Simple Oscilloscope

JLCPCB, Hardwood Classroom, and Wuhan Xinyuan Semiconductor jointly organized this LCPCB training camp. First of all, I would like to thank them for providing the opportunity and platform, which allowed me to learn the entire process of instrumentation circuit design. I also met many like-minded friends who provided assistance during the replication process.
 
The software portion of this project was provided by Hardwood Classroom, while the hardware portion was a replication of the Hardwood Classroom project with some minor modifications.
Circuit References:
[Hardwood Classroom] AFE03 Oscilloscope Signal Source Expansion Board https://oshwhub.com/damihuang/AFE03
 
Hardwood Classroom Knowledge Base:
https://www.yuque.com/yingmuketang/01/tza1xu0gk3ps5dac
 
Hardwood Classroom H750 Core Board:
https://item.taobao.com/item.htm?spm=a21n57.1.0.0.9895523cQ7Tr1r&id=668498418826&ns=1&abbucket=10#detail
 
Principle Part:
Signal Conditioning Circuit:
Analog Input Channel Introduction:
Includes signal conditioning implemented by resistor voltage divider and operational amplifier, and square wave output implemented by comparator (for triggering and frequency measurement).
INA, INB: Input terminals of the oscilloscope. The STM32H750VBT6 outputs analog signals that connect here. A 1MΩ input impedance is achieved through a series resistor voltage divider. Direct connection or 1/20 attenuation can be selected.
 
gain: Selector switch, choosing between a direct signal or a signal attenuated to 1/20 to enter the first-stage non-inverting amplifier. The non-inverting amplifier performs two functions: shifting the signal by 1.65V and amplifying it by a factor of 2 through a bias voltage, ensuring the input ±15V falls within the 0-3.3V range.
 
For the relay section, since the model was not yet determined when the schematic was drawn, pin headers were reserved for selecting the relay power supply.
AnalogA, AnalogB: The amplified and shifted analog signals from the non-inverting amplifier are connected to the STM32H750 development board and enter the H750's ADC.
TrigerA, TrigerB: AnalogA, AnalogB, and the DC reference level (generated by one of the H750's DACs) pass through a comparator to generate a square wave signal, which enters the STM32H750's timer for frequency measurement.
DAC_OUT2: DC reference level, output via the internal DAC2 configured by the STM32H750.
 
Analog output channel description:
Includes signal conditioning implemented with resistor dividers and operational amplifiers, and a square wave output implemented with a comparator (for triggering and frequency measurement).
The STM32H750's DAC1 output ranges from 0-3.3V.
A second-order RC filter implements a low-pass filter function.
A resistor divider and buffer convert the 5V input to a low-impedance 2V output, which is then amplified by -5 times for signal shifting.
The output amplifier performs two functions: first, it amplifies the non-inverting input by 6 times; second, it shifts the amplified signal by -10V before outputting it, calculated as Vo = -10 + 6 * Vi.
 
 
Functional testing
required a dual-channel oscilloscope input of

±10V, 2MHz sampling rate or higher, 20kHz bandwidth, with a peak-to-peak measurement error of no more than 5% for sine waves.
Range switching
was smooth with no noticeable triggering, and
the frequency measurement error was no more than 5%.

A single-channel oscilloscope

output showed ±4V peak-to-peak value, 20kHz bandwidth for square, triangle,
and sine waves, with peak-to-peak errors of no more than 15% for both sine and square waves. A problem

 
to be solved:
The power supply section used a domestic MT3608L, but during testing, it worked normally when the input voltage was below 5V. However, above 5V, the power supply was directly output most of the time, and the power chip did not work. Many methods were tried without success, and finally, the MT3608 was replaced, and the GND feedback resistor was removed.
 
Due to time constraints, the current project only meets basic functionalities and will be further improved later.