Unlike traditional pedometers, the belt-type pedometer is embedded inside the belt, which reduces the size of the wearable device and eliminates the “second-wearing†problem of the wearable device, and relies on the high-precision, low-power ADLX345 sensor. Accurate step counting, the experiment shows that the belt type pedometer has small volume, simple structure and high stability, which can meet the step counting requirements.
With the advent of the Internet era, more and more intelligent devices help people to live quality. The pedometer is a wearable tracking device that can record walking steps and improve sports fun. Unlike traditional pedometers, the belt-type pedometer is embedded inside the belt, which reduces the size of the wearable device and eliminates the “second-wearing†problem of the wearable device, and relies on the high-precision, low-power ADLX345 sensor. Accurate step counting, the experiment shows that the belt type pedometer has small volume, simple structure and high stability, which can meet the step counting requirements.
In today's society, with the development of the economy, people's living standards are getting higher and higher, and the pace of life is getting faster and faster. Accompanied by the general decline in people's physical fitness, problems such as excessive weight and sub-health are widespread. People are also paying more and more attention to their physical health problems, and exercising is the most effective way to keep themselves healthy. As a wearable health tracking device, the pedometer can record the number of walking steps of the person, and feedback the accurate exercise data to the wearer, help the wearer to quantify the exercise intensity, formulate a reasonable fitness plan, remind the wearer to adjust the exercise amount appropriately, and motivate the wearer. The person insists on exercising.
Currently pedometers are available in both mechanical and electronic versions. The mechanical pedometer relies on the vibration of the internal reed to generate electronic pulses, which in turn achieves the function of step counting. Its accuracy and sensitivity are low. The electronic pedometer achieves the function of step counting by measuring the change in acceleration when the human body walks. Electronic pedometers have better accuracy and sensitivity. Some electronic pedometers require certain wearing parts, such as the waist, wrist, etc.; some do not require the wearing part, as long as they are placed in the pockets around them, the handbag can be counted. In general, the pedometer wearing the wrist and the pedometer that does not require the wearing part are more difficult to implement accurate step counting, and the development cost is also high. The pedometer worn at the waist makes it easier to implement accurate step counting functions at a lower cost. They all need to be "secondary wear".
1 hardware design1.1 ADXL345 sensor
The pedometer consists of ADXL345 accelerometer, STC90C51 MCU, LCD1602 display, zero button, and other parts. Powered by the battery. The ADXL345 is a small, thin, ultra-low power 3-axis accelerometer with a measurement range of ±16g. Its high resolution (3.9mg/LSB) enables measurement of tilt angle changes of less than 1.0°. The basic workflow is: firstly, the three-axis sensitive unit is sensitive to three directions of acceleration, and then the physical quantity is sensed by the electronic sensing device, and then converted into a digital signal by A/D sampling, and then digitally filtered and sent to control and interrupt. Logic, interacting with the master device through the serial I/O port under the control of the command word.
1.2 IIC bus communication
The ADXL345 has two ways to communicate with a microprocessor (microcontroller): SPI and IIC. The communication method we use is the IIC bus communication method. The IIC bus consists of the data line SDA and the clock line SCL, which can send and receive data. Bidirectional transfer between the CPU and the controlled IC, IC and IC, the maximum transfer rate is 100Kbps. The main advantages of the IIC bus are: 1. The occupied space is very small, which reduces the space of the board and the number of chip pins, and reduces the interconnection cost. 2. Support multi-master, any device that can send and receive can become the master device. The IIC interface mode is enabled if the CS chip select pin is tied to VDD I/O high. IIC A variable address 0x53, may be selected by pin SDO, the write operation is 0xA6, and the read operation is 0xA7. The work is as follows: first start the IIC bus, prepare for data transmission, then send the storage unit address to the slave device (ADXL345), and then continuously read the six address data and store it in the acceptance data buffer area. After receiving the slave device ( ADXL345) sends an acknowledge signal to the master device (microprocessor), and finally sends a stop signal, indicating that the transmission of one data is terminated and the IIC bus is idle.
1.3 STC90C51 single chip microcomputer
The STC90C51 microcontroller is a new generation of ultra-anti-jamming, high-speed, low-power, enhanced 8051 microcontroller from Hongjing Technology. It integrates a central processing unit (CPU), program memory (Flash) and data memory on a single silicon chip. (SRAM), timer/counter, UART serial port, I/O interface, EEPROM, watchdog and other modules. Has a computer property. The STC90C51 operates from a 3.3V to 5.5V supply with 40 pins and 35 general purpose I/O ports.
The STC90C51 is connected to the ADXL345 at one end to process and judge the data transmitted by the ADXL345, and the other end is connected to the LCD1602 display to transmit the command display and displayed data to the LCD1602. At the same time, there are zero return buttons, power off buttons, and so on.
1.4 LCD1602 display
The LCD1602 character LCD screen used in this design is used as the display interface of the system. The LCD1602 display is a dot matrix liquid crystal module designed to display letters, numbers, and symbols. It consists of a number of 5 ╳ 7 or 5 ╳ 11 dot matrix characters, each of which can display one character. Among them, pin number 1, 2 is the power supply terminal; pin number 3 is the liquid crystal display bias signal, used to adjust the display contrast; number 4 is the data / command selection end, connected to the microcontroller P1.0 port; number 5 is read / Write select terminal, connected to the P1.1 port of the MCU; No. 6 is the enable terminal, connected to the P2.5 port of the MCU; No. 7 to No. 14 are 8 data I/O ports; Pin No. 15 and 16 are the backlight Source power terminal. First, initialize the LCD1602, set the cursor, pointer and other data, then write the command, set the display position of the symbol, and finally, write the characters to the display continuously, and the LCD1602 display will display the characters.
2 human walking modelPeople have many parameters that change during walking, such as distance, energy, and acceleration. It is a simple and feasible method to describe the walking characteristics of people through acceleration changes. It is most accurate to detect the number of steps from the acceleration of the foot, but considering the convenience of carrying, we choose to use the motion of the waist to detect the number of steps. The acceleration of the movement of the waist can be decomposed into a vertical axis, and the advancing axis has three directions of the lateral axis. As shown in Figure 1. The ADXL345 is a three-axis (X-axis, Y-axis, and Z-axis) analog output accelerometer that acts as a sensor for vertical, lateral, and forward directions. as shown in picture 2. It can be seen from the figure that there are more obvious periodic characteristics in the direction of the vertical axis (X axis) and the forward axis (Z axis). The minimum value of the vertical axis acceleration corresponds to the foot leaving the ground (the beginning or end of the step), and the maximum value corresponds to the foot being raised to the highest point. The minimum acceleration of the forward axis corresponds to the foot leaving the ground (start or end of the step), and the maximum value corresponds to the foot being raised to the highest point.
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