North China Electric Power University 14th Electronic Design Competition 2021

1. Overall plan and design ideas:

This circuit scheme is based on Arduino master control and uses DAC to measure the input and output port voltages to obtain parameters such as amplification and input and output resistance. The sinusoidal signal sends out the PWM waveform through the arduino , and then is filtered by the LM324 . The microcontroller obtains the cause of the amplifier circuit failure by comparing parameters such as input and output voltage and amplification factor between the fault state and the normal state.

In the measurement of the static operating point, we short-circuit C1 and C2 and assume i _cq =i _eq to measure the parameters of the static operating point.

In the measurement of input and output impedance, the input and output ports are divided by the series resistor R , and the resistance of the input and output ports R ₀ = is obtained by comparing the voltages U ₁ and U ₂ before and after series connection .

In the measurement of open circuit and short circuit, since the voltage values ​​and amplification factors of the input and output ports are different in different faults, the cause of the fault can be inferred by measuring these parameters.

2.Circuit part

This circuit is the amplifier circuit provided in the question. We have conducted port extraction processing on this circuit to facilitate short-circuit and open-circuit operations on various electrical devices. Where H2 is the input port and H3 is the output port.

The first part is the LM324 op amp filtering part. This circuit inputs a PWM waveform and outputs a sinusoidal signal to provide a signal source for the amplifier circuit. The second part is the voltage stabilizing part, which steps down the 12V DC power supply into a 5V DC power supply and has a voltage stabilizing effect. The third part is the microcontroller arduino and 12864oled display part for data processing and result display.

Since the arduino uses a 5V power supply, a buck module is used to reduce the voltage. This microcontroller can only measure voltages below 5V , so two 1K resistors are used to divide the voltage, thereby increasing the range of the microcontroller to 0-10V .

3. Simulation results

It can be seen that the lower limit frequency is about 15.375hz and the upper limit frequency is about 35.436mhz. The working bandwidth is 35.436mhz.

Magnification is approximately 9.92 times