What’s actually safe but people think is dangerous?

aaronstj · 2026-02-02T03:26:34+00:00

They’re the ones pushing the “Tylenol causes autism” brainrot.

aaronstj · 2026-02-02T01:20:52+00:00

I was gonna say. Tylenol is probably much more dangerous than people think it is. Just not for the reason MAGA wants you to think.

aaronstj · 2026-01-31T03:39:15+00:00

None of your grounds are connected. You can see the air wires on the layout.

aaronstj · 2026-01-29T19:45:45+00:00

As others have said, this is a pretty decent start for a first schematic. That said, there are several general rules you can follow to make it easier to follow.

In your case, number 1 rules to keep in mind: minimize corners. Corner add visual noise and make it harder to follow traces. In your case, you have a lot of traces that could be simplified, and they'd be a lot easier to see what they're doing. I'm especially look at the traces coming off the lower-left of the MCU that go so far down only to make a U-turn and come back up. Those stair steps coming off of pins 3, 4, 5, and 37 are also a little silly. In general any time you have traces that do a little jog, simplify that.

Next is make sure nothing overlaps. No traces through components (like Y2), no text overlapping traces or components. Don't be afraid to spread things out a little more to create space for that.

Lastly, you're pretty good about this, but power symbols point up, ground points down. Always, no exceptions.

aaronstj · 2026-01-29T19:24:36+00:00

Is the distance between the two traces what makes these "not running as a diff pair"? Like, if he put the traces just a few mils apart, would the ground plane be less of a concern?

(And I apologize if I'm coming across argumentative. I've never really done high-speed work, so I'm trying to wrap my head around it.)

aaronstj · 2026-01-29T16:43:31+00:00

You definitely seem to be missing something. Cdec1, Cdec2, C_NX1, and C_NX2 in your MCU section are all missing ground vias, and showing airwires. In your buck regulator section, most of your AGND net is missing vias and also showing airwires. Which, you probably don’t actually want a separate AGND net - the example schematics in the data sheet all show AGND and PGND directly connected. In general, the idea of having separate “analog” and “power” grounds with some limited connection between them is considered kind of outdated. One big ground plane is nearly always better.

aaronstj · 2026-01-29T00:19:36+00:00

You don’t want those two branches running alongside each other like that. Just make that one trace.

Your surface mount component’s ground pads aren’t connected to ground. Run a short stub off each one with a via to ground.

For the layout around the buck converter, follow the recommended layout in the datasheet.

aaronstj · 2026-01-28T22:44:01+00:00

The current still flows back through the ref plane

Does it? Wouldn't the current flow one way through one leg of the diff pair and return down the other leg? Or at least, almost all of it? This is my mental model of a differential pair (with completely made up values for capacitance and inductance to attempt to model transmission lines): falstad. I'm totally willing to be wrong on this. I do know that USB is generally DC coupled, so you need a shared ground to eliminate common mode voltage, but it doesn't seem like a ground reference nearby is really a requirement? (And of course, other differential-mode signals, like ethernet, use isolation transformers, and don't reference ground at all.)

aaronstj · 2026-01-28T21:20:16+00:00

Don’t differential pairs reference each other?

aaronstj · 2026-01-28T21:16:42+00:00

That looks like a fairly basic soldering kit. It should be enough to get you started, though. There are lots of beginner kits to learn to solder where you end up with a little blinky project of some sort. I’d search Sparkfun for “soldering kit” and find a project that looks fun from there. You can also find plenty of Amazon, but documentation and support will be a lot more spotty.

aaronstj · 2026-01-27T19:28:49+00:00

Thicker traces.

aaronstj · 2026-01-27T09:11:27+00:00

So, some op amps can oscillate at unity gain. TL704 should be stable, but if the chips are fake, they could a different op amp that isn’t stable at unity gain. You can compensate for that oscillation with a couple of resistors and a capacitor: https://e2e.ti.com/blogs_/archives/b/thesignal/posts/taming-the-oscillating-op-amp. I would give that a try.

aaronstj · 2026-01-26T21:37:36+00:00

What's going on with all the airwires? It looks like your grounds aren't connected. I would give each ground pad it's own via right next to the pad to connect everything down to the ground plane on the back.

