Schematic descriptions


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Schematic descriptions

  2. 2. INTRODUCTION: We are designing a tele-medicine platform that can monitor a patient’s biometrics and transmit the data to a nearby physician. With the increasing cost of health care throughout the world, it is very important to provide general health care facilities to patients who need continuous monitoring by a doctor. To eliminate a patient’s need of going to the hospital on a regular basis for a regular check-up such as blood pressure and EKG and cut out on these expenses, we are designing a platform that would measure a patient’s biometrics and transmit the data to a web database. The nearest doctor can then access the data. A call center attendant who can provide emergency help or notify a hospital nearest to the patient can also access the data. The data will be transmitted using GSM technology. OBJECTIVES: Following biometrics of a patient are to be measured: 1. Blood Pressure 2. Pulse Oxi-meter 3. Peak flow meter 4. Temperature 5. Electrocardiograph 6. Pulse rate All the measurements would then be processed and sent onto a web server (or e-mail) that can be accessed from a call center. The data will also be available to the patient on an LCD. The data will be transmitted to the web server through cellular (GSM) technology. Once the data is received, the call center can call the patient to provide first aid and also contact a doctor in case of emergency. Benefits to end customers: 1. Immediate first aid available through call center attendant and a doctor in case of an emergency 2. Money and time saved. 3. Remote assistance for areas with no/limited medical facilities 4. Medical history of the patient stored in a server and accessible to the patient any time. 5. Complete check up unit available to patient anytime. Product features: 1. Uses ultra-low power micro-controllers. 2. Runs on three AA batteries. 3. Wirelessly transmits data using GSM technology. 4. GSM compatible with AT&T and T-mobile SIMcards. 5. Display of Measurement data. 6. Data encryption before transmission. 7. Accurate biometric measurement. 8. Automatic transmission of data once measurement is done.
  3. 3. BLOCK DIAGRAM DESCRIPTION: 1. BV513: BV513 is an interface board containing a PIC32MX340F512H. The microcontroller can be programmed using a USB connected to a Microsoft Windows PC. The PIC is interfaced with different I/O ports and serial ports. It is also interfaced with a micro SD card slot. The PIC contains 512K of program flash memory and 32K RAM. A block diagram of the BV513 board is shown below. During programming, the BV513 board can be powered using the USB. The PIC is programmed using the PIC32- Basic development kit available with the board. In general the language follows the conventional BASIC as found in other variants. Due to the unavailability of an external power source, we will design the board to run with a set of three AA battery cells connected to the USB once the programming is completed. The Micro SD card is interfaced to accept data serially. The BV513 outputs all of the PIC’s I/O via on board connectors. The deign is such that it can be mounted on a matrix type breadboard or used as a central platform for other peripherals. The main interface is Via USB employing a virtual COM port that can be driven as high as 2,000,000 Baud. All development work is done through this interface and the USB also provides power to the board.
  4. 4. The board comes with its own set of voltage regulators. The PIC and the USB operate on the 3V3 whereas the other peripherals operate on the 5V regulator. The PIC runs on an 80MHz clock and the default peripheral bus speed is 40 MHz. there is also a 32kHz RTC crystal controlled clock for system use. Schematic descriptions Pic 32: - Sampling rate on ECG determined the frequency required to distinguish the peak to peak voltages. 3 times the bandwidth is preferred. The peak to peak voltage is required to evaluate the heart rate. - Heart rate is evaluated from the ECG waveform by the formula: Let f denote the frequency of voltage spikes per second Heart rate=f(beats/sec)*(60sec/min)=f beats/min - Sampling on other biometric devices like blood pressure and temperature is not required as the data is unique and just the measured value. - 3V3 denotes the 3V USB to serial conversion on the schematic. - 3.3 is the reference voltage used at VADD. According to the PIC 32 datasheet preferred reference voltage is 2.3 to 3.6. GND and VSS are grounded. They form the common ground for the PIC, GSM module and the SD card. - The B port (RB0 – RB7) is used for the peripheral devices. These ports are data I/ O ports. In these ports the analog version of data comes from the peripheral devices. - Analog to Digital conversion of the peripheral signals are done as a first step. For the temperature the data is contained in the current, thus the A to D is done on the current while for the ECG, blood pressure the voltage is the one holding the information. SD Memory card: - The signals have 10k pull up resistors. - Detect and Write protect are controlled by the PIC via the pin at E port RE0 to make sure that the memory card is write active and detects data only when it is being sent to. We will program the PIC for this requirement. The pic will send a signal first and the memory card will be ready to take in the data. - Data is fed as serial input SDA2, the serial data input from the PIC into the DAT 1 of the memory card where the data is received. - G4 is connected via the resistor as a switch to denote whether the memory card is in slot or not. - GND and GND 1 are the grounds of the memory card and we choose a common ground as mentioned above and connect them. GSM : - GSM has a capacity of 5.5 V max for the VCC as per the datasheet. Hence, the same 3.3V is fed into the VCC which is a convenient voltage level
