given by
CR=(B-A)/B *100
CR-Compression ratio
A-compression in counter A
B-compression in counter B
Compression ratio is a major factor to determine how much compression the signal undergoes.
The compressed signal contains only positive values.
Thus ECG signal is compressed by using FFT technique.
Applications:-
• It finds application in hospitals, when a patient’s report is to be send to another doctor in prenomial place.
High Gain, Low Noise Instrumentation Amplifier Using Three Operational Amplif...IJEEE
This paper investigate the performance ofInstrumentation amplifier (INA) using three operationalAmplifier. The proposed circuit works for low input voltageequalised to the heart beat of the human being to analyses theECG (Biomedical application) response. The analyses ofGain, Bandwidth, Unity GBW, Phase margin and outputnoise for operational amplifier used in INA and For the INAGain, Bandwidth, output noise and power Dissipation areanalysed. The proposed circuit designed on UMC 180nmCMOS technology file and all the simulation done onCADENCE SPECTRE Simulator.
Instrumentation: Liquid and Gas Sensing (Design Conference 2013)Analog Devices, Inc.
This session focuses on liquid and gas sensing in instrumentation applications.
Liquid Sensing:
Visible light absorption spectroscopy and colorimetry are two fundamental tools used in chemical analysis. Most of these light-based systems use photodiodes as the light sensor, and require similar high input impedance signal chains. This session examines the different components of a photodiode amplifier signal chain, including a programmable gain transimpedance amplifier, a hardware lock-in amplifier, and a Σ-Δ ADC that can measure a sample and reference channel to greatly reduce any measurement error due to variations in intensity of the light source.
Gas Sensing:
Many industrial processes involve toxic compounds, and it is important to know when dangerous concentrations exist. Electrochemical sensors offer several advantages for instruments that detect or measure the concentration of toxic gases. This session will describe a portable toxic gas detector using an electrochemical sensor. The system presented here includes a potentiostat circuit to drive the sensor, as well as a transimpedance amplifier to take the very small output current from the sensor and translate it to a voltage that can take advantage of the full-scale input of an ADC.
P-Wave Related Disease Detection Using DWTIOSRJVSP
: ECG conveys information regarding the electrical function of the heart, by altering the shape of its constituent waves, namely the P, QRS, and T waves. ECG Feature Extraction plays a significant role in diagnosing most of the cardiac diseases. This paper focuses on detection of the P-wave, based on 12 lead standard ECG, which will be applied to the detection of patients prone to diseases. The ECG signal contains noise and that noise is removed using Bandpass filter. After elimination of noise, we detect QRS complex which help in detecting the P-Wave. P-wave morphology can be determined in leads II as monophasic and V1 as biphasic during sinus rhythm. DWT provides a value that helps in estimating features of the P-Wave. This detects the diseases that occur when the P-wave is abnormal. The method has been validated using ECG recordings of 250 patients with a wide variety of P-wave morphologies from Database
Distance measuring unit with zigbee protocol, Ultra sonic sensorAshok Raj
With Zigbee protocol, developed a distance measurement unit using an ultrasonic sensor, Arduino and X-bee trans-receiver for communication between displays and monitoring unit.
Software used: Arduino
Design and Analysis of CMOS Instrumentation AmplifierIJEEE
This paper presents the design and analysis of CMOS Instrumentation Amplifier in terms of gainas a performance metric. CMOSInstrumentation Amplifier has been designed using three Operational Amplifiers. Two basic op-amps have been used at the input stage and the output stage have been analysed for three different configurations. These configurations are: basic op-amp, body bias op-amp and folded cascode op-amp. A comparison has been drawn for all the three configurations.Most of the previous work has been done usingthe same type of op-amp at both the input and output stages of instrumentation amplifier. To obtain the desirableGain, focus has been laid upon transistor sizing for designing. The design models have been implemented using Cadence Virtuoso Analog Design Suite in 0.18µm CMOS technology.The simulations have been analysed in detail. A significant gain improvement has been observed in the circuit design with body bias and folded cascode as compared to the basic cascade design.
