Understand the importance of chip crystal oscillator by disassembling outdoor sports smart watches

With the development of intelligent technology, watches are no longer just looking at time, but more roles are added to let watches. However, the key to realizing these functions lies in crystals. Next, we will decompose an outdoor sports smart watch to understand the application of chip crystal oscillator in intelligent consumer electronics. What will be removed is the 47 mm diameter FeNi 5 + sapphire version, which includes sapphire glass lenses according to its name (dome and chemically strengthened glass options are also available). This special model also provides stainless steel titanium ring selection. Other main features include: semi inverse translucent pixel memory with a diameter of 1.2 inches (30.4 mm), 240x240 pixels, power optimized (MIP) display (Note: touch screen is not supported); Wi Fi, Bluetooth, low power Bluetooth (ble) and ant + connection options; Support near field (NFC) for Garmin payment and contactless payment function; Support global positioning system, global navigation satellite system and Galileo global satellite positioning service; Wrist heart rate monitor (my Pioneer watch uses a chest strap and is connected to the watch through ants); A series of built-in technologies: barometric altimeter, compass, gyroscope, accelerometer and thermometer; Built in speakers (various). Instead of the increasingly popular OLED, which relies on the reflected light illumination of the surrounding environment, it only provides a transmission backlight supplement when necessary (for example, the user presses a button to activate), so it has a "half back half light" name . it also contains embedded pixels based on SRAM memory, so there is no need to constantly refresh the display DRAM. These two functions are obviously designed to minimize power consumption. That's it: there is no touch screen (considering that the fingers may be wet and cold when the watch is used outdoors) , if the touch screen does not work normally due to cold, dirty or gloves, and there is no local voice control, it is undeniable that it competes with apple watch, Fitbit and Google wear operating system. In contrast, this user interface feels a little "old-fashioned", but considering its target market, this problem is not important.
There is an optical capacitance product pulse wave optical heart rate sensor in the middle and a special four piece connector on one side to realize charging power and data transmission. The PCB drive display is realized by connecting the PCB with wide copper wire and narrow black wire, which is connected to the NFC antenna. The copper disk above the Faraday protective cover is a simple speaker, which extends from the printed circuit board (PCB) and three are on the side (spring support) The metal rod provides the connection with the front ring, which is also used as a GPS antenna. The positioning function depends on the packaging of 3225 crystal oscillator and 2520 crystal oscillator to reduce space and achieve high-precision stability.
Note that the four conductive pads of the back connector are connected to the PCB itself through the back, indicating that they can be used for data transmission or to manage the charging process on the PCB. It uses 225mah lithium ion. Next is the tactile motor, and below is the optical heart rate sensor. I dare not try to remove the battery and expose the sensor. It is based on the main system CPU, Freescale (now NXP) mk28fn2m0acau15 kinetics K28 however, the Faraday cage corner has a large integrated circuit, and its identity is a mystery. Another Jiaming watch (model: a03405) has a watch similar to IC, and FCC has a photo claiming to be a Wi Fi transceiver, but because we are already there
The other side of the PCB recognizes the chip, so we know that this is not the case in this special design. Given its proximity to the processor, I suspect it is an unknown manufacturer and capacity SPI flash memory storage system. There is a firmware revision label on code 1. Kinetic K28 contains enough 2 Mb embedded flash memory to boot the system, but it does contain the NAND flash module mentioned earlier To save the code and load it into DRAM for execution, but I guess it will
It is only used to store nonvolatile data. We can see that the time required to connect the key SMD crystal oscillator to Bluetooth data transmission is 32.768k crystal oscillator. There are three crystal oscillators on the board. In addition, there are GPS crystal oscillator, Bluetooth crystal oscillator, WiFi crystal oscillator and voice. Small volume frequencies such as 26m, 32m, 16m and 27m can be selected. There are many kinds of electronic components used in the circuit board, Including sensors, capacitors, integrated circuits, chips, gyroscopes, accelerators, etc. since Bluetooth, ble, Wi Fi and ant + all share the same ISM frequency band, I suspect that this is for the sake of cost saving and simplicity, because they also share the same antenna. I guess it is embedded on the printed circuit board rather than a separate antenna.

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