Circuit diagram of electronic scale using tension-compression sensor

　　Electronic scales using tension-compression sensors are more accurate, cheaper, and less susceptible to damage than ordinary pressure sensors, so they have broad application prospects. This electronic scale can be used in occasions such as batching and force measurement in factory production. It has the advantages of accurate measurement, high resolution, not easy to be damaged, and cheap price.

　　The electronic scale circuit is shown in the figure. The main integrated circuit MC14433 is the A/D conversion integrated block, 4511 is the LED display driver integrated block, 1413 is the bit selection chip, 1403 provides a stable comparison voltage for the main integrated circuit, and 7650 is a chopper-stabilized monolithic integrated operational amplifier to amplify the sensor output. voltage signal. The sensor uses a BLR type tension-compression sensor. RA, RB, RC, and RD in the figure are the strain resistors in the sensor. The voltage stabilizing circuit 7805 provides 5V voltage to the entire circuit. The input voltage of 7805 works normally at 8-15V. It can also be used to step down, rectify and filter AC 220 V before providing it to the instrument.

　　Since the instrument is used in high-precision situations, the resistor-capacitor components around the 14433, 1403, and 7650 should be selected with low temperature coefficients and good thermal stability, and the resistors should be RJ metal film resistors. The difference between the two 1k resistors of the 7650 and the difference between the RE and RF resistors should be less than 1%, otherwise the scale may not be able to adjust to zero after the installation. The RE and RF resistance values ​​range from tens of k to hundreds of k, depending on the size of the selected sensor. If the sensor has a small range, such as 200kg, choose a smaller resistance value; if the sensor has a large range, such as 2000kg, choose a larger resistance value. If you want to use a decimal point to express, the decimal point resistor is connected to V+. When using a sensor with a range of less than 200kg, connect it to the decimal point before the first digit from the right. When the sensor range is between 200ks and 2000kg, the decimal point will not light up at all, and the minimum resolution is 1kg.