The COVID-19 pandemic has shaken everyone’s life to an extent never imagined in this era. Infected patients need to be continuously monitored for body temperature, heart rate, respiratory rate, blood oxygen saturation levels (SpO2). If the patient can be monitored remotely, the attending caregiver’s exposure can be dramatically reduced. Renesas has come up with a low-cost, slim-profile, turnkey Medical Patch reference design (see Figure 1) to solve this problem. It is a wireless patch that collects patient information and transmits it to any android phone over Bluetooth for continuous monitoring, limiting exposure to the patient.
The Medical Patch is made with flexible PCB and can be used on the forehead, arm or wrist. The ZSSC3230 temperature sensor IC is located on the backside so it can be in contact with skin for continuous temperature monitoring. The OB1203 bio-sensing IC is on the top side so it is easily accessible for a finger touch. In order to prolong battery life, biovitals such as heart rate, respiratory rate and SpO2 are monitored when a finger is placed on this IC. The patch uses a slim rechargeable flexi pouch Li-ion battery and the ISL9205 USB charger IC to recharge the battery so that it can be reused after proper sanitation.
The central processor of the patch is a low power 32-bit RX23W MCU which has a built in 12-bit A/D converter and is compatible with Bluetooth 5.0. It also supports several other communication interfaces such as USB 2.0 host/OTG, I2C and RSPI. The RX23W MCU collects temperature and biovital data from the sensors, processes the data and sends it over to an android phone through Bluetooth. The RX23W can also be flashed via USB during the development phase.
The two main sensors on this design are the ZSSC3230 and OB1203. ZSSC3230 is a signal conditioner IC with an internal auto-compensated temperature sensor which is used for measuring the human body temperature when in contact with the skin. OB1203 is a sensor module with a proximity sensor and a highly accurate photoplethysmography sensor (PPG). It has an integrated averaging function for high signal-to-noise ratio (SNR). The OB1203 can activate data collection of biovitals once a finger is placed on the sensor. Data collection stops once the finger is removed. The rate of data collection for both temperature and the biovitals speed up once the finger is in contact with the OB1203.
The ISL9205 Li-ion battery charger IC charges the flexible pouch battery per the standard Li-ion charge profile, i.e. constant current phase followed by a constant voltage phase. It has an integrated pass element that feeds directly to the MCU as well as charging the battery when an external USB cable is connected to the micro USB port on the patch. An ISL9021A LDO regulates the voltage supply from the battery to the MCU with low IQ, low noise and high PSRR.
The Android app for this medical patch allows the user to monitor the temperature, heart rate, SpO2, and respiration rate data real-time, in addition to providing battery status and system health checks. The interval rate for temperature data collection (when the finger is not placed on the biosensor) can be updated using the drop-down option in the app.
With this solution, Renesas provides a cost-effective, reusable, slim-profile, Bluetooth-enabled medical patch for remote patient monitoring including complete hardware and software assistance to accelerate their development.
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