Multi-parameter monitoring intelligent clothing system

With the rapid development of sensor technology, material technology and wireless communication technology, the method of combining medical monitoring equipment with clothing can better meet people's needs.

This paper proposes a wearable multi-parameter monitoring intelligent clothing system, which organically combines sensors, fabric cables and flexible circuit boards into clothing, realizing dynamic and collaborative monitoring of multiple physiological parameters in daily life and working environments. It has the functions of physiological signal detection and signal feature extraction, and uses Bluetooth technology to complete data backup for further analysis. It can also use communication devices with Bluetooth function to realize functions such as remote medical services.

1 System Hardware Composition

The principle of the Bluetooth smart clothing system is shown in Figure 1. The system consists of a battery module, a sensor, a flexible circuit board, an electronic fabric, a central processing unit, and a Bluetooth module. The CPU uses the ADμC7024 processor based on the ARM7TDMI core of ADI. The ADμC7024 has excellent processing capabilities, integrates many on-chip peripheral devices, and has low power consumption, which is fully qualified for the current application of this system. This system uses sensors to non-invasively collect various vital signs parameters of the human body. The processor performs soft processing on the collected signals and can calculate information such as body temperature, heart rate, and blood pressure. And the information is backed up to mobile phones, computers, and other devices with built-in Bluetooth through the Bluetooth module. The system can send an alarm signal when the physical condition is abnormal. The system can also support remote medical services through forwarding.

1.1 Monitoring Sensors

The sensor is responsible for measuring the heart rate, body temperature and other vital signs. Considering the wearable characteristics of this system, in terms of sensor selection, try to choose integrated, sensitive and accurate products, which can not only reduce the area of ​​the system circuit, facilitate wear, but also improve the stability and reliability of the system.

The blood pressure acquisition module uses the MPXV5050GP piezoelectric sensor produced by Freescal, which is placed on the inner side of the elbow joint in the middle of the sleeve. This can directly convert the pressure of arterial blood on the blood vessel wall into an output electrical signal. The specific circuit is shown in Figure 2. The sensor uses ion implantation technology, and integrates amplifiers, filters and other signal processing unit circuits internally. Only a few components are needed externally to work. The amplified and shaped electrical signal is output at the output end, so the output end of the sensor is directly connected to the 12-bit ADC integrated in the ADμC7024 for analog-to-digital conversion. The blood pressure value is then obtained through software processing.

PVDF piezoelectric film has the characteristics of light weight, soft texture, good durability, and large dynamic range of piezoelectric response. The use of multi-layer contact piezoelectric film sensors to measure heart rate can reduce interference signals. The heart rate acquisition module uses the HK-2000H integrated digital pulse sensor, which is placed on the left chest of the clothing to measure the heart rate. HK-2000H integrates PVDF piezoelectric film, high-sensitivity temperature compensation elements, temperature sensing elements, program-controlled amplifier circuits, signal conditioning circuits, filter circuits, and A/D conversion circuits. Integration avoids the disadvantage of using discrete components to design circuits that occupy a large area. The schematic diagram is shown in Figure 3. The HK-2000H integrated digital pulse sensor uses a USB port output, and its output can be easily processed by software.

The body temperature acquisition module uses the Maxim analog temperature sensor MAX6612 to detect body surface temperature. MAX6612 uses a 5-pin SC70 package, with a maximum operating current of only 35μA. It has the characteristics of low power consumption, high accuracy, and small size. The ADC circuit is optimized and is suitable for the application of this system. The specific body temperature acquisition circuit is shown in Figure 4.

The relationship between the MAX6612 output amplitude and the measured temperature satisfies the expression

The measured output electrical signal is converted to digital by the 12-bit successive approximation ADC on the ADμC7024 processor. The conversion result is stored in the register ADCDAT0. The lowest bit of the ADC status register ADCSTA can be used to check whether the ADC conversion is completed. When the ADC conversion is completed, the lowest bit is set. By reading the value in the register ADCDAT0 and then using software, the measured body surface temperature is obtained according to the above algorithm.

1.2 Flexible Circuit Board

Considering the comfort of wearing clothing, while not affecting the processing of vital signs data, the design of the main board adopts a flexible circuit board. The circuit board uses polyimide or polyester film as the substrate, can withstand multiple bending, folding and winding, and has good heat dissipation performance. Combining it with electronic fabrics can easily distribute the sensor network throughout the body, which has little impact on the comfort of clothing and is conducive to the collection of various vital signs data.

1.3 Electronic fabrics

In order to obtain sensor data without affecting the wearing comfort as much as possible, this system uses the method of weaving metal wires into traditional fabrics to make electronic fabrics to achieve electrical connections between the modules in the clothing. This can not only protect the metal wires and reduce the discomfort of the wearer, but also facilitate the transmission of the data collected by the sensor to the processor for processing. [page]

1.4 Bluetooth Module

This system uses a Bluetooth module to achieve data exchange with external devices with built-in Bluetooth functions. In order to reduce the system size, reduce the system quality and reduce power consumption, this Bluetooth module adopts a Class-2 design scheme, USB output, and a transmission distance of 10 m. It supports Bluetooth 2.0 protocol to meet the needs of the system. The Bluetooth chip uses CSR's BC417413, and the chip integrates 8 MB of flash memory, which mainly stores the software of the baseband, link management layer and host control interface, and also includes some APIs for configuring the chip. The front-end RF bandpass filter uses MDR771F-CSR-T, and the balun uses TDK's HHM-1517 to complete the conversion between the system's differential RF signal and the antenna input and output signal. The schematic diagram of the specific design scheme is shown in Figure 5.

1.5 External expansion function

This system supports external expansion of system functions. According to the actual needs of patients with diabetes and hypertension, blood sugar and blood oxygen measurement modules can be installed to perform non-invasive and continuous monitoring of blood sugar and blood oxygen, etc., so that the wearer can measure at any time, which is convenient and easy to operate.

2 Software Design

The system software includes a wearable monitor part and an external device part.

2.1 Wearable Monitor Software

The wearable monitor can work in two modes: one is the heart rate collection mode, and the other is the full collection mode. The program flowchart is shown in Figure 6. When working in the heart rate collection mode, the wearable monitor monitors the wearer's heart rate in real time, and when the heart rate is less than a certain critical point, it sends an alarm signal to remind the wearer to pay attention, and at the same time sends the heart rate data to the external device via Bluetooth. This mode can reduce power consumption and extend the battery life. After receiving the command sent by the external device, the wearable monitor works in the full collection mode, at this time, all vital sign parameter data supported by the wearable detector are collected and transmitted to the external device through the Bluetooth module.

2.2 External device software

The software flow chart of the external device is shown in Figure 7.

The external device can remotely control the wearable monitor to work in the full-item collection mode, and display the various physiological indicators collected by the wearable monitor on the terminal screen in real time and save them for later viewing. If necessary, the collected data can be sent to the remote doctor through the wireless network and the Internet network to achieve remote monitoring. When the user's key physiological indicators are less than or greater than a certain critical point, the external device can send the collected data and GPS information to the pre-set emergency contact in the form of text messages and call this number, ensuring that the emergency contact can know the user's physical condition at the first time, take rescue measures in time, and protect the wearer's life safety. It is suitable for people with sudden heart disease.

3 Summary and Outlook

A smart clothing system for life monitoring is proposed and designed, which can select the appropriate working mode according to the needs of the user. At the same time, the system uses Bluetooth technology to network external devices such as the human body, smart phones and computers, which can back up the collected vital signs data and facilitate the development of remote medical services.