  5. 5. - Grounds are again common. - There are specific MIC gnd and MIC bias which are for the MIC ground and bias levels. We connect them to the GND and VCC respectively as we have already chosen a common ground and common source. - TxD is the port in the GSM which accepts serial data. We program the PIC to send the serial data through pin RD0 of the D port (O data pin). - The Reset of the GSM is attached with the Master Clear of the PIC 32 and so can be programmed accordingly for the clearing or resetting of the complete module.0 Blood Pressure To measure the blood pressure, air is first pumped into the cuff tied on the patient’s hand. Initially air is pumped above the systolic value or the maximum blood pressure value in a heartbeat. The stethoscope is used to detect the first pressure change which appears as a sound of the heartbeat. This continues until a certain pressure where this sound of the heartbeat is disappeared. Sounds heard on the first and the last time are the two readings of blood pressure a physician records. In our design we implement the blood pressure monitor using a pressure sensor MPX2050 instead of the stethoscope. The decision making of the first and the last sound heard is made by the PIC 32. As the person keeps pumping air into the cuff the pressure increases and likewise the output voltage drop supplied to the PIC increases. The desired point to stop pumping must be above the systolic pressure, and 160mmHg is a considerable value. The voltage corresponding to 160mmHg is 2.5V at the output supplied to the PIC. Once this voltage is reached the PIC tells the user to stop pumping air into the cuff. Cuff Pressur Band AC DC Pass couplin e Amplifier PIC3 Sensor Filter g 2 s stage
  6. 6. As the pumping of air into the cuff is stopped the pressure begins to drop and slowly reaches the systolic pressure. MPX2050 produces an oscillating voltage when this pressure is acquired. This is why there are two outputs one to denote the 2.5V threshold and the other to denote the beginning of oscillations. This is the first reading the PIC 32 records. Now as the pressure begins to drop, at one point the oscillating voltage is stopped and the voltage is dropped now back to DC but now at a lower value as the pressure is no longer 160mmHg. The point where the oscillations stop or the ac current is no longer received gives the second reading. Schematics: Schematic Description: 1) Pressure Transducer MPX 2050: The MPX 2050 is a piezoresistive pressure sensor from Motorola which provide a highly accurate linear voltage. It produces a linear temperature to pressure function. Following is the plot from the datasheet given in the Motorolla website:
  7. 7. It has two inputs for the sensor. One is connected with the cuff and the other is left open to sense how much the pressure is different from the air pressure. 2) DC Amplifier: The output voltage is very small in mV as shown in the above characteristic and hence we need an amplifier before connecting to the PIC. AD620 is used which is an ideal choice. A gain of about 200 will suffice. The Gain is determined by the formula (49.4kohm as specified in AD620 datasheet): Rg= (49.4kohm)/ (G – 1). Substituting, Rg=(49.4 * 10^3) / (200-1)=248.25 ohm. We use 240ohm in our circuit as it is readily available and serves us with a better gain.
  8. 8. 3) Band Pass Filter: Two active band pass filters are used as cascade. The reason of using two stages is that we will have a sharper frequency response cut off, SNR will be appreciably high and the overall gain will be higher. First stage: Low frequency cutoff= 1/(2*pi*(47uF)*(10k))= 0.34 Hz High frequency cutoff=1/(2*pi*(200nF)*(120k))=6.63 Hz Gain = - 120k/10k = -12 Second Stage: Low frequency cutoff= 1/ (2*pi*(47uF)*(10k))= 0.34 Hz High frequency cutoff=1/ (2*pi*(24nF)*(333k))=19.9 Hz Gain = - 333k/10k = -33.3 Thus, the overall gain in the two stage band pass filter is -12 * - 33.3=399.6. 4) AC coupling stage: It is necessary for the PIC to have 2.5V DC level. This is sufficed by the use of AC coupling stage:
  9. 9. Once we have the DC bias level it is easy to process AC signal on the PIC. Temperature: As temperature is one of the common features that are to be measured for any diagnostic test it cannot be neglected. The commonly accepted normal human body temperature is 98.6 F or 37 C. In our implementation for measuring temperature we use a thermistor device which is basically a thermal sensor – AD592. It is low cost but has a good precision in measurement.
