Simple Digital Oscilloscope – Based on the Hardwood Classroom Open Source Project

The EDA Instrumentation Training Camp
for beginners features a replica of the Hardwood Classroom AFE03 oscilloscope signal source extension: https://oshwhub.com/damihuang/AFE03/.
As an instrumentation major, I was surprised to see that JLCPCB was offering an instrumentation design program. Having some free time after securing my postgraduate studies, I participated in JLCPCB's EDA training camp for the first time. I figured oscilloscopes were highly practical and didn't seem too difficult, so I chose it without much thought.
During the design process, to better utilize my PCB redesign skills, and considering the high price and redundant design of the Hardwood Classroom H750 development board, and fearing I wouldn't be able to rewrite the software within a month, and given my lack of experience designing microcontroller core boards directly, I decisively chose an open-source core board that also uses the STM32H750VBT6.
Therefore, I drew the core board's components and packages in EDA, directly referencing the Hardwood Classroom's pin layout for software compatibility.
 
PCB Design Process:
1. The schematic
is based on the open-source schematic from Hardwood Classroom, with all components replaced by standardized components available from LCSC. Since a custom core board was used, the original buzzer from the development board was added. Other parts are largely replicated from the Hardwood Classroom schematic. Note that the LDO pins of the power supply are prone to bridging, so an extra board was made for this purpose.
2. The PCB
layout is basically based on Hardwood Classroom, but for aesthetic purposes, a top cover was added, and the input/output ports and buttons were moved to the side. A double-layer board layout was also attempted, placing the main components on the back of the motherboard, while the front retains the header, rotary encoder, and reserved space for the screen. The component layout was unexpectedly compact; keeping all signal lines on the back layer made this one of the most challenging routing projects in my design career. Placing surface-mount components on a single plane also facilitates soldering.
3. Components and Soldering:
STM32 Core Board:
2.8-inch TFT Screen:
All other components were purchased from LCSC.
Soldering was relatively easy. First, apply solder paste, then place all the surface-mount components and heat directly on a hot plate. For any
solder joints, use a soldering iron to adjust them. However, note that there are several NC components in the schematic that don't require soldering.
4. 3D Shell
: This was my first time using the shell design provided by LCSC EDA. Surprisingly, it was quite simple and convenient to design. However, since it's designing a 3D structure on a 2D plane, the 3D view reference wasn't very useful.
I managed to get it done, albeit with some difficulty. For the printing material, I chose the most expensive transparent resin for aesthetics. Surprisingly, the final product from 3D Monkey turned out quite well, with very high transparency. The screen was directly fixed with hot melt glue, but the aged yellow glue was unsightly…
5. Software and Programming
: Due to time constraints, I directly copied the project files from Hardwood Classroom and compiled them using Keil MDK to generate the project's HEX file.
Since I used the STM32H750 core board and didn't have an STLink programmer, I used the built-in DFU programming function. I used DFU File Manager to convert the hex file to a dfu file. By connecting the BTO pin to 3V3 to start DFU Mode, connecting the core board to the computer, and then downloading via DfuSe Demo,
the programming process was surprisingly smooth. After the program was written, waveforms were displayed directly, and the input of each HMI button and knob worked without issue.
 
Expected performance parameters:
Analog input
channel count: Synchronous dual-channel; Sampling rate/bandwidth: 2MSPS/100KHz;
Input range: ±10mV - ±15V;
Input impedance: 1MΩ;                                           
Analog output
channel count: 1; Output signal waveform types: Sine wave, square wave, triangle wave; Output sine wave frequency: 1Hz - 20KHz; Output range: ±10mV - ±10V;
Output impedance: 50 ohms;
Output current capability: ±10mA;
                                     
Finished product effect: