Complex PCB

[elfin flume]

Complex PCB

Yes, this is too tight for a two-layer board but should work for a four-layer board

The main issue we have with I2C is capacitance. You can mitigate this with lower clock speeds or lower value pull-up resistors

SPI shouldn’t have issues up to 1MHz but you might run into problems around 10MHz

There is a lot going on here, with noise sources from the buck regulator, LoRa, SPI, and the stepper drivers, but low-noise requirements for the ADC and whatever other sensors you have

Can I ask why you’re choosing to put this all on one board? I expect you’ll be doing a couple board spins to get everything right, which is going to get expensive

[vagrant kestrel]

Thanks for having a look 🙂

[vagrant kestrel]

Almost all of the sensors use I2C and most are Adafruit breakouts connected via StemmaQT. I believe Adafruit's boards always come with pullup resistors, so that should help? I've only got one 10K for each line on the PCB right now. Should I put down more and maybe spread them out?

[vagrant kestrel]

Well partly this is because I think it's the best approach for the project overall. Splitting the PCB would require different mounting, which means more printed parts and a bigger project, but also more wasted space for connectors, screws and board edge clearance. I don't think I have that much space left, I'd rather have good connector placement and legible silkscreen.

But on the other hand, I honestly just want to try it like this and reach a personal milestone. I'm having an blast with the PCB design and SMD soldering is an absolute revelation. I think I'll even get myself a stencil and a reflow oven for this one.

The last iteration of the project (which worked, just wasn't happy with the mechanics in the end) had a similarly tight PCB, but with much fewer components. Instead, it had a lot of Adafruit breakouts stuck on socket headers, which I felt was wasting a lot of space, because these breakouts usually come with a regulator, level shifting and lots of broken out pins I don't need.

[elfin flume]

Keep the 10k for now, you can change to 1k later if needed

It sounds like you’ve already prototyped with these components and now want better packaging.