A detailed explanation of a GSM-based telemedicine automatic call system

With the increasing pressure of survival and the aging of our society, the "empty nest" of elderly families has become a trend of social development. When empty-nesters encounter sudden illnesses such as heart disease and hypertension, they are often accompanied by symptoms such as confusion, incapacity, and falls. In most cases, patients are unable to complete the call for help by themselves, and often miss the best time for rescue, resulting in adverse consequences. To address this problem, this paper designs a GSM-based telemedicine automatic call for help system. The system has the advantages of easy portability, high reliability, and long transmission distance, and can solve the problem of medical assistance for empty-nesters.

1 System Description

The GSM-based telemedicine automatic call system consists of multiple slave stations and a master station, and its network structure is shown in Figure 1. The slave station system consists of several medical monitoring devices, controllers, and GSM modules to detect and wirelessly transmit vital signs. The master station communicates with the slave station through the GSM module and analyzes the relevant data received to provide reference for subsequent medical rescue.

The slave system carried by the user will periodically wake up the medical monitoring equipment to detect the user's vital signs. The slave controller will compare the collected data with the preset normal vital sign values. Once it exceeds the normal range, the slave controller will send the user code (used to distinguish different users) and the current vital sign value to the master station (medical institution) through the GSM module, and send an early warning message to the user's relatives' mobile phones. The master station (medical institution) can call up the user's previous medical records based on the user code and formulate a corresponding rescue plan based on the current vital sign values.

2 System Hardware Design

The slave system usually consists of an electronic blood pressure monitor, a fall detection module, a GSM module and a microprocessor ( CPU ). The master system consists of a GSM module, a microprocessor (CPU), a display and alarm circuit (it can also be connected to a computer through a serial port module). The system hardware block diagram is shown in Figure 2.

Medical monitoring equipment can be reasonably selected according to the actual situation of the monitored object. This article focuses on common heart diseases and hypertension among the elderly, so only electronic blood pressure monitors and fall detection modules are selected. At the same time, in order to reduce energy consumption and reduce the frequency of replacing slave batteries, the MSP430 series ultra-low power microprocessor is used.

2.1  Wireless Communication Module

The wireless data transmission module TC35 from Siemens is used , which can reliably realize data, voice transmission and short message services. The module integrates RF circuit and baseband, and the module operating voltage is 3.3~5.5 V. It can work in two frequency bands of 900 MHz and 1 800 MHz. It provides users with a standard AT command interface to facilitate user application development and design. The module also provides an RS 232 data interface, which can easily communicate with the microcontroller via serial port.

2.2 Microprocessor and GSM interface connection

The microprocessor in this system uses the MSP430 series single-chip microcomputer. This series of single-chip microcomputer is an ultra-low power mixed signal controller that integrates a wealth of on-chip peripherals, which can minimize the complexity of the system circuit and reduce the power consumption and volume of the system.

The connection between the microcontroller and the GSM module is shown in Figure 3. The microcontroller and the GSM module are connected after level conversion through the serial port module MAX232 (MAX232 has driving capability and no external driving circuit is required). It should be noted that the master station and the slave station can communicate bidirectionally, and the slave stations are distinguished by the user address code. Slaves cannot communicate directly with each other.

2.3 Fall Detection Module

This system uses the GY-29-ADXL345 digital acceleration module to implement fall detection. The core of this module is the ultra-low power 3-axis accelerometer ADXL345, which has a measurement range of ±16 g and digital output data in 16-bit two's complement format, which can be accessed through the S PI or I2C digital interface. It can measure static gravity acceleration in tilt detection applications, and can also measure dynamic acceleration caused by motion or impact, with extremely high resolution, capable of measuring tilt angle changes of less than 1.0°.

The basic principle of fall detection is to obtain information about the user's body posture changes by measuring the acceleration changes in three orthogonal directions during the movement of the user carrying the module, thereby determining whether the user has fallen.

The resultant acceleration of a human body falling down due to weightlessness in three orthogonal directions

, and the duration is proportional to the height of the fall (the harmfulness of the fall can be judged accordingly). After a human body falls, it generally remains in a short state of stillness (if a coma is caused by a fall, the stillness may last longer). At the same time, once a human body falls, its current posture and the posture at the previous moment will change greatly in a short period of time. In this system, whether a fall has occurred is judged based on the current synthetic acceleration value and the change between the current posture and the posture at the previous moment; the harmfulness of the fall is judged based on the duration of the synthetic acceleration being less than lg and the time the human body remains in a still state.

2.4 Vital Signs Monitoring

Considering the common heart disease and hypertension in the elderly, this system uses the PAL-901 wrist electronic blood pressure monitor to monitor vital signs. The blood pressure monitor can measure heart rate, high pressure and low pressure. The measured data can be output through the serial port. It sends 6 bytes of data at a time, with a transmission rate of 19,200 bit/s and a level voltage of 2.8 V. In addition, the blood pressure monitor is small in size and powered by dry batteries, making it very convenient to carry.

3 System Software Design

3.1 Communication Protocol

During the wireless transmission process, due to factors such as weather conditions, interference and noise, the wireless communication between the slave station and the master station often results in the loss of transmission frames or data transmission errors (bit errors). In order to ensure the reliability of transmission, a corresponding communication protocol needs to be formulated.

The GSM transmission data frame structure used in this system consists of a frame header, user address code, fall identification, vital sign data, and CRC check. The GSM transmission data frame structure is shown in Figure 4.

In practical applications, the probability of the data generated by noise being 1111111100000000 is very low, so the data frame is sent with 0xFF and 0x00 as the frame header to avoid erroneous data reception. A byte address encoding is used to distinguish different user slave systems. Data error detection uses CRC check. After the receiving end detects 0xFF and 0x00 bytes, it indicates that the received data frame is valid. If the CRC check of the frame is correct, it means that the reception is correct, otherwise it means that the frame transmission is wrong and the frame is discarded.

3.2 Program Flow

The program flow of the GSM-based telemedicine automatic call system is shown in Figures 5 and 6.

The slave system periodically wakes up the electronic blood pressure monitor to detect the user's vital signs and compares the collected data with the pre-set normal values. Once it exceeds the normal range, the user code and current vital sign values ​​are sent to the master station (medical institution) through the GSM module, and an early warning message is sent to the user's relatives' mobile phones. After receiving the data, the master station verifies the validity and reliability of the data. After verification, an alarm is issued and the user code and vital sign values ​​are displayed.

4 Conclusion

This paper designs a GSM-based telemedicine automatic call system. The system uses an acceleration sensor to measure the signal when falling, and proposes an accidental fall detection algorithm. The electronic blood pressure monitor monitors the user's vital signs, and uses the GSM wireless communication module for data transmission and alarm. It has the advantages of easy portability, high reliability, and long transmission distance, and can solve the medical assistance problem of empty-nest elderly people to a certain extent.