Design of Intelligent Circuit Characteristic Tester for Use in Harsh Environments

This paper designs and makes an intelligent circuit characteristic tester. It is used to measure the characteristics of a specific amplifier circuit, and then to intelligently determine the reasons for the failure or change of the amplifier due to the change of components.The intelligent circuit characteristic tester is driven by a single chip microcomputer (MSP32F103V) to produce a 1 kHz sinusoidal excitation signal. The influence of the output module resistance is eliminated by an impedance matching circuit, and the input is measured. The input resistance, output resistance and magnification of the measured circuit are calculated by designing the peripheral resistance at both ends of the tested circuit. The output signal of the measured circuit is filtered for DC noise and then input to the single chip microcomputer by the AD637 DC conversion module. The amplifier’s input and output resistance, magnification and fault analysis results are automatically processed and measured by the E76 module.For the result of circuit test, the tester can automatically and accurately judge and display the reason of circuit change within 2 seconds.

INDEX TERMS Integrated circuits, automatic testing, microcomputers.

I. DESIGN BACKGROUND
Electronic products are based on electronic components and circuits, which are very rich in variety and widely used in daily production and life [1]. They provide convenience to people's lives, but their failures can have serious impacts. If the electronic circuit fails, it will greatly affect the performance and security of electronic products, and even threaten the safety of people's lives and property. In electronic products, the main source of fault comes from the circuit system [2]; if the failure cannot be rectified immediately, it can cause equipment operation to fail, resulting in a greater loss [3]. Therefore, technicians should take effective measures to deal with circuit system failures, such as strengthening detection [4], fault identification and troubleshooting methods to ensure their safe operation and reduce losses [5].
In this study, we design and fabricate an intelligent circuit characteristics tester [6], measure the characteristics of a The associate editor coordinating the review of this manuscript and approving it for publication was Qilian Liang . particular amplifier [7], and then determine the components responsible for amplifier failure or change [8]. Figure 1 shows the measured amplifier circuit. The circuit diagram shows the arrangement of the components on the circuit board. Modular components with pins help ensure that each component can be easily replaced. The absolute value of the resistance relative error used in the circuit does not exceed 5%, and the absolute value of the capacitance relative error does not exceed 20%. The transistor model is 9013, and its beta value is between 60 and 300. The output port of the circuit characteristic tester is connected to the amplifier's input end (Ui), and the input port of the circuit characteristic tester is connected to the amplifier's output end (Uo).

II. DESIGN SCHEME A. BLOCK DIAGRAM OF THE OVERALL SYSTEM ARCHITECTURE
The system is composed of a signal source, impedance matching module, measured network, voltage follower and AD637 DC conversion module, and the network to be tested is a transistor amplifier. The scheme generates the sinusoidal signal with adjustable frequency through the single chip STM32F103V drive chip AD9854, eliminates the influence of the signal source output resistance through the impedance matching module, and inputs the signal to the circuit under test. It can obtain the input and output resistances and the magnification of the circuit under test. After the output signal of the measured network is processed by the capacitance voltage follower, it is converted into a DC signal for input to the single chip microcomputer (STM32F103V) by the AD637 DC conversion module. The input resistance, output resistance, circuit magnification and corresponding fault analysis are automatically measured by the debugged E76 module and displayed on the LCD display screen.

B. INTERPRETATION OF HARDWARE CIRCUIT MAIN MODULE DESIGN--SYSTEM 1) FORWARD SIGNAL SOURCE
According to the theoretical analysis, the circuit is designed as follows: AD9854 chip: Driven by a single chip microcomputer (STM32F103V), the DDS chip (AD9854) produces a stable, frequency-programmable modulated sinusoidal and cosine output when an accurate reference frequency is entered.

2) DC CONVERSION MODULE
The AC voltage is diverted to the single input end of the unipolar current-driven squared divider circuit [9]. The squared divider's output current-driven components and external average capacitance form a low pass filter, which returns the squared or divider after the output current, completes the calculation of the effective value and outputs the converted DC signal [10].

III. CIRCUIT A. HARDWARE CIRCUIT --PHYSICAL CONNECTION DIAGRAM
We connect the stm32, Arduino, camera, temperature and humidity sensor, Bluetooth module, infrared emission module, infrared receiving module, player, light intensity sensor and so on of the raspberry pi, integrated nb-iot module, as shown in Figure 4. The integrated system is then centralized inlaid into the ''doll'' and equipped with a detection function, as shown in Figure 5.

B. PROGRAMMING
The input resistance, output resistance, and gain detection module output the 1 kHz sinusoidal signal input to the circuit under test.
The output step of the amplitude-frequency characteristic detection module is a 1 kHz ∼ 200 kHz sweep frequency sine wave signal, which is input to the circuit under test.
The circuit state is obtained by comparing the data items for the 100 Hz, 1 kHz and 1 MHz input states.

C. THEORETICAL ANALYSIS AND CALCULATION OF SYSTEMS 1) SYSTEM PRINCIPLE
Let the resulting sinusoidal signal be, and the amplified signal be V I = A cos ωtV o = AK cos(ωt + ϕ). K represents the magnification and ϕ represents the magnified phase. After amplification through the effective value detection module, the output, input resistance and gain signals are calculated by the single chip microcomputer.

2) NETWORK ANALYSIS UNDER TEST
The network under test is a single-tube (C9013) amplifier circuit, which is a Q-point stable partial voltage bias circuit, as shown in Figure 7.  (1) The measured beta = 172. Using static point analysis: (2) The theoretical magnification, input resistance and output resistance are given by: VOLUME 8, 2020 (26 mV at room temperature), (3) In the measurement process, any amplifier circuit can be equivalent to a two-terminal network. A, R i and R o represent the magnification, input resistance, and output resistance, respectively. From Figure 8, the twoport network has: where A, R i and R o represent the magnification, input resistance, and output resistance, respectively. Figure 9, where R s represents the source resistance value and u o , a test value.

IV. SUMMARY
In this study, we designed a type of intelligent circuit characteristics tester, to reveal circuit problems in a timely fashion, thus improving electronic output. Our design has many shortcomings, and further research is needed to (1) Supplement this research with more data to further improve the system.