Smart bracelet, as a popular product form in the past two years, has attracted more and more attention from people. Although it cannot be accepted by all people, its emergence has indeed brought about some changes in the market of electronic products.
A smart bracelet is usually composed of radio frequency circuit unit, clock circuit unit, memory circuit unit, sensor circuit unit and main control MCU unit, etc., and the circuit PCB is usually concentrated in a small range, single or double sided chip, circuit board is mainly 4 or 6 layers. The following picture shows the circuit PCB of the smart bracelet.
Since so many functions are concentrated in a small PCB board, so we should pay special attention to the layout and wiring of the bracelet, now summarize some points for attention, for reference.
1. PCB circuit partition layout, pay attention to line protection
As can be seen from the above PCB circuit board, the circuit of each part of the smart bracelet (marked by boxes in different colors) has a good partition: since the smart bracelet is a collection of digital circuit components, as long as the matching resistance and capacitance distribution is done in the circuit design, the circuit module with certain functions can be completed, which makes the circuit design more concise and easy to find. Although some sensor circuit units use analog circuit technology for data acquisition, once the module is designed as a module, then data communication and information transmission can be completed through the corresponding connection interface.
In the layout of circuit modules, on the one hand, it is necessary to pay attention to the clock circuit and crystal oscillator circuit to reach the target through the shortest path. On the other hand, it is necessary to avoid the data line when the clock is running, so as to prevent interference affecting the stability of the system.
During cabling, it is necessary to protect key cabling, such as whether to apply copper protection to clock generating circuit, crystal oscillator circuit, etc., or whether to carry out ring ground protection, etc. Generally, protection will be carried out in the design. For the crystal oscillator part, copper mining is required.
Two, PCB design to deal with the RF circuit
The smart bracelet needs to be connected with the mobile phone when it is used. Therefore, the radio frequency part is the key part. In this part of design, we must pay special attention to it. Now the smart bracelets on the market are nothing more than wireless data transmission based on Bluetooth, so the focus is on Bluetooth RF processing. If the smart bracelet is only used for data transmission without the transmission of sound and music, then low-power Bluetooth is the best choice. In the design process, the shape of Bluetooth antenna, antenna layout and the shell material of smart bracelet are all important factors affecting the performance of smart bracelet. In the PCB design process of smart bracelet, an excellent RF antenna engineer is particularly important.
3. Do a good job in ESD protection design
In the previous article, I also talked about some technology and knowledge of circuit ESD. Today, I will talk about the importance of ESD to smart bracelet products. Different countries and regions have different standards for ESD requirements of different products or the same product. In order to make the product pass the relevant detection, ESD protection design should be carried out during the design, and ESD detection should be carried out after the design is completed to ensure that the product can adapt to the electronic detection of the local market.
Iv. Reserve system upgrade interface
The convenience of upgrading the functions of a smart band is of great significance to the users, or the avid fans of the smart band. If the software of a product is upgraded at an appropriate time (it may be because the software fails to catch up with some functions in the early hardware design, or some bugs in the software are fixed), it indicates that the product is still in the process of continuous research and development, which is a good psychological compensation for users. At present, there are usually two ways to upgrade the software of smart bracelet: via USB interface and wireless push method. As for which method to adopt, it needs to be determined in the preliminary planning and software and hardware planning.