According to the data of AT89C51 and HX711, the circuit principle of the weighing instrument is shown

The digital display weighing instrument designed in the article is a weighing control display device based on a resistor strain force sensor and a single-chip microcomputer design. The detection range is 0-10kg, the measurement accuracy is ±2g, and the LCD display shows accurate information. Measurement data information, in addition, several accurate measurement data information can be sent to the electronic computer to display information according to the serial port. The system software has the characteristics of high precision, stable characteristics, and simple actual operation. The frame diagram of the weighing instrument design scheme is shown in Figure 1 below: 1. Hardware configuration circuit principle 1.1. Load cell resistor strain force type load cell consists of resistance strain gauges, polyurethane elastomers and inspection power supply circuits. Part of the composition. The polyurethane elastomer causes elastic deformation under external force, and the resistance strain gage attached to its surface also causes deformation. After the resistance strain gage is deformed, its resistance value will change (expand or decrease), and then be relatively accurately measured The power circuit transforms this resistor into an electronic signal (working voltage or current), and then completes the whole process of converting the external force into an electronic signal. Check the power supply circuit as shown in Figure 2, and change the resistor of the resistance strain gauge into a working voltage output. Because the Wheatstone bridge has many advantages, such as the ability to suppress the hazards of temperature transitions, the ability to suppress the influence of lateral forces, and the ability to more easily deal with the compensation problem of the weighing sensor, the Wheatstone bridge has gained the advantage of the weighing sensor. Universal use. The load cell generally has a total of four output wires. The output resistance is generally 350Ω, 480Ω, 700Ω, 1000Ω. The input terminal will generally carry out some temperature and sensitivity compensation. The input terminal resistor will be 20-100Ω higher than the output terminal. The output terminal can be distinguished by measuring the resistance value with a digital multimeter. 1.2. The output data signal of the strain force type load cell of the amplifier circuit is not strong (mV or even μV heavyweight), and there is often a lot of noise along with it. For such data signals, the first step in the power supply circuit is generally to select an instrumentation amplifier to first increase the small data signal. The instrumentation amplifier power circuit has a stronger common-mode rejection capability than a simple differential signal amplifying circuit. The most important purpose of increasing is not the gain value, but only to improve the frequency stability of the power supply circuit. In this design, the instrumentation amplifier uses the OP07 three operational amplifier structure. As shown in Figure 3 diagram. When R1u003dR2, R3u003dR4, Rfu003dR5, the gain value of the power supply circuit is: Gu003d(1+2R1/RG1)(Rf/R3). It can be seen from the formula calculation that the adjustment of the gain value of the power supply circuit can be completed by changing the resistance value of RG1. 1.3. A/D conversion power supply circuit The A/D converter selects the electronic scale dedicated integrated icHX711, which is a 24-bit A/D converter integrated ic designed for high-precision electronic scales. Compared with other integrated ICs of the same type, this integrated IC integrates the peripheral circuits necessary for other integrated ICs of the same type, such as an adjustable regulated power supply, an on-chip clock and watch oscillator. Enter the switch to select safe channel A or safe channel B at will, and the internal low-noise program controller amplifier between the two is connected. The gain value of the program controller of the safety channel A is 128 or 64, and the corresponding full credit differential signal input data signal amplitude value is each ±20m