Design of MCU in heart rate monitoring system based on Atmega64L

1 Introduction

According to the exercise heart rate, the exercise intensity level can be accurately divided. Through the intelligent judgment of the monitored heart rate according to the divided level by the single chip microcomputer, the training intensity can be monitored in real time, and the display alarm can be performed, so as to master the scientific training intensity. Through the research and analysis of the characteristics of the portable heart rate monitoring system, in order to improve the real-time, reliability and anti-interference ability of the system, we require the design of the system microcontroller processing module (MCU) based on Atmega64L.

2 MCU Atmega64L

Atmega64L is a low-power 8-bit CMOS microcontroller based on the enhanced AVR RISC structure. Due to its advanced instruction set and single-clock cycle instruction execution time, the data throughput is as high as 1MIPS/MHz, there are 6 sleep modes, and the power consumption is low, making it suitable for portable product applications.

3 Atmega64L peripheral circuit design

The peripheral circuits of Atmega64L mainly include: power module, keyboard control module, LCD display and voice alarm system interface, heart rate acquisition signal input interface, see Figure 1.

The circuit design is completed in the development software ProtelDXP, including the design of the schematic diagram and PCB diagram. The selection of components and the packaging design are all based on standard regulations, but in order to meet the miniaturization requirements, some components are measured physically to load the component library by themselves, considering their surface mount type or other factors. The module circuit design adopts typical circuits.

4 Software Design

WINAVR is a development program set for AVR series microcontrollers under the Windows platform. It uses C language programming to simplify the software structure and improve programming efficiency. The system software design mainly includes: A/D conversion module, keyboard input module, threshold comparison and judgment module, display and alarm system.

(1) A/D conversion module: After the heart rate acquisition circuit uses a differential circuit and a filter circuit, it outputs an analog signal. The microcontroller Atmega64L converts the analog signal into a processable digital signal through its own ADC converter. At this time, the heart rate signal is in the form of a discrete signal, and the heart rate value is converted by calculating the time between R waves per unit time; (2) Keyboard input module: Before pre-measurement, the age parameters of the subject can be manually input for threshold comparison and judgment, mainly heart rate value; (3) Threshold comparison and judgment module: After the threshold judgment, the microcontroller sends the judgment result to the LCD display for display.

If the result of the person being measured exceeds the threshold range, the system activates the alarm system, and performs frequency-divided flashing and buzzing alarms respectively. At the same time, the measurement results are stored. In order to avoid storage redundancy, the system only retains the data of recent measurements; (4) Asynchronous serial communication module: When the system is turned on, the LCD chip will be initialized and the boot screen will appear. Then, when working normally, the heart rate measurement value will be displayed in real time. During the heart rate signal monitoring process, if the measured signal is greater than the threshold, the system will send an alarm signal and trigger the alarm function. Otherwise, it will work normally.

5 Discussion

Atmega64L is used to design a soldier heart rate monitoring system. Due to the single-chip microcomputer and its peripheral functional circuits, combined with the C language software design under the WINAVR environment, the system achieves real-time, sensitivity, and miniaturization, so that it can be carried by a single soldier. However, the system intelligent software design is not yet mature, for example: the threshold input and keyboard functions are relatively simple, and the data transmission and data storage expansion are limited.