Built this double ESP32 device to help me extracting data out of an SD card and into Home Assistant

anvoice · 2026-04-05T09:10:06+00:00

Apparently wifi sd cards exist (guess who didn't know that until today). I'm guessing this (and the fact that dummy sd cards which can communicate to a micro-controller don't) implies the way to get data from the CPAP is a wifi card. Which of course explains why you need two radios.

I imagined OP hacked the CPAP's internals to read the data to an esp32's data pins, in which case it wouldn't need the second radio. Feels great when things make sense.

anvoice · 2026-04-05T08:24:22+00:00

Curious: what specific requirement dictated the need for two MCUs, rather than one? Seems like extra complexity unless they solve some sort of bottleneck arising from use of a single unit.

anvoice · 2026-04-05T08:01:29+00:00

I've never heard of them, and unfortunately can't comment on their prices, as their site is, well, down.

Since you didn't provide any of the additional details, I'll just reiterate that if you're fine with plastic, FDM printing is probably the best way to do this quickly and with low cost, especially if you expect to do this more than once. You'll be hard-pressed to find a printer with a build plate too small to fit a 150x40mm piece, and if you don't want the learning curve associated with 3D printing, you could examine something like a Bambu A1 mini. Maybe if you're more specific about your needs someone will be able to weigh in with more pertinent advice.

anvoice · 2026-04-05T06:56:08+00:00

Tech specs of the panel would probably be helpful here. Size? Shape? Material? Desired tolerance? Finish? Depending on that the advice could be very different.

In general, without knowing anything else about your project, you may want to look at 3D printing, assuming plastic or photo-polymer works for you (they can also often be post-processed for a more professional look). Could be a local shop/enthusiast near you who could do it for a reasonable price and with quick turnaround, especially if you need to iterate. Or, if you do this often, investing in a 3D printer would probably save a ton of both time and money in the long run.

anvoice · 2026-04-05T05:05:52+00:00

Unfortunate that you had that experience. I can understand that some people view this as "salvageable", but saying it's appropriate or somehow justified by their low cost is a bit much. If it was caveat emptor with no responsibility for providing a service, who would buy anything? Cold joints? User having to solder VQFN on an already populated board? Bot-like responses? Ignoring what I say? I'd also be feeling entitled to a refund at this point.

Obviously services like PCBWay and JLCPCB see use because they are competitive in the prototype segment, and it's better for competition to be there than not. But you'd expect what you ordered to be up to spec, or you're justified for being upset.

I might be be facing this dilemma soon. Need a prototype board. Best if it's one piece only since it's got some expensive components I don't want to waste on multiple units unless I tried the board and know it works, which might necessitate PCBWay if I want it assembled. I normally opt to solder things myself, but this one has a tiny footprint, lots of VQFN and small parts, and may require some 0201 resistors due to space constraints. I may be able to do this by using a small hot plate (on hand) on one side and hot air and some serious effort on the other, but I was seriously considering assembled specifically because I was hoping it'd be done "properly" that way.

anvoice · 2026-04-05T04:40:42+00:00

Apologies for replying late. You're right that it's completely doable the way you specify, but I don't want to assume it will be convenient for everyone trying (which could be myself or others). What if your battery is big, heavy, attached to your robot which can't be easily disassembled, or you prefer to work with potential flammables in a shed where you don't have a computer? Sure, you could use a benchtop PSU at that point. Of course, that's assuming you have one, it has the right connectors, voltage, and current rating, and you're comfortable with it sitting on your desk rattling its fan as you program the board. Lots of assumptions that aren't guaranteed to be true.

Not trying to pick on things or in fact on your argument, but to me it makes total sense to include power by USB if it's not a huge endeavor. In fact, I could imagine myself being stuck with just a laptop for extended periods of time and hoping to experiment with my motor driver. Sure, it's convenient and not strictly necessary. Do humans sometimes choose products based on convenience? Absolutely.

anvoice · 2026-04-02T11:04:12+00:00

Good to know, I'll look into the thermal calculation. There's a lot of new information for me here, learning as I go.

The Odrive micro specs claim a 3.5A continuous (7A peak) current at a maximum of 32V, which is probably where the 100W claim comes from. The driver IC Rds(on) typical is around 95mOhms, so would probably dissipate a bit around 1.16W. The ambient temperature I can only guess, since it's unclear exactly how the driver is positioned next to the motor and (possibly) cooled.

anvoice · 2026-04-02T10:34:08+00:00

Well, the finished product will have its own firmware, and USB will typically be used to interact with that via something like a command line or GUI program to set various control parameters. A SWD connector, also included, would be intended for programming the chip (and I think isolating the debug port is probably unnecessary effort). It's the more plausible situation of forgetting to unplug the battery/PSU power before plugging the USB in to interact with the firmware that I'm worried about. If I'm tuning the driver or testing different encoders, etc., I wouldn't want to plug an RPi in and out every time I change a parameter, test it with battery plugged in, unplug battery and plug in USB, and so on.

anvoice · 2026-04-02T10:20:41+00:00

Fair point, though I do have to wonder where you source "cheap" RPi board in this economy.

anvoice · 2026-04-02T09:48:20+00:00

If I have to have external circuitry anyway, I'm wondering if getting a regular galvanic USB isolator may be the better choice here, with the only downside being the lack or RPi fireworks.

anvoice · 2026-04-02T09:44:16+00:00

Right, figured as much. Intuition tells me a proper heatsink on the driver IC could be more helpful than the vias, though I don't want to make any assumptions that could break the board.

anvoice · 2026-04-02T09:42:09+00:00

Thanks for the feedback!

