Walking Stick With Heart Attack Detection ECE 445 Helen Kim Spring 2005 Choon Lee Project 28
Introduction • Why did we choose this topic? • Create an equipment to be used in everyday’s life for a medical purpose • Obtain the basic idea from “Wireless Heart Attack Detector with GPS” of Fall 2004 • Most heart attack results from coronary artery disease (the restriction of blood flow to the heart) and it causes instant death of person ----”The Center for Disease Control”
Why did we choose this topic? (continued) • Help senior citizens who have health hazardous moment most often • Use a walking stick as the medium asking for medical help as well as the main unit of detection
Objective • Goals of Design: -The wireless heart attack detector captures abnormal heart beat signals. -The alert system on the walking stick warns the user to realize his health condition. -Bluetooth wireless emergency calling system calls for help at the moment of heart attack via mobile phone.
Objective (continued) • Benefits: • Electrocardiogram (ECG) signal transmitted wirelessly from the wrist to the main unit on the stick. This avoids the inconvenience of the attachment of the stick to the wrists. • Automatic wireless emergency calling system via Bluetooth module • Warning mode giving the users a chance to avoid the fatal moment actively
Original Design Review • Obtain ECG waveform from both wrists. • Transmit ECG waveform wirelessly from wrist to a receiver on the stick. • Microcontroller on the stick will run a heart attack algorithm to detect possible heart attack. • Microcontroller will make the user’s cell phone to call 911 if heart attack detected.
Electrodes Bluetooth Module (EB500) ECG Unit Javelin Stamp (microcontroller) A/D Converter Transmitter Receiver Block Diagram
Components and Functions • ECG Analog Circuitry – to obtain analog ECG waveform from wrists 1. Unity-Gain Buffer. As Impedance Transformer. Skin impedance is high and Op-Amp’s input impedance is infinity. 2. Differential Amplifier. Taking the difference between two bio signals from both wrists and output the ECG waveform with desired gain.
Components and Functions 3. Bandpass Filter Lower Cutoff Frequency – 0.9 Hz Upper Cutoff Frequency -105 Hz - This filter removes noise outside the frequency range of ECG waveform. - Without the filter, no recognizable ECG was obtained during testing.
Components and Functions • PIC16F877 as A/D Converter and RS232 1. A/D Conversion Analog ECG signal will be digitized into 8 bits (0 – 127). 2. RS232 -Parallel bits of ECG digital data will be translated into serial bits for transmission. -It is a standard for serial binary data interchange between a DTE (Data terminal equipment) and DCE (Data communication equipment)
Components and Functions • HP-3 Transmitter 1. The RS232 output of PIC16F877 will be fed into the input of HP transmitter. ***All the above components, ECG analog circuitry, PIC16F877 and HP-3 Transmitter will be worn on a wrist.
The following components will be installed on the walking stick. 1. HP-3 Receiver 2. Javelin Stamp microcontroller 3. EB500 Bluetooth Module
Components and Functions • HP-3 Receiver 1. The receiver will receive digital ECG waveform from wrist. 2. The receiver will then feed the digital signal to Javelin microcontroller.
Components and Functions • Javelin Stamp Microcontroller 1. Microcontroller will run an algorithm through the ECG data to detect heart attack symptoms.
Components and Functions • 2. Heart Attack Algorithm - Symptoms of Heart Attack Weak Amplitude, Irregular Heart Pulse and Widened QRS Pulse. - Checking Amplitude -A baseline is set up by averaging all the data points.
Components and Functions -Amplitude is considered weak if it is below 50% of the baseline. -Checking Irregular Heart Beat - normal pulse rate is between 35bpm and 200bpm - if pulse rate falls outside of this range, then heart attack symptom is detected.
Components and Functions -Checking Widened QRS Pulse - Normal pulse width should be less than 36ms.
Components and Functions • Alert Level - The failure of each of the three symptoms will raise the alert level. -The threshold of the alert level is set to 10. -If threshold is surpassed, emergency call will be activated.
Components and Functions • LEDs -Two LEDs will indicate the alert level. -First LED means low risk, which will be turned on for alert level between 4 and 6. -Second LED means high risk, for alert level between 7 and 9.
Components and Functions • EB500 Bluetooth Module -Javelin Stamp will send some commands to EB500 to set up a connection between the bluetooth module and the cell phone. -Bluetooth communication is nothing than just a wireless serial cable after the connection is set up.
Components and Functions • AT commands -AT commands direct a phone to dial (D), answer (A) and hang up (H). -Every AT command starts with “AT” (Attention). This is the command line prefix.
Components and Functions • -AT commands to make 911 call • “ATD911; \r” • “ATD2173335257; \r” (Calling lab)
Functional Testing • A/D Testing by inputting a known voltage level and checking the corresponding digital value. • 0.1V - 5 • 1.0V – 50 • 2.0V – 100 • 2.5V – 125 • 8 bits can only go up to 127 • The highest peak of ECG waveform from analog circuitry will be amplified to only 2.0V
Functional Testing • Collecting ECG waveforms -ECG Samples of team members -Notice that the amplitude is between 127 and -127 for 8 bits A/D.
Functional Testing • Heart Attack Algorithm Testing • One of the ECG samples shown was stored and was changed in terms of amplitude, rate and width. • Javelin Stamp was modified to run with this modified data. • Each of the three thresholds responded correspondingly.
Functional Testing • Bluetooth Communication & Lab Call -The communication worked properly and the lab phone rang properly.
Successes & Challenges Challenges Before Successes • Each component has to be tested and debugged individually before they were combined together. • TTL logic signal of PIC were captured by scope to test the functionality.
Successes & Challenges • - ECG waveforms were captured by Javelin Stamp to test the wireless communication between wrist and the stick. • -Suitable bluetooth module was selected carefully by reading data sheets to check certain commands to make sure that it is connectable to a cell phone.
Successes & Challenges • The notion of AT commands was obtained by surfing online technical forums. • AT commands were given by somebody met at a technical forum.
Test • Operation Temperature We chose the reasonable range of outer weather. • Test Range: -25°C to 50°C inside freezer and by hair dryer • Result: We could observe that the whole system behaved properly.
Test (continued) • Transmitter / Receiver For our design, we assume the user stays the range of area near to the stick. • Test range between wrist circuitry and the stick : ~40 ft The javelin still could capture the digital signal.
Recommendations • Better biosensors that reduce noise when hands are moving. • Better circuit design to reduce power consumption. • Lighter material for the wrist circuitry and the main unit on the stick.