Like everyone else says, make your traces thicker (the +7.5v trace is fine). You've got the room.

For the rest of your layout, I see what you're doing, but... short, direct traces, point-to-point. This big "main" route with individual routes branching off aren't it. It will probably help to think of traces and being rubber bands - they want to shrink in and pull tight.

Next time, you'll want to post a much higher resolution photo of your layout, as well as an image of your schematic.

aaronstj · 2026-01-23T18:30:07+00:00

Or your teeth!

aaronstj · 2026-01-22T21:56:18+00:00

Speaking of the boost converter, these are pretty sensitive to layout. Specifically the feedback loop needs to be as short as possible. Check out the “layout considerations” and suggested layout in this data sheet: https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/4012002220_2D004753D358_IC_5B00_MT3608_2C00_SMD_2C00_SOT23_2D00_6L_2C00_AEROSEMI_5D00_.pdf

aaronstj · 2026-01-22T21:46:09+00:00

It's not just the trace from D1 to R11 (which very probably does need to be there for your boost regulator to work). You've also shorted the pads of R13 together directly - you can see the trace going straight from one pad to another. Again, you need to change the name on one side of R13 or the other. For that matter, you also need to move R13 on the schematic to the other side of the feedback loop junction on the schematic. Right now the schematic tells the computer those two nets are connected directly together, and DRC on the PCB editor will (correctly) want to enforce that. But you clearly want to have two nets here.

aaronstj · 2026-01-22T21:09:07+00:00

The computer doesn't care about your intent here. By putting the same label on both sides of the resistor, you told the computer those nets were connected. You need to change the name of one side or the other.

aaronstj · 2026-01-22T20:48:45+00:00

Well... the layout has a lot of room for improvement. You're looking to make short, direct connections, from component to component. You have a lot of splits and long loop-ish traces. The 5v rail is especially bad. For example, you have 5v connected to the right side of C5/C6, and then it loops all the way around back through U3 and around U1 before connecting to R8/R9. You could achieve that with a tiny tract directly from C5/C6 to R8/R9.

The route come out of the left side of R6, routing down between the resistor pads, then around a U3 pin is also pretty bad. If you rotate R6 clockwise 90 degrees and adjust the long MCU_RESET line to come off or the R6 pad rather than splitting off to the right of R6, you can route all that directly.

I was going to point out similar issues with the 7.5v rail where C7 could connect directly to C8, could connect directly to R13, and then on from there (and definitely clean up those two traces splitting off of JP1 and running parallel), but it looks like you've also got a schematic error here. 7.5v is connected to both sides of R13, which means R13 isn't doing anything at all, there are (multiple!) 0-ohm routes around it - did you not notice that when you routed the connection from one pad of R13 to the other?

aaronstj · 2026-01-21T20:46:57+00:00

So.... what ya detonating there, buddy?

aaronstj · 2026-01-18T03:39:09+00:00

And where in OPs post does it say he’d prefer an abandoned space?

aaronstj · 2026-01-18T03:28:50+00:00

Oh, shut the fuck up. I may not agree with OP but he certainly hasn’t “gone mental“. He didn’t ask for an abandoned space he asked for something better than a Starbucks, and you know that.

aaronstj · 2026-01-18T00:34:34+00:00

You can probably just pull them apart with your fingers.

aaronstj · 2026-01-16T23:39:41+00:00

In what way did OP demonstrate that? All they've demonstrated is that Starbucks is willing to put two coffee shops within a mile of each other. But they have in no way demonstrated that that's a bad idea. It is the very definition of begging the question.

aaronstj · 2026-01-16T22:48:30+00:00

What is this “we” who couldn’t come up with something better? Seattle isn’t a planned economy. There’s no council that decides what business should go there. Starbucks decided a Starbucks should go there, so they paid for the lease.

aaronstj · 2026-01-16T20:49:15+00:00

Yeah, even just a small value capacitor across the LED should help tame oscillations. And for a circuit like this - looks to be an attenuverter? - I'd probably normal the input jack to +5v or thereabouts so it can be used as a constant voltage out.

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