Design Scheme of Medical Monitoring Device Integrated with GPS System

With the growing demographic shift towards an aging population, the demand for comprehensive care has increased significantly. However, the fast-paced nature of modern life often results in neglecting the necessary attention and support for these vulnerable groups. To address this challenge effectively, the integration of a GPS system into medical monitoring equipment becomes imperative to prevent incidents of individuals getting lost or disoriented.

The Global Positioning System (GPS), developed by the United States during the 1970s, represents a significant technological advancement achieved through a 20-year-long endeavor, involving a staggering investment of 20 billion U.S. dollars. Its widespread adoption and utilization have been notable characteristics of this navigation system.

In this article, TechSparks will present a design scheme for medical monitoring equipment that seamlessly incorporates GPS technology. The proposed device primarily consists of a single-chip microcomputer control module and a GPS receiving module, specifically tailored to address the requirements of outdoor caregiving scenarios.

Table of Contents

Device Hardware Design

MCU Control Module

By expanding the peripheral circuitry, we have successfully implemented the collection of physiological parameter data, keyboard operation, LCD display of physiological parameters, and automatic alarm functionalities. For the LCD display, we have opted for the G191 liquid crystal module, which boasts a resolution of 192×128 dots. Each dot measures 0.33×0.33mm, with a dot pitch of 0.04mm. The driving power required for the LCD module is +5V and -20V.

To control and facilitate the display of information on the LCD screen, we have employed the SED1335 LCD controller. This controller is responsible for receiving a diverse range of instructions and data from the control module, and generating the necessary timing signals to drive and showcase the content on the LCD display. The SED1335 is equipped with robust software functionality and possesses its own data RAM, which it can autonomously manage. This data RAM includes a designated cache area that enables efficient display management for our convenience.

SCM control module circuit

GPS Receiver Module

The primary function of the GPS receiving module is to receive data from GPS satellites, which constitutes the space component of the system. The received data is then transmitted to the single-chip microcomputer control module in real-time through the UART serial port.

During the design process, thorough analysis and comparison led us to select the GR-85 serial port GPS receiver. The GR-85 receiver demonstrates unique advantages in terms of signal capture and accuracy. Notably, it exhibits a remarkable signal recapture time of just 100ms and achieves a minimum speed update rate of 1s.

The GR-85 receiving module adopts a serial communication mode, with the following defined data format: 9600b/s baud rate, 8 data bits, 1 stop bit, and non-polarity output. In terms of protocol support, the GR-85 receiver is compatible with six types of NMEA-0183 protocol information: GGA, GLL, GSA, GSV, RMC, and VTG. These protocols differ in the specific information they provide to users. For instance, the RMC format includes speed information, whereas other formats may not. The designer can select the desired information format based on the project’s requirements. For this particular experiment, we have opted to utilize the RMC format.

The table below presents an overview of the pins associated with the GPS receiving module. The primary communication channel between the receiving module and the microcontroller is established through the TXA pin.

PinPin NameFunction Description
1VCC 5V+3.5~5.5V DC power input
2TXASerial Data output port A
3RXASerial Data output port A
4RXBSerial Data output port B
5GNDPower ground
6TIMEMARK1PPS Time mark output

System Software Design

When the GPS receiving board is powered on and in the working state, it continuously transmits GPS navigation and positioning information, which is received and processed by the single-chip system through the serial port. To effectively extract the GPS information, a defined frame structure is necessary. The data frame consists of a frame header, frame tail, and intra-frame data. Each frame concludes with a carriage return and line feed, indicating the end of the frame.

During the data frame processing, the first step is to identify the frame header and then extract the required data from the frame. Since the data segments within the frame are delimited by commas, the received data is typically examined to determine if it begins with the ASCII code “$”, indicating a frame header. Once the frame header type is identified, the processing continues by determining the current parameter being read based on the number of commas (‘,’). The corresponding extraction and storage operations are then performed accordingly. In our system, we utilize the interrupt method to obtain GPS data, ensuring timely and efficient data acquisition.

To store the received and processed time, longitude, and latitude data, a reserved space in the memory is allocated. Specifically, the memory addresses 3BH-5FH are designated for storing the received data, including time, longitude, and latitude. Additionally, addresses 6BH-7FH are utilized to store the processed data, comprising time, longitude, and latitude information. This organization facilitates convenient retrieval and utilization of the GPS data within the system.

The GPS data output format is as follows:

$GPRMC, <1>, <2>, <3>, <4>, <5>, <6>, <7>, <8>, <9>, <10>, <11>*HH. Format explanation:

  • <1> Current Greenwich Mean Time (GMT) position, formatted as hhmmss.
  • <2> Status: A indicates a valid position, and V indicates a warning of non-valid reception, i.e., fewer than 3 satellites in view.
  • <3> Latitude, formatted as ddmm.mmmm.
  • <4> Hemisphere indicator: N for north hemisphere, S for south hemisphere.
  • <5> Longitude, formatted as dddmm.mmmm.
  • <6> Hemisphere indicator: E for east hemisphere, W for west hemisphere.
  • <7> Speed over ground from GPS receiver on the surface.
  • <8> Course over ground, ranging from 000.0 to 359.9.
  • <9> Date, formatted as ddmmyy.
  • <10> Magnetic variation.
  • <11> Magnetic variation direction, either E or W.

Example output: $GPRMC,161229.487, A,3723.2475, N,12158.3416, W,0.13,309.62,120598,, *10

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