PCBA design of body fat scale

　　 The pace of human life is fast 、 Irregular diet and other current situations have caused many people to gain weight , Obesity is known to cause “ Three tenors ” problem , To lose weight 、 Weight loss has become a major health topic of great concern . People who want to do good things must first sharpen their tools , If you want to lose weight, you should also have a good partner , Bluetooth smart body fat scale, which can measure body weight and body fat at the same time, has gradually become the mainstream .

　　 Its most basic function is Bluetooth smart body fat scale ：

　　1、 Weight measurement ： stand up 1~3 Seconds later , The scale can accurately display the weight ;

　　2、 Measure the body fat rate ： Stand barefoot on the scale , You can analyze the body fat ratio through your feet , The scale will automatically store the recorded information , Fast analysis BMI( Body mass index );

　　3、 Connect your phone wirelessly APP： Synchronize weight and body mass index to APP/ Cloud database, etc ; Besides , You can also turn on the alarm function , The scale will automatically remind you to weigh , After completing the weight , The alarm clock will stop automatically .

　　 One 、 Weight measurement .

　　 Weight measurement , It is mainly based on the principle of strain electrometry . Attach a strain gauge to the elastomer of the load cell , Constitute Wheatstone bridge . When there is no load , The bridge is in balance , The output is zero . When the elastomer is under load , Each strain gauge then produces a strain proportional to the load , And release a certain strain voltage in the chip , Then the amplified voltage signal is changed into a digital signal by the analog-to-digital conversion module , Finally, it is sent to the microcontroller for processing 、 Show , So as to achieve weight measurement .

　　 Principle analysis of load cell ：

　　 The principle of the pressure gauge is to stick the strain gauge to the aluminum bar , Strain gauge composed of bridge resistor , When the aluminum bar is stressed , Will cause deformation , So that 4 A resistance produces a strain coefficient .

　　 One 、 Brief introduction of intelligent fat scale scheme

　　1、 Startup mode ： Power on by gravity or power on

　　2、 Display accuracy ：1500 Graduation ;

　　3、 Company ：KG、LB、oz;

　　4、 Calibration method ：3 Point calibration , The calibration position is 50Kg、100Kg、150Kg;

　　5、 Memory function ： Memory range ：0.3±0.1Kg; Remember time ： Long term memory ;

　　6、 Low voltage detection ： Power on to detect low voltage , A little detection ;

　　7、 Shut down time ： After the weight is stable ,8±2 Second automatic shutdown ;

　　8、 Power waste ： stay 2K In the case of sensors , The operating current is less than 2.5mA; The average shutdown current is less than 15uA;

　　9、 Low voltage indication ： Show “Lo”4s Power off after ;

　　10、 Backlight control output ： nothing

　　11、24LC02 Storage ： Yes

　　12、 Communication mode ： bluetooth 、WiFi

　　 Two 、 Basic functions of intelligent fat scale scheme

　　1、 Weight parameters

　　1) Weighing unit ：Kg

　　2) Heavy weighing ：152.0 Kg

　　3) Lifting weight （ Small display weighing , Zero tracking range ）：5.0 Kg±0.1 Kg

　　4) Zero range ：6.0 Kg

　　2、 system function

　　1)E2PROM(24LC02) To detect ： Check whether there is 2402, If there is no such parameter, it will display E2PROM Error screen “ErrE”;

　　2) Calibration test ： Check whether it enters the correction mode , Usually used before leaving the factory ;

　　3) Power on low voltage detection ： When the voltage is low 2.4V±0.2 V Low voltage symbol is displayed ;

　　4) Display weight limit ： Display the weight limit = To a great extent +10g, If it is overloaded, the overload screen will be displayed “O-Ld”;

　　6) When there is no key operation and the weight does not change for a certain time , Will automatically enter sleep mode .

　　3、 Key operation

　　1） The power button , Short press to start , Long press to turn off .

　　2） The power button , After power on , Short press the unit to switch .

　　3） The power button , After power on , Wait until the display is fully displayed , Press the power on button quickly “ Three short and one long ” Enter calibration mode , Place weights as shown , After the operation is completed, it displays “pass”