#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
The main issue we have with I2C is capacitance. You can mitigate this with lower...
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
Can I ask why you’re choosing to put this all on one board? I expect you’ll be d...
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
Almost all of the sensors use I2C and most are Adafruit breakouts connected via ...
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.
Feel free to update me after you complete the routing and I can give additional feedback
vagrant kestrel
Well I've used the main ICs already, so I can keep most of my code. But a lot of the hardware is new.
Here's a PDF export of all the layers. Routing got a bit messy towards the end, I'd say, because this thing is really tightly packed. But at least I don't have any DRC errors that I'd consider important.
elfin flume
Wow, that’s really packed in there. I’m glad you got it all to fit on one side
I don’t see any glaring issues, though it’s hard to tell from the PDF. Your routing seems reasonable
Looks like the traces are pretty close on one of the mounting holes. Do you have nylon washers to protect the traces from the screw heads?
vagrant kestrel
I can upload the project files as well, that should make things easier to see. Wasn't really sure what the preferred method is for showing this.
The holes are just best guesses right now. Once I have their exact dimensions modelled in CAD, they will probably more a millimetre or two and then I'll give them as much room as I can.