The circuit schematic of the analyzer is shown in the figure above. The whole circuit is divided into two parts: the transistors VT1 and VT2 form the detection circuit; the VT3 and VT4 form the alarm generator. The detection part is composed of a Schmitt trigger. When the needle electrodes A and B are inserted into the food, the resistance Rx of the food itself is connected to the circuit. Since the internal resistance of the food is related to the freshness of the food, the more fresh the food resistance, the greater the resistance. When the distance between the electrodes A and B is 1 cm and the insertion depth is 2 cm, the resistance of the fresh fish is 20K, and the resistance is less than 10K. When R0=5.6K in the circuit, Rx≤10K, VT1 is turned on, its collector voltage drops, VT2 cuts off, the collector voltage rises, and the sounder composed of VT3 and VR4 sounds. Due to the use of Schmitt triggers, the circuit sensitivity is high, and the circuit will sound an alarm when Rx is below a certain resistance. A mobile phone protective cover is a jacket designed and produced to protect the mobile phone. In the mid-to-late 1990s, mobile phone protective sleeves took advantage of the opportunity of slimming mobile phones to become popular, and their functions also protected the mobile phones for aesthetic purposes. phone case, cell phone case, phone cover Reteck Electronic Co., Ltd. , https://www.reteck.com
The speaker is made of 8 ohm small speaker; the needle electrode can be made of stainless steel wire or electric furnace wire, the length is 2.5cm, it is directly soldered on the circuit board, and can not be replaced by metal such as copper and zinc. Since the resistance of different foods is different, the resistance of R0 should be changed when measuring different foods. When R0=5.6K, it can be used to determine the quality of fresh fish; when R0=120K, Rx≤200K, the horn sounds, which can be used to determine the quality of pork; other foods can be determined according to the test. If a variable resistor is used instead of R0, it is more convenient to indicate different food words on the dial.
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