MC9S08LL16

Freescale Semiconductor Application Note Document Number : AN4025 Rev. 1, 4/2010 Implementing a Glucometer and Blood Pressure Monitor Medical Devices by: Roxana Suarez and Carlos Casillas RTAC Americas Guadalajara Mexico Contents 1 Introduction...........................................................1 2 Glucometers and Diabetes.....................................2 3 Blood Glucose Monitor.........................................4 4 Blood Pressure Monitor and Hypertension...........6 5 Blood Pressure Monitor .......................................7 6 Technology and Medical Devices ......................11 7 LCD Driver.........................................................11 8 Bluetooth Connectivity.......................................17 9 Micro SD Card....................................................20 10 Power Management.............................................24 11 Errors System......................................................25 12 Personal Healthcare Device Class and Medical USB Stack Applications...............................................25 13 User Guide..........................................................26 14 Conclusion...........................................................30 15 References...........................................................30 1 Introduction This document describes a combinational medical device designed to integrate both a low-end glucometer and a blood pressure monitor. Nowadays, people suffering from chronic degenerative diseases such as hypertension and diabetes can develop a plurimetabolic syndrome. This syndrome and both diseases in the same patient share some risk factors such as obesity, hypercholesterolemia, and atherosclerosis. Medical combinational devices target this new market and not only is power consumption a target, but bringing a better solution for disease control. This application note addresses medical devices implemented with Freescale technology. By using the MC9S08LL16 this device is energy efficient. It includes a Medical USB Stack programmed into the MC9S08JS16 for communication and the MPXV5050GP pressure sensor. A glucometer is a device for measuring levels of glucose concentration in the blood. This device is usually portable and is used at home for monitoring diabetic-patients. A blood pressure monitor is a device that detects systolic and diastolic blood pressure, heart rate, and mean arterial pressure for patients who suffer or are at risk of developing high blood pressure. © 2009 Freescale Semiconductor, Inc. Glucometers and Diabetes 2 Glucometers and Diabetes Diabetes is one of the most common diseases today. It is essential to produce glucometers whose one of many advantages is to empower diabetics to take care of themselves without the need to visit doctors. Glucometers help to detect and confirm hypoglycemia and infections. High blood sugar may also be a sign of infection or illness that needs to be treated. 2.1 Diabetes Fundamentals Diabetes mellitus commonly known as “ diabetes ” is a common health problem throughout the world. It prevents the body from producing enough insulin, does not produce insulin, produces defective insulin, or has resistance to the same. Insulin is a hormone produced in the pancreas. According to the World Health Organization statics, the global prevalence of diabetes mellitus is approximately 155 million people and expected to increase to 300 million in the year 2025. Medical Management of Diabetes and Heart Disease Book, Marcel Dekker Inc. Glucometry is a technique that obtains the value of glucose concentration in peripheral or central blood. These values expressed either in mgr/dl or mmol are important clinical values for metabolic disorders such as diabetes mellitus, denutrition, and other consequences like hyperosmolar coma, malabsorption syndrome, and most critical hypoglycemia. A glucometer and proper pharmaceutical treatment is fundamental for glycemic control of diabetic patients. At home, some glucometers include different kinds of strips to monitor other variables such as ketones which are produced when a patient is experiencing hyperglycemia. Figure 1 shows a general diagram of a blood pressure monitor. It shows different peripherals for communication between the user and the device. The most important part is the test strip, this is the sensor to collocate the blood and get a determined measurement with the analog-to-digital converter (ADC) of the microcontroller unit (MCU). The other peripherals depend on the designer. Figure 1. Blood glucose monitor block diagram 2.2 Glucose Sensors The first step to measure the glucose in the blood is to convert the glucose concentration into a voltage or current signal, this is possible with special sensor strips for amperometry. The sensor uses a platinum and silver electrode to form part of an electric circuit where hydrogen peroxide is electrolyzed. The hydrogen peroxide is produced as a result of the oxidation of glucose on a glucose oxide membrane. The current through the circuit provides a measurement of the concentration of hydrogen peroxide, giving the glucose concentration. Implementing a Glucometer and Blood Pressure Monitor Medical Devices, Rev. 1, 4/2010 2 Freescale Semiconductor, Inc. Glucometers and Diabetes Figure 2. Electrode reactions between glucose and gluconic acid The sensor used as a blood-glucose meter is based on a glucose oxide electrode. The glucose oxides were immobilized in a platinized activated carbon electrode. The enzyme electrode was used for amperometry determination by using an electrochemical detection of enzymically produced hydrogen peroxide. The sensor is composed of various electrodes; a glucose oxide membrane layer, a polyurethane film that is permeable by the glucose, oxygen, and hydrogen peroxide. 2.3 Amperometry Amperometry measures electric current between a pair of electrodes that are driving the electrolysis reaction. Oxygen diffuses through the membrane and a voltage is applied to the Pt electrode reducing O2 to H2 Figure 3. Test strip basic block diagram These reactive electrodes are amperometric type sensors that use a three electrode design. This approach is useful when using amperometric sensors due to the reliability of measuring voltage and current in the same chemical reaction. Three electrode models use a working electrode (WE), reference electrode (RE), and a counter electrode (CE). After this current is produced this must be changed to voltage for processing by the MCU. This action is performed by the transimpedance amplifier. Finally, the MCU detects and processes this signal with the ADC module. For a transimpedance amplifier and sensor designs for medical applications go to Medical Application User Guide at www.freescale.com. Implementing a Glucometer and Blood Pressure Monitor Medical Devices, Rev. 1, 4/2010 Freescale Semiconductor, Inc. 3 Blood Glucose Monitor Figure 4. Chip schematic Use an amperometric determination method with a constant potential of 0.3V used in the portable meter. The current response of the sensor is linear with a glucose concentration in the range of 5 to 30 mmol/ L and a fast response time of about 20 seconds. 3 Blood Glucose Monitor This section explains how to develop a medical device for measuring the blood glucose level. This device operates placing a relatively small drop of blood on a disposable test strip that interfaces with a digital meter. Within seconds the level of blood glucose is shown on the liquid crystal display (LCD). 3.1 Transimpedance Amplifier The transimpedance amplifier consists of an operational amplifier and a feedback resistor between the output and the negative input. The positive input can be connected to either GND or used for offset calibration. 3.2 Glucose Software Overview The voltage source is always at 3.3 V. To start taking ADC samples, the source voltage must go to 0.3 V. The connection between the source and the application contains a voltage regulator of 3.3 V. You can provide voltage to the system by using a 9 V battery. TakeSample function —The function configures the ADC module and starts conversion. It compares the ADC conversion obtained with Value1 which is 60. If the ADC conversion is lower than this value, the MCU goes into stop mode, and after 20 seconds sends an error message to the LCD. void TakeSample (void) { . . . ADC_Start(); Strip_CTRL =StripVoltage300mV; CountSec=0; ADC_Start_conversion (2); //0.3V Supply Drop=1; while(ADC_Get_Newconversion(2)