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Working Principles of the Smart Watch

Jan 17,2022

Some of the features a smart watch might have are extensions of what a smartphone can do. For example, by designing it to alert a phone call or a tweet, users no longer need to take their phone out of a pocket, backpack or handbag, and smartwatches have unique advantages in sports and fitness. In addition, safety smart watches also have great advantages in mobile payment and other aspects. The following is a detailed introduction to the working principle of the three major functions of smart watch detection of steps, heart rate monitoring, and positioning.

1. Principles of the safety smart watch to detect the number of steps

(1) Sensor detection

smart fitness bracelet watch sensor can sense motion conditions such as acceleration or vibration in different directions through a capacitive accelerometer. The three-dimensional rhythm motion state sensor is divided into three-axis and six-axis. The three-axis generally records data by swinging the arm, while the six-axis will record data and improve the movement and precision through walking, running, cycling, and climbing stairs.

(2) Software algorithm

According to the three-dimensional data captured in real time by the three-axis acceleration, through filtering, peak and valley detection and other processes, using various algorithms and scientific and meticulous logical operations, these data are finally converted into readable numbers on the watch APP side, step by step, the number, distance, and calories burned are displayed.

(3) Green light photoelectric measurement method

It consists of two green wavelength light-emitting LEDs and a light-sensitive sensor located on the back of the watch. The principle is based on the change in the light transmittance caused by the density change of the blood in the blood vessels of the arm when it flows. The light-emitting LED emits light waves of green wavelengths, and the photosensitive sensor can receive the reflected light from the skin of the arm and sense the change in the intensity of the light field and convert it into heart rate. The smart fitness bracelet watch can continuously measure the heart rate, calculate the average heart rate, and record the maximum heart rate.

2. Principles of the safety smart watch monitoring heart rate

Generally speaking, the principles of heart rate monitoring are usually divided into three types: one is the photoelectric transmission measurement method. In principle, the sensor in contact with the skin of the watch will emit a beam of light on the skin to measure the reflected and transmitted light. Because blood absorbs light of a specific wavelength, every time the heart pumps blood, that wavelength is absorbed in large quantities, and the heartbeat is determined. Most of the heart health smart watches on the market use the photoelectric transmission measurement method. Another method is to test the ECG signal. The sensor of the watch can judge the user's heart rate by measuring the electrical signal of myocardial contraction. The principle is similar to that of the ECG. The disadvantage is that the circuit is relatively complex, occupies a large PCB space, and is susceptible to electromagnetic interference. At the same time, the sensor must be close to the skin and the placement position is relatively fixed, so it is difficult for smart watches to use this measurement method.

3. Principles of the safety smart watch positioning

(1) GPS Global Positioning System

The basic principle of GPS navigation system (United States) is to measure the distance between a satellite with a known position and the receiver of the user, and then combine the data of multiple satellites to know the specific position of the receiver. It is composed of space part + control part + user part, the precision is more than 3 meters. This system is not something that ordinary countries can build. It depends on its economic strength and technical level. There are three mature and one under construction satellite positioning systems in the world. The existing satellite navigation and positioning systems include the US Global Satellite Positioning System ( GPS) and Russia's Global Positioning System, as well as China's Big Dipper, Europe's Galileo.

(2) LBS base station positioning

The principle of base station positioning: the mobile phone measures the downlink pilot signals of different base stations, and obtains the TOA or TDOA of the downlink pilot frequencies of different base stations, the accuracy is not high, more than 100 meters.

(3) WIFI hotspot

WiFi can locate users. Since each WiFi hotspot has a unique Mac address, bluetooth fitness tracker watch will automatically scan the nearby hotspots and upload their location information after the WiFi is turned on, with an accuracy of less than 10 meters.

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