Classic case sharing: weak signal testing

This design hardware part mainly consists of signal amplification, AC-DC conversion, AD conversion, range conversion, single-chip microcomputer for data acquisition and data transmission, interface chip, serial port and PC. First, a window for controlling the range conversion and data display is generated on the PC; first, the range is selected according to the approximate range of the input AC signal voltage amplitude, and the information is sent to the MCU according to the selected range, and then strobed by the MCU. One of the three gear positions in the range adjustment section consisting mainly of CD4051 (CD4051 is actually an 8-channel analog switch. In this design, only three channels are actually used, depending on the resistance of each channel. Forming three measuring gears), the different magnitudes of the feedback resistors connected to the gated gears and the op amp OP07 constitute a positive negative feedback amplifying circuit, so that the amplifying circuit performs different magnifications on the input signals; The amplified signal passes through the AC-DC conversion circuit, and the AC signal is converted into a DC signal. The voltage is equal to the effective value of the AC signal. The DC signal is converted into a digital signal by the AD chip. The MCU reads the AD chip for data acquisition and then transmits it to the PC through the serial port. The machine displays.

Hardware design block diagram:

It can be seen from the schematic diagram that the measured periodic AC signal is first amplified by the op amp OP07, and the amplified signal is converted into a DC signal by the AC-DC converter AD637, then AD conversion is performed by the ADC0831, and the converted digital signal is transmitted by the single-chip microcomputer. The acquisition is performed, and the last sampled data is output to the PC through the serial port for display. According to the voltage range of the input signal, it needs to be separately amplified. This part mainly relies on the multi-way switch CD4051 which is programmed by the single-chip microcomputer.

Description of each main circuit

Signal amplification part: (Signal amplification part consists of op amp OP07 and multi-channel analog switch CD4051)

Commissioning results and error analysis

According to the above scheme, the detection circuit is debugged, and the input weak signal may be a sine wave, a triangle wave or a square wave, and the voltage range thereof is 10 μV to 5 V, and the frequency range is 10 Hz to 1 MHz. The debug data is shown in Table 5.1 below:

Analysis of debugging results: First, the main cause of error is that the input signal source will generate a small amount of ripple, and the accuracy of the OP07 itself will also affect the test results. Second, the voltage range of the input signal cannot exceed 4.16V. It is determined by the AD conversion chip itself selected.

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