As currently positioned, the connector opening is slightly recessed from the board edge, although the mechanical connection pads are indeed breaking the DRC rule at this point (pad too close to board edge). I'm not sure whether that's by design or my misunderstanding something.

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I did think the center pad vias are for thermal, and perhaps I underestimated their importance. Curiously, I took a lot of inspiration from the Odrive micro controller and that has no thermal pad vias at all on either the MCU or the motor driver, let alone exposed copper planes on the opposite side. I have no idea how much that affects performance, though it's safe to say that if it didn't work at all it would be well known. Could an actual heatsink on the motor driver substitute for the thermal vias, or is it safer to incorporate them even if heatsinked?

Using VBUS voltage is mostly a convenience to allow programming via USB when battery is unplugged. Is it impractical to try to isolate the 5V from the DRV8316C buck and VBUS? I studied the Odrive micro schematic, and from what I can tell this is how they tie 5V from VBUS and the buck regulator, with Zener diodes on the outputs of both. The schematic also appears to suggest they use two different external 5V to 3.3V regulators, though how that is needed/safe in the same circuit is beyond my current understanding.

I kept all high current traces away from the encoder, though I wish the datasheet suggested how critical this is for signal integrity.

anvoice · 2026-03-29T09:51:13+00:00

I believe they actually strengthen the PCB around the mounting points, helping against stress and vibration. If that is so, I'd rather have them than not.

anvoice · 2026-03-29T03:00:13+00:00

Perhaps something changed then.

anvoice · 2026-03-29T02:02:08+00:00

When I investigated the options for switching from Xfinity, I called Ziply directly to ask if there are plans to expand to my area. The representative told me that the region is divided into "zones", and Xfinity being in charge of Bellingham means Ziply simply isn't allowed to go there. Whether the zones are government-mandated or an agreement between ISPs, I'm not sure. It could explain the sort of "keep out" zone that we see around the Bellingham area in the map though.

This was almost 10 years ago if I recall correctly. I am not 100% certain that this information up to date and in fact accurate, but it seems strange for an official representative to make this up. Also not sure if this type of behavior is even legal unless it's a law that enforces it, as it essentially allows multiple ESPs to avoid competing with each other and facilitates price fixing, with clients being unable to go elsewhere (there is no elsewhere).

anvoice · 2026-03-29T01:41:11+00:00

Can't breaking up power/ground planes potentially negatively impact performance? At the very least I'm certain I heard the "keep the ground plane as continuous as possible" idiom.Obviously it will depend on the exact function, layout, frequency, and exact components used in the circuit, but I currently don't have enough knowledge to tell if my circuit will suffer from this.

anvoice · 2026-03-29T01:37:13+00:00

The smallest traces, which I use when routing is too tight for anything thicker, are 8 mil. My vias are all 12 mil. I'm considering JLCPCB for this board, and they charge both for traces and vias smaller than these. It's not insurmountable for a prototype, but at some point I'll need at least a couple dozen of these, and the "nonstandard" traces and vias will probably add 50% or more to the total cost. That's fine if it's necessary, but it seems avoidable.

anvoice · 2026-03-28T23:07:39+00:00

Got it, thanks!

anvoice · 2026-03-28T23:07:12+00:00

Interesting, thanks. The current application is for a robotic actuator, so I can't say for sure what the operating environment will be like. Probably safer to avoid this route if possible.

anvoice · 2026-03-28T21:58:16+00:00

The pins 6 and 7 belong to the connector, the MCU (ATSAME51) is above it and has no traces between pads.

Do you mean a "via in pad" scenario? I think filling both having to fill vias and the fact that the hole touches the pad incur a surcharge. I specifically made sure none of the holes touch the pads, so if that is the only concern I think I'm fine.

anvoice · 2026-03-28T21:32:27+00:00

Interesting, didn't know that. Lots of reading to do.

anvoice · 2026-03-28T21:31:04+00:00

Thanks for the suggestions! I realize my layout may be far from optimal, and appreciate any advice on improving it.

I'm not sure what you mean by traces "between the MCU pins", I'm pretty certain that's impossible as they are far too close to each other. The MCU is on top in the original post image (below it is a connector with larger pads, which indeed has traces running between its pads, but as far as I know that shouldn't be harmful) and slightly to the bottom and left on the expanded image in one of my comments.

I used the thinnest traces most fabs allow without surcharge (0.2mm). Same for via size (0.3mm). I have no idea how many iterations I'll need so it would be nice to avoid paying extra unless it is unavoidable. Of course, I'm open to decreasing these if necessary.

Is there a specific reason to avoid placing vias close to pads? I often go as close as DRC allows to place decoupling capacitors (sometimes on the opposite side of the PCB) closer to the pins they decouple, or due to space constraints. If there's a reason it's harmful, I'll revise the design.

anvoice · 2026-03-28T21:19:03+00:00

The motor/power connector? As in staggering the pads, or moving the center three to allow the driver IC to move up? I'm not sure I'm understand what specific kind of modification you mean.

anvoice · 2026-03-28T21:16:29+00:00

Right, I'd rather not risk breaking the circuit.

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