![Image 1 — [Schematic Review Request] STM32 based, Isolated PCB](https://preview.redd.it/ziw7pgaoshjh1.png?width=1254&format=png&auto=webp&s=158c11bcbaec25782829bdc479de54c75a338715)
![Image 2 — [Schematic Review Request] STM32 based, Isolated PCB](https://preview.redd.it/wslblgaoshjh1.png?width=1260&format=png&auto=webp&s=d51fd8e8ed6384dca584f69ec0be3ee9cf923a45)
![Image 3 — [Schematic Review Request] STM32 based, Isolated PCB](https://preview.redd.it/uqypygaoshjh1.png?width=1246&format=png&auto=webp&s=9587fc6a8fa759e6775a73150cbfb5cabe8fbd14)
[Schematic Review Request] STM32 based, Isolated PCB
Hi all, hope you're doing well. I'm a student, awefully inexperienced, and I'd really appreciate a professional set of eyes on this. I plan to post two more updates after taking in advice and be done with this within next 2 days.
The board takes RS485, a 0-10V input and a 4-20mA input from outside. It outputs a +24V-or-open discrete signal, a 0-24V output at up to 1A, and a switchable resistance across two terminals. The 1A is transient only, not continuous. STM32G474, 4-layer planned. Schematic only, no layout yet.
I've assumed you won't have time to open datasheets, so take it as given that per-component current and voltage ratings have been checked. My real questions are more fundamental:
- Will this circuit work at all? That's honestly my main worry.
- Are any of these blocks more complicated than they need to be? If something here has a standard, simpler solution I don't know about, I'd love to hear it. This is extremely important, i am out of ideas. Anything that doesn't break isolation and simplifies my desing would make my day.
- Is anything redundant, or doing a job something else already does?
I used an external SPI ADC instead of the MCU's own ADC, because the MCU sits on the isolated ground and I don't think an ADC pin can read a divider referenced to the other ground without shorting the isolation. And for the 0-24V output I ended up with an op-amp driving a BJT inside the feedback loop, because I couldn't find another way to get a controlled 0-24V while supplying 1A peaks. If there's a better standard approach to either, please tell me. I plan to do both debugging and uploading using STM by using boot and reset bottons.
I also have very no idea how to approach the PCB layout for this, especially the two ground regions, so any pointers there would help a lot.
Sorry if anything is unclear. This is my second or third PCB and by far the most complex thing I've attempted.