ECG COMPRESSION USING
FFT
The electrocardiogram (ECG) is a diagnostic tool that is routinely used to assess the electrical and muscular functions of the heart. Sometimes it is required to send the ECG signals from one place to another place. The ECG signals are compressed at first to reduce the amplitude and frequency and then transferred. ECG signals are compressed by using many techniques. One of the most important technique is FFT.
FFT (Fast Fourier Transform) is a technique used to convert analog signal to digital signal.
In FFT, The total process takes five steps:-
1) Input signal
2) Compression (counter A)
3) Compression (counter B)
4) Recovery of the original signal by using IFFT
5) Error checking
Now the detailed explanation of the above steps is given below
At first the input signal (ECG signal) is taken.
There are two stages for compression. In first stage of compression there is a counter A. It identifies the non-zero values of the signal before compression. After compression if the length of the compressed signal is less than the length of the actual signal, then zero padding is done to make equal the lengths of compressed and actual signal.
Now the signal is passed through the counter B. It identifies the non-zero values after the compression of the signal. Now after compression if the length of the compressed signal is greater than the length of the actual signal, then TRUNCATION of the signal is done.
Now by applying IFFT (Inverse Fast Fourier Transform) the original ECG signal is recovered.
The Error is checked at the last stage.
Compression ratio is given by
CR=(B-A)/B *100
CR-Compression ratio
A-compression in counter A
B-compression in counter B
Compression ratio is a major factor to determine how much compression the signal undergoes.
The compressed signal contains only positive values.
Thus ECG signal is compressed by using FFT technique.
Applications:-
• It finds application in hospitals, when a patient’s report is to be send to another doctor in prenomial place.
High Gain, Low Noise Instrumentation Amplifier Using Three Operational Amplif...IJEEE
This paper investigate the performance ofInstrumentation amplifier (INA) using three operationalAmplifier. The proposed circuit works for low input voltageequalised to the heart beat of the human being to analyses theECG (Biomedical application) response. The analyses ofGain, Bandwidth, Unity GBW, Phase margin and outputnoise for operational amplifier used in INA and For the INAGain, Bandwidth, output noise and power Dissipation areanalysed. The proposed circuit designed on UMC 180nmCMOS technology file and all the simulation done onCADENCE SPECTRE Simulator.
Instrumentation: Liquid and Gas Sensing (Design Conference 2013)Analog Devices, Inc.
This session focuses on liquid and gas sensing in instrumentation applications.
Liquid Sensing:
Visible light absorption spectroscopy and colorimetry are two fundamental tools used in chemical analysis. Most of these light-based systems use photodiodes as the light sensor, and require similar high input impedance signal chains. This session examines the different components of a photodiode amplifier signal chain, including a programmable gain transimpedance amplifier, a hardware lock-in amplifier, and a Σ-Δ ADC that can measure a sample and reference channel to greatly reduce any measurement error due to variations in intensity of the light source.
Gas Sensing:
Many industrial processes involve toxic compounds, and it is important to know when dangerous concentrations exist. Electrochemical sensors offer several advantages for instruments that detect or measure the concentration of toxic gases. This session will describe a portable toxic gas detector using an electrochemical sensor. The system presented here includes a potentiostat circuit to drive the sensor, as well as a transimpedance amplifier to take the very small output current from the sensor and translate it to a voltage that can take advantage of the full-scale input of an ADC.
P-Wave Related Disease Detection Using DWTIOSRJVSP
: ECG conveys information regarding the electrical function of the heart, by altering the shape of its constituent waves, namely the P, QRS, and T waves. ECG Feature Extraction plays a significant role in diagnosing most of the cardiac diseases. This paper focuses on detection of the P-wave, based on 12 lead standard ECG, which will be applied to the detection of patients prone to diseases. The ECG signal contains noise and that noise is removed using Bandpass filter. After elimination of noise, we detect QRS complex which help in detecting the P-Wave. P-wave morphology can be determined in leads II as monophasic and V1 as biphasic during sinus rhythm. DWT provides a value that helps in estimating features of the P-Wave. This detects the diseases that occur when the P-wave is abnormal. The method has been validated using ECG recordings of 250 patients with a wide variety of P-wave morphologies from Database
Distance measuring unit with zigbee protocol, Ultra sonic sensorAshok Raj
With Zigbee protocol, developed a distance measurement unit using an ultrasonic sensor, Arduino and X-bee trans-receiver for communication between displays and monitoring unit.
Software used: Arduino
A Wireless Physiological Monitoring System for Hyperbaric Oxygen ChamberIJRES Journal
This paper introduces a system which can monitor multi-physiological parameters in the hyperbaric oxygen chamber. The monitoring system was designed as a star wireless sensor network and the system’s transmission protocol based on the IEEE802.15.4 were programmed. The signals can be collected with the sensor network working under network synchronization. The system can be used to monitor physiological parameters such as blood pressure, pulse rate and temperature. A prototype of the monitoring system has been fabricated and extensively tested with very good results.
Biomedical Instrumentation Presentation on Infrared Emitter-Detector and Ardu...Redwan Islam
In this project, we measured human heart rate using IR emitter and detector, Arduino board and some other low cost component. We observed heart rate of some individuals with IR emitter and detector, Arduino Board and Processing 2.0 software, and attached the result in the report. We compared the cost of heart rate monitor that uses IR emitter and detector, and the one that uses pulse sensor.
Heart beat monitor using AT89S52 microcontrollerSushil Mishra
We , in this project are measuring the heart beat using the pulse oximetry logic.
The timer we have set for counting the heart beat is 30s.
There is a set point we can decide, after 30 s the heartbeat would be shown on the LCD along with a buzzer sound (if it exceeds the set point).
In this paper, an ATmega16 based system for vital signs recording using GSM is developed to measure patient’s
Heart Rate, Blood oxygen saturation percentage ,Body Temperature & also records ECG in real time. Nowadays people
are dying because of various health problems so a device will be designed to keep track on patient which should be easy
to use, portable, light weighted, small size so that it gives freedom of mobility for patient. The system is for home use by
patients that are not in critical condition but need to be periodically monitored by clinician. At any critical condition the
SMS is send to the doctor so that quick services can be provided.
Design of the Pulse Oximetry Measurement Circuit and Its Sensing System Based...IOSRJEEE
The pulse oximetry circuit and its sensing system is designed based on the standard CMOS technology of 0.18um. The reflection oxygen sensor is used to collect the pulse oximeter signal of human body, then the collected physiological signals are processed by the data processing circuit The data processing circuit is composed of two parts: the amplifying circuit and the band-pass filter circuit, and the pulse oximeter data processed by the data processing circuit is written into the tag through the SPI communication The RFID reader read the data in the RFID tag through wireless communication, and display the data . The experimental results show that the maximum error is ±1%. The maximum error of the pulse is ±1.9%. The stability and feasibility of pulse blood oxygen sensing system is demonstrated in this paper and it will have a good application prospect in the direction of wearable medical wisdom research
Design and development of electro optical system for acquisition of ppg signa...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
A sensor (also called detector) is a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an (today mostly electronic instrument.
1. Pulse Oximetry using Programmable Mixed Signal Array GreenPAK Device
By Ahmed Asim Ghouri 29th July, 2016
Introduction
Pulse oximetry is a simple non-invasive method of monitoring the percentage of hemoglobin
(Hb) which is saturated with oxygen. The pulse oximeter consists of a probe attached to the
patient's finger or ear lobe which is linked to a computerized unit. The unit displays the per-
centage of Hb saturated with oxygen together with an audible signal for each pulse beat, a
calculated heart rate and in some models, a graphical display of the blood flow past the
probe. Audible alarms which can be programmed by the user are provided.
