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Sensor inventory inside smart wearable devices

June 29, 2021

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If you know smart wear, you should be familiar with the built-in sensors, such as the optical heart rate sensor that everyone is very familiar with. It is precisely because of the popularity of optical heart rate sensors that the cost of heart rate monitoring has become lower, and we also It is seen in more and more smart wearable devices. So in addition to the common heart rate sensors, what other sensors are hidden inside smart wearable devices? And how do they function? Today we will take a closer look.


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1. Acceleration sensor



Among the sensors of the smart bracelet, the motion sensor is the most basic. It includes an acceleration sensor, a gyroscope, an electronic compass sensor, an atmospheric pressure sensor, etc. Among them, the acceleration sensor and the gyroscope should be two familiar to everyone. By measuring the direction and Acceleration force determines whether the device is moving, so as to achieve the purpose of step counting, and through the collected data to match the type of exercise the user is doing, and then monitor the user's number of walks, calorie consumption, etc., to achieve the most basic functions of the smart device.


2. Optical heart rate sensor


The optical heart rate sensor is the most commonly used heart rate monitoring device for smart bracelets. When the capacitive light shines on the skin, the light reflected back through the skin tissue is received by the photosensitive sensor and converted into an electrical signal, and then converted into a digital signal through the electrical signal. Heart rate can be measured by the light absorbance of, and with the continuous reduction of costs, optical heart rate sensors have become one of the most popular sensors in smart wearable devices.


3. Bioelectrical impedance sensor


As another sensor for monitoring heart rate, bioelectrical impedance sensors are more common in smart bracelets. For example, the JawboneUP3 bracelet used this method to monitor heart rate. The principle is also relatively easy to understand. It can monitor blood flow through the body's own impedance, and convert it into specific heart rate, respiration rate and skin electrical response index. It is a more advanced comprehensive biosensor.


However, the shortcomings of this method are also obvious. For example, the circuit is more complicated, the PCB space is relatively large, it is susceptible to electromagnetic interference, and the sensor must be close to the skin when measuring, so it is less used in smart bracelets.


4. Global Positioning System (GPS)


Everyone is familiar with the positioning of mobile phones, but the popularity of positioning systems in smart bracelets or watches is not very high. Only some professional sports bracelets or watches have GPS chips, and due to the high cost, such The price of the product will also be higher. For example, Garmin fenix5X, which has built-in GPS, GLONASS, Beidou satellite positioning system, it can be used to record the user's geographic location, running route, realize trajectory planning, and track return. It is absolutely necessary for people who like outdoor sports. .


5. Electric skin response sensor


The galvanic skin response sensor is a more advanced biosensor used to measure human arousal, and a large number of scientific research experiments have proved that the arousal is closely related to human attention and participation. It is usually equipped in some On equipment that monitors sweat levels. From a professional point of view, the skin resistance and conductance of the human body change with changes in the function of the skin's sweat glands. These measurable changes in skin electrical activity are called electrical skin activity (EDA). Psychophysiologists measure the sweat gland activity caused by psychology to study the psychological activity related to it. This is also an important basis for some bracelets to provide users' mood index.


6. Temperature sensor


As the name implies, the temperature sensor is mainly used to detect the temperature of the user's skin. It measures the surface temperature of the skin through direct contact with the user's skin. However, due to the way the watch is worn, the body surface temperature cannot replace the body temperature, but can only be used as A kind of indirect reference data, and relatively few applications in smart bracelets.


7. Air pressure sensor


Everyone should be familiar with the air pressure sensor. It can measure the air pressure at the user's location to calculate the altitude. It is commonly used in sports watches or bracelets. It can calculate the location of the location through the weak air pressure changes during exercise. Altitude changes, while the accuracy can be controlled within 10CM during the height movement of a 10-story building. Data from climbing to climbing stairs can be monitored. It is also one of the indispensable sensors in professional sports watches.


8. Capacitive sensor


This may be rarely mentioned, but the application is actually very wide. For example, many bracelets have a wrist-off detection function. In fact, the capacitance sensor is used to monitor the change of the capacitance voltage, and the algorithm automatically detects whether the user is wearing the hand or not. Ring, remind users in time, and even play a role in preventing loss. In addition, the capacitive sensor can actually avoid misjudgment of sleep and heart rate monitoring in scenarios where the bracelet is not worn.


9. Hall sensor


The Hall sensor is a magnetic field sensor made according to the Hall effect. It is used in bracelets or earphones. It mainly uses the built-in magnet on the wristband of the wristband to sense the change of the magnetic flux between the earphone or the wristband to determine whether the earphone or watch/band is in the state of being worn. At the same time, it can also control the playback/pause of the earphone to achieve "just take it off" "Stop, put on and listen" function.


10. Ambient light sensor


In smart wearable products, the battery life of the smart watch has always been a pain point, and in order to further extend the battery life, the ambient light sensor has almost become one of the standard configurations of the smart watch. In terms of principle, the ambient light sensor can sense the surrounding light and inform the processing chip to automatically adjust the brightness of the display's backlight to reduce the power consumption of the product. At the same time, the ambient light sensor is also widely used in mobile devices such as mobile phones, notebooks, and tablets.