Design of automatic discriminating circuit for low power BJT pin tube type

In electronic technology, the triode is a very common component. The parameters of the three-stage tube are closely related to the measurement scheme and measurement results of many electrical parameters. Therefore, in the electronic design, the pins of the triode, The type of judgment and measurement is very important. There are many methods for measuring the triode pins. The commonly used ones in the laboratory are to measure the characteristics of the pins of the multimeter and the triode. However, due to the complicated relationship between the voltage and current between the pins of the triode, and the small size of the triode itself, The measurement brings great inconvenience, and there is currently no device for automatically determining the type and type of the triode tube. Therefore, it is especially important to design a circuit that automatically discriminates the triode pins and types.

1 hardware circuit composition principle

According to the types of commonly used triodes and the arrangement of the pins, the automatic discriminating circuit designed includes four parts: the central control unit, the conversion circuit, the detection amplifying circuit and the display circuit, as shown in Fig. 1, in which AT89C2051 is used as the central control unit.

Figure 1 System block diagram of the discriminator

2 hardware circuit design

Figure 2 shows the schematic diagram of the automatic identification hardware circuit of the triode pin type. The hardware circuit mainly includes the single chip AT89C2051, the inverter CD4069, the photocoupler 4N25, 74LS06, 74LS07, several resistors and capacitors.

Figure 2 Discriminating circuit schematic

Figure 2 Discriminating circuit schematic

First, three binary codes (high and low levels) are sent from the P3.0~P3.2 ports of the MCU, and sent to pins 1, 2 and 3 of the triode. For different triodes, when the MCU sends different codes, the current directions on pins 1, 2, and 3 are different, there are two cases of inflow and outflow, and two optocouplers are used in reverse parallel to detect which direction. A current passes through, and the three-digit binary code becomes a six-digit binary code. The detected electrical signal from the optocoupler is amplified. Since the output signal is not the standard high and low level, it cannot be directly recognized by the single chip microcomputer, and the phase does not meet the requirements. Therefore, the first stage inverter CD4069 is used for inversion. Then, the standard six-digit binary code output from the inverter is sent to the P1.0~P1.5 ports of the microcontroller. The MCU compares the data read from the P1 port with the data written in advance by the MCU. When the corresponding conditions are met, the detection result is output from the P3.3~P3.7 port, and finally the LED is used to display the corresponding triode type.

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