The color of blood varies depending on how much oxygen it contains. A pulse oximeter
shines two beams of light through a finger (or earlobe etc.), one beam is red light (which you
can see when a pulse oximeter is used), one is infrared light (which you don't see). (Netter
T, 2004)
These two beams of light can let the pulse oximeter detect what color the arterial blood is
and it can then work out the oxygen saturation. However there are lots of other bits of a
finger which will absorb light (such as venous blood, bone, skin, muscle etc.), so to work out
the color of the arterial blood a pulse oximeter looks for the slight change in the overall color
caused by a beat of the heart pushing arterial blood into the finger.
This change in color is very small so pulse oximeters work best when there is a good strong
pulse in the finger when the probe is on. If the peak signal value is too low the measured
oxygen saturation may not be reliable and with lower signal peak value the pulse oximeter
will not be able to work, to acquire a strong signal output from the IR sensor pulse oximeter
increase the intensity of RED and IR LED’s in successive steps.
Oxygen Concentration
A Pulse-oximeter monitor displays the percentage of blood that is loaded with oxygen. More
specifically, it measures what percentage of hemoglobin (Tilakaratna, n.d.), the protein in
blood that carries oxygen, is loaded. Acceptable normal ranges for patients without pulmo-
nary pathology are from 95 to 99 percent. For a patient breathing room air at or near sea
2. level, an estimate of arterial pO2 can be made from the blood-oxygen monitor "saturation of
peripheral oxygen" (SpO2) reading.
Absorption of Red Light and Infra-red light (Twonsend, 2001)
A typical pulse oximeter utilizes an electronic processor and a pair of small light-emitting
diodes (LEDs) facing a photodiode through a translucent part of the patient's body, usually
a fingertip or an earlobe. One LED is red, with wavelength of 660 nm, and the other is infra-
red with a wavelength of 940 nm. Absorption of light at these wavelengths differs signifi-
cantly between blood loaded with oxygen and blood lacking oxygen. Oxygenated hemoglo-
bin absorbs more infrared light and allows more red light to pass through. Deoxygenated
hemoglobin allows more infrared light to pass through and absorbs more red light. The LEDs
sequence through their cycle of one on, then the other, then both off about thirty times per
second which allows the photodiode to respond to the red and infrared light separately and
also adjust for the ambient light baseline. (Pulse oximetry, n.d.) The amount of light that is
transmitted (in other words that is not absorbed) is measured, and separate normalized sig-
nals are produced for each wavelength. These signals fluctuate in time because the amount
of arterial blood that is present increases (literally pulses) with each heartbeat. By subtract-
ing the minimum transmitted light from the peak transmitted light in each wavelength, the
effects of other tissues is corrected for. The ratio of the red light measurement to the infrared
light measurement is then calculated by the processor (which represents the ratio of oxy-
genated hemoglobin to deoxygenated hemoglobin), and this ratio is then converted to
SpO2 by the processor via a lookup table based on the Beer–Lambert law. The hardware
and software to acquire SpO2 data will be included in the further extension of this application
note.
3. Pulse-oximeter Finger Probe
Signal Processing
Some initial signal processing is required when trying to extract oxygen concentration from
the signal coming from finger sensor. The calculations follow Beer-Lambert Law
(Matviyenko, 2011) to assess the percentage of the oxygenated blood. Mathematically given
as:
The figure 1 below shows how light is absorbed in the finger:
Figure 1 : Absorption of Light (Matviyenko, 2011)
There are some components which contribute to the absorption of light listed below :
1. Oxygenated Haemoglobin in the blood
2. De-oxygenated Haemoglobin
3. Absorption that is not from arterial blood
4. Optical attenuation due to scattering, geometric factors etc.
4. Figure 2 shows main block diagram of the Pulse Oximeter application using Green Pak’s
device SLG46140.
Figure 2 : Block Diagram of the Pulse Oximeter
The GreenPAK device will generate drive signals for both IR and RED LED’s, whereas ADC
within the device will sample IR Sensor output and send data serially out. As shown in the
figure 3, it will turn IR LED ON for 100 ms, while RED LED is off and then turn RED LED on
for the next 100ms and at the end of the cycle turn both IR and RED ON to acquire another
reading. Figure 3 shows the timing diagram of the POR (power On Reset) , ref Clock , IR
LED and RED LED drive signals and ADC data output.
Figure 3 : Timing waveform for IR and RED LED’s
5. To control the brightness of each LED, SLG46140 will produce a varying PWM. The average
value of voltage (and current) fed to the load is controlled by turning the switch between
supply and load on and off at a fast rate. The term duty cycle describes the proportion of 'on'
time to the regular interval or 'period' of time; a low duty cycle corresponds to low power,
because the power is off for most of the time. Duty cycle is expressed in percent, 100%
being fully on.
Figure 4 : PWM waveform
Both RED and IR LED’s brightness will be controlled using varying PWM to conserve energy
as this can be a portable battery powered device and also to determine which light intensity
is suitable for a certain type of finger. As shown in figure: 1, some portion of light source is
absorbed by the skin and muscle tissue in the finger.
6. Implementation with GreenPAK Designer
Figure 5 shows top level block diagram of the design that will perform two main functions
of the pulse oximetry i.e driving RED and IR LED with varying intensity and acquisition of
the IR sensor signal .
Figure 5 : SLG46140 implementation of Pulse Oximetry
7. Figure 6 shows the schematic of the SLG46140 internal connections for both PWM
generation and IR signal acquisition. Pin 6 has been configured as Analog input and
connects to PGA with a gain of x0.25, PGA’s output is connected to ADC. The serial data
output of ADC is connected to digital output pin 12, ADC interrupt signal is connected to PIN
12 and ADC sampling clock is connected to PIN 14 . All of these three i/o pins i.e PIN 12, 13
and 14 are configured to be Digital output, whereas PIN 6 is set to be Analog input. Figure
7 shows the setting for PGA and ADC for this application.
Figure 6 : SLG46140 GreenPAK Designer Schematic
8. Figure 7 : PGA and ADC Settings
The screen capture of FSM that controls the PWM can be seen in Figure 6. The 3-bit LUT0
is connected to PIN3, PIN5, which are configured as Digital in with Schmitt trigger with pull
up resistor 1MegΩ. Output of 3-bit LUT0 is connected to KEEP FSM1. When KEEP is HIGH,
Q will stay at its current value. The 2-bit LUT0 is configured as NAND. Output LED is
configured to be 1x Open Drain NMOS. PWM period is defined by the period of FSM0. If
button “+” is held high , "LED" output will generate PWM signal with changing duty cycle
from 256/256 to 1/256 (the LED brightness will go up). When button “-” is held at logic high,
"LED" output will generate PWM with changing duty cycle from 1/256 to 256/256 (the LED
brightness will go down). Refer to AN-1052 (Holod, 2014) for complete details about PWM
application for the SLG46140 device.
10. Figure 8 and 9 show setting for RC and LF Oscillator for this application, ADC reference
clock is the OUT0 output of the RC OSC which is pre divided by 2 and then divided by 12.
LF OSC output is divided by 16 and connected to LUT1 and to PIN11 i.e RED En output,
where LUT1 is set to output XOR output.
Figure 10 : LUT1 Setting
11. Hardware Design and Testing
Refer to figure 10 which basic arrangement of a Pulse Oximeter finger probe, where RED
and IR LED are embedded in to the upper lip of the finger clip and IR sensor is placed in the
lower lip.
Figure 10: Pulse Oximeter finger probe internal circuit diagram
Figure 11: Pulse Oximeter finger probe front end circuit
12. Figure 11 shows complete front end circuit for the finger probe, LM7805 and LM315 provide
a regulated DC output of +5.0V and +3.3V. RED and IR LED are connected to the collector
output of transistors 2N2222 each with series resistor of 220 ohm and a 3.3V Zener diode
in parallel, where base of T1 and T2 are fed with PWM1 and PWM2 from tri-state buffers.
RED En and IR En enable the buffers to transmit PWM waveform to the T1 and T2. IR
Sensor BPW34 is connected to +5.0V in reverse biased configuration with a 10K series
resistor and 100nf capacitor in parallel. Tri-stat buffers are used as a precaution to ensure
that PWM input from GreenPAK device to the base of T1 and T2 are at CMOS (i.e
maintaining +3.3V ) output.
