PCBA scheme development -- portable electronic scale scheme

The portable electronic scale has the advantages of high weighing accuracy, simple and practical, convenient carrying, low cost, simple manufacture, accurate measurement, high resolution, not easy to damage and low price. It is the first choice for family shopping. The circuit consists of measurement circuit, differential amplification circuit, a / D conversion and display circuit. The most important component in the measuring circuit is the resistance strain sensor. Resistance strain sensor is one of the most widely used sensors. It is widely used in electronic scales and measuring devices with various new structures. The function of the differential amplifier circuit is to amplify the weak analog signal output by the sensor to a certain multiple, so as to meet the requirements of the A / D converter for the input signal level. The function of a / D conversion is to convert analog signal into digital signal, carry out analog-to-digital conversion, and then transmit the digital signal to the display circuit. Finally, the display circuit displays the measurement results.

Performance parameters of electronic scale scheme:

Startup mode: automatic weighing and startup, with a weight of 5.0kg + 0.1kg.

Unit and display division: two units kg and IB are supported, and the corresponding division values are 0.1kg and 0.2lb,

Toggle the switch to change the unit.

Weighing range: 3.0kg ~ 183.0kg

Voltage and current: during normal operation, the power supply voltage of the sensor part is 2.3V, the working current is 6mA, the standby current is 1uA, and the scanning current is 200uA.

Calibration: three point calibration, 50kg, 100kg and 150kg respectively.

Low power prompt: when the battery voltage is lower than 2.4 + 0.1V, the LCD displays "Lo", and it will stand by automatically after 4 seconds.

Overload prompt: when the weighing value is greater than 183.0kg, the LCD will display "ol".

Automatic standby time:

After locking the weight: 10 + 1s;

Unstable shutdown: 20 + 1s;

After startup and zeroing: 10 + 1s;

Return to zero: return to zero after the power on full display is stable; in the weighing state, the weight is less than 3kg and automatically returns to zero after it is stable;

Temperature and humidity characteristics: the working temperature of the chip is - 40 ° C ~ 85 ° C, and the relative humidity: ≤ 90%.

Working voltage: 2.4V ~ 3.6V power supply

Memory range: three groups of memory values, the memory range is 0.3 + - 0.1kg

Backlight: the backlight is on when starting up or weighing, and the backlight is off after 10s when weighing is stable or no operation

Functional features of electronic scale scheme

Working voltage: 2.4V ~ 3.6V

Support LCD / L.Ed display

Weighing range up to 183kg

With 3 groups of memory values

Normal weighing function

Two units kg and LB are supported

Low power prompt