  10. 10. Following is the block diagram: AD 592 Amplifier Thermist PIC3 or 2 The Amplifier is needed as the current produced by the thermistor is in micro Amps. It scales its output as 1uA/K. Schematics: Schematic Description: 1) AD592: It has a wide range of temperature -25C to 105C and thus as our normal body temperature (37 C) comes comfortably in that range, AD 592 suits are requirement. It basically gives an output current proportional to temperature. The range of operation is also high from 4V
  11. 11. to 30V. To consider voltage fluctuations we have chosen 5V as our Vcc for the AD 592. Following is the plot from the datasheet to show the output current response with temperature 2) Amplifier: As mentioned before the output current is in uA, thus we need an amplifier before we send the signal to the PIC. A simple non inverting amplifier is used for the operation which provides gain, G= ((100K + 10K) / 10K) = 11 which will suffice our requirement. Opamp used is dual LM 747. Calibration: As per the graph and scaling after the amplifier the calibration is done first on room temperature and the offset is added. As the graph is linear the offset will be added to other values. All calculations done in the PIC after AtoD conversion. Ethical Considerations
  12. 12. As a body measurement device accuracy is important and a must. Say a healthy patient makes a regular check up and finds an unusual ECG curve there will be a case of panic and hence clearly violates the ethical rules on the product. The accuracy and calibrations on our devices are two important constraints and great care must be taken if there is a circuit break or fault on a device. Secondly, all the measurements are made on the individual. So, great care is to be taken to protect the patient from unwarned electric shocks. As an ethical consideration the patient must be informed to prevent contact from other electrical surroundings while measurement is in progress. Electrical sensors are used in almost all peripherals and care must be taken so that patient is protected from skin infections. Ag- AgCL electrodes are directly placed on the hands of the user for measuring ECG. Thus, along with the product a separate information page must be attached so as to what first aid is to be given if there is any health concerns formed because of the products. As the patient is the one measuring there should be a simple and clear directions page also provided as the patient must be able to measure his body characteristics. It is important to abide the ethical rules especially in a product like ours which is related directly to the health of the user. Costs Analysis: COST Analysis: • Labor: Dream Salary: $50/hr $50/hr × 20 hr/week × 10 weeks × 3 people = $30000 • Parts Platform:
  13. 13. Part Quantity Unit Price Sub total Bv513 1 $60 $60 GSM862 1 $80 $80 /RWC001.htm AA batteries (16 units) 1 $9.99 $9.99 Subtotal $149.99 The biomedical instruments: EKG: Part Quantity Unit Price Sub total Ag-AgCl Electrodes 1 $45.00 $45.00 (reusable) Subtotal $45.00 Pulse Oximeter and Peak Flow Meter: Part Quantity Unit Price Sub total Infrared LED 2 $1.99 $3.98 product/index.jsp? productId=2062565 Infrared Phototransistor 2 $1.59 $3.18 product/index.jsp? productId=2049724&CAWEL AID=107592744 PSoC 1 $5.95 $5.95 Sub total $13.11 Blood pressure Part Quantity Unit Price Sub total Blood Pressure pad 1 $4 4 Temperature Part Quantity Unit Price Sub total Thermometer 1 $2 2
  14. 14. Grand Total : Labor + Sum of all sub totals = $30000 + $149.99+ $45.00+ $13.11+$4+$2 = $30214.1 PIC32 Programming: The PIC32 will detect the peripheral connected to it and will run a sub-routine for the analysis of the measured data. Once the device is switched on, a main loop runs that initializes all the required peripherals and waits for a peripheral to be connected. Any peripheral connected can be detected using software. Once a peripheral is connected and the data measured, the PIC32 processes it according to their specific subroutines. A button can be used to tell the controller when the desired peripherals have been used. The data is then encrypted dynamically. Overview: STA RT Initialize ports and peripherals. Store Call to SD card. subrouti Wait.
  15. 15. Clear memory. Is peripher al Is A “Don A e” Wait. butto Receive date and time Ask for person’s Display data on LCD. Encrypt all Save data to Is powe r Send data to e- mail through Stop.