Figure 12 : Output of IR Sensor when both RED and IR LED are ON
The figure 12 shows oscilloscope screen capture of the IR Sensor output from the front end
circuit, where its Vpp is 1.84mV the gain of PGA is set to 0.25 as ADC input should not
exceed 250mV . Figure 13, 14 and 15 show testing results of varying duty cycle of PWM
output when +ve input is kept at high refer to figure : 6 , it is the output of PIN 10 . To
decrement duty cycle –ve input i.e PIN 4 is connected to logic high. Figure 16 shows test
results of digital output PINs 9 and 11, the enable signals for RED and IR LED’s are 90
degree phase shifted relative to each other.
13. Figure 13 : PWM Output with 1% duty cycle
Figure 14 : PWM Output with 10% duty cycle
14. Figure 15 : PWM Output with 60% duty cycle
Figure 16 : RED and IR LED enable signals
15. Analogue to digital Conversion
Refer to figure 6 which shows schematic of SLG46140, the ADC portion consists of analogue
input pin no : 6 which is connected to PGA whose output is sampled by ADC. The two
interface signals from ADC are ADC interrupt connected to pin no : 13 and serial ADC data
to pin no : 12 as well as Clock at pin no : 14 .
Figure 17 : ADC Signals
Figure 17 shows screen shot of LogicStudio 16 (logic analyzer) of ADC signals, where D0
is the ADC interrupt signal, D1 is the ADC serial data and D2 is the clock. Figure 18 shows
the wiring of the bread board , implementing Front end circuit , whereas Figure 19 shows
the screen shot of the GreenPAK emulator . As an extension to this application note the
serial ADC data will be latched by a Master processor and real-time data will be displayed
on a LCD , thus verifying that correct data from ADC has been transmitted .
16. Figure 18 : Proto-board circuit of Front End Ckt shown in schematic of figure no : 11
Figure 19 : GreenPAK emulator
17. Extensions
This application note does not cover all aspects of information extraction processes involved
in Pulse Oximetry. It shows how SLG46140 can be used as a mixed signal device to perform
some basic functions required to acquire Heart rate and Oxygen concentration. Some signal
processing can be done to improve the output from the GreenPAK device if more resources
were available within the chip. GreenPAK devices are easy to configure and implement a
functionality, as no prior knowledge in any particular programming language is required, the
GreenPAK Designer is a user friendly tool. GreenPAK device SLG46140 can be used with
any Microcontroller or FPGA to act as a mixed signal front end device, because of their small
size and footprint these devices can be integrated into small form factor hardware.
SLG46140 has analog comparators, Programmable Amplifier and a ADC (Analog to Digital
converter) thus less component count and effort for the PCB designer to route and isolate
tracks. More serial interfaces can be added to SLG46140’s ADC such as SPI, I2C and UART
to interface its data output seamlessly to Master CPU. These devices are well suited to be
connected to various sensors and format the signals for further processing.
Conclusion
Implementing Pulse Oximetry using GreenPAK device proved to be simple yet low cost
front end solution. The small size and ease of programming these devices makes them
ideal for any application where mixed signal processing is required.
18. References
Holod, B. (2014, December 22). Silego . Retrieved from Silego Technology:
http://www.silego.com/products/355/312/AN-1052.html
Matviyenko, S. (2011, February 01). Sensing – Pulse Oximeter with PSoC® 1. AN2313. Cypress
Semiconductor.
Netter T, S. M. (2004). Signal Processing In A Low-PowerWearable Oximeter. BIOSIGNAL (p. 3).
Winterthur, Switzerland: Institute of Mechatronic Systems IMS.
Pulse oximetry. (n.d.). Retrieved from wikipedia: https://en.wikipedia.org/wiki/Pulse_oximetry
Tilakaratna, P. (n.d.). how equipment works. Retrieved from
https://www.howequipmentworks.com/pulse_oximeter/
Twonsend, D. N. (2001). Pulse Oximetry. Medical Electronics (p. 11). Michaelmas Term.