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Date: 16-12-14

Pulse Oximeter design using Dynamic NFC/RFID

By Raunaque Quaiser, Alok Mittal, and Neha Kochhar STMicroelectronics

The advancements in technology and connectivity open up previously unexplored avenues in the field of personal health monitoring. It is indeed true that ‘prevention is better than cure’. But In today’s fast paced and busy lifestyle, it often becomes difficult to take out time for frequent health checkups. An early detection of any medical condition can result in timely preventive action and remediation. This is where portable healthcare solutions can make a meaningful impact by providing us the ability to monitor our health related parameters easily. These portable solutions can be connected to Smartphones for sharing one’s health parameters with Health Consultants and Hospitals on a secure network. The Health Consultant and Hospitals can recommend additional tests or schedule an appointment with the relevant specialist if any discrepancy is detected. The complete solution opens the concept of Telehealth as shown in Figure 1.

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Figure 1: Telehealth eco-system

In this article, we talk about Pulse Oximeter design using Dynamic NFC/RFID (Near Field Communication /Radio Frequency Identification)tag. NFC tag used in healthcare designs provides additional features using Smartphones such as data acquisition and management.

Pulse Oximeter: It allows the user to measure SpO2 (Saturation of Peripheral Oxygen) and Heart rate non-invasively. SpO2 is basically a measure of the blood’s capability to carry oxygen to the remotest part of the body.This measurement is important for high altitude mountain climbers, athletes and people suffering from anemia.

NFC:NFC (Near Field Communication)isan RFID (Radio Frequency Identification) basedwireless communication technology commonly available in many Smartphones. The term ‘near field’ signifies a working distance of less than 4-5 cms. There are different RFID standards available for different applications such as animal tagging (ISO 11784/ISO 11785), item management (ISO/IEC18000), freight containers (ISO 23389), etc. STMicroelectronics Dynamic NFC/RFID tag (M24LRxxE) features I2C as well as NFC interface is compatible with ISO 15693 RFID standard. The ISO15693 is one of the prominent standards for NFC interface and has the added advantage of being readable from a greater distance as compared to other proximity cards. It operates at a carrier frequency of 13.56 MHz with data rate ranging from 106 Kbit/s to 424 Kbit/s.

ST Android App: STMicroelectronics had developed a free android application called ‘ST Health Care’ for NFC enabled Smartphone. This application allows the user to share their data via Internet, Bluetooth and SMS. The data can also be uploaded on Microsoft HealthVault account. This allows the health data to be available on internet and can be accessed by any authorized person at any time.
This patient-centric concept of bringing the healthcare from the hospital to the patient at home is helping people to overcome the health challenges and improve quality of life.

Pulse Oximeter Hardware Design: Pulse Oximeter hardware block diagram as shown in Figure 2is a portable battery operated design based on STM32L. The on-chip USB interface, 12 bit ADC/DAC (Analog to Digital Converter/Digital to Analog Converter) and integrated RTC (Real Time Clock) with its low power consumption makes the STM32L ideally suited for this application. Analog Front End comprises TSV612A rail to rail input/output CMOS op-amp with low input bias current (1pA typically). The low input bias current op-amp is critical for accuracy when used as a trans-impedance amplifier to convert photodiode current into voltage. The internal ADC and DAC are used to measure the conditioned sensor output and to remove DC offset respectively. MCU converts the sensor data into SpO2 and Heart rate information and displays it on a 128x64 OLED (Organic Light Emitting Diode) display.

Pulse oximeter design

Figure 2: Hardware Block Diagram

Read the full article at http://www.eeherald.com/section/design-guide/stoximeter.pdf

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