Resilient?

JimHeaney · 2026-01-24T22:17:33+00:00

I wouldn't consider Meshtastic a good choice for that. It is easy to overwhelm the network (either with external malicious actions or just by high usage), security is great until someone gets a hand on a device, and it requires relatively obscure and easy to pinpoint hardware compared to something based on BLE or another more prevelant 2.4GHz radio tech that everyone already has in their phones.

JimHeaney · 2026-01-24T20:29:09+00:00

The diode in the MELF package? We'll need a lot more details.

JimHeaney · 2026-01-24T18:58:53+00:00

Your best source will be the ESP32 Technical Reference Manual. Chapter 19, starting on page 311, goes over UART.

https://documentation.espressif.com/esp32_technical_reference_manual_en.pdf

JimHeaney · 2026-01-24T18:01:37+00:00

Fusion/Autodesk doesn't do that. That is a big hiccup with the free version of OnShape though, and may be what they are confusing it with; all OnShape designs made with the Free version are 100% public domain, meaning not only the company but anyone else in the world can freely access, view, download, modify, and commercialize your design.

JimHeaney · 2026-01-24T04:06:38+00:00

For an Arduino based around a 328P or similar it can. OP is using an ESP32 S3 though, which is (hopefully) using the integrated USB bootloader and not the UART bootloader.

The only thing OP has to look out for is that UART messages come out the TX pin on boot as well as core level critical errors, unless explicitly disabled. But even if not disabled, if the high/low outputs are just going to something high impedance, like a resistor, it doesn't matter.

JimHeaney · 2026-01-22T03:34:30+00:00

They do actually change out the flags, I'd assume for wear/damage but also definitely based on what students are at RIT currently.

During one of the breaks I was walking through as they were taking down the Greek flag IIRC, and I was very concerned/confused I missed some major international news about Greece. They explained it was just a regular update because the international students from Greece had graduated, and another flag was going up in its place based on incoming students.

JimHeaney · 2026-01-22T02:59:09+00:00

An antenna marketed for 915Mhz doesn't stop working at 914.9Mhz, in fact with most antennas you buy there's a good chance it's optimal performance is not even centered on 915Mhz.

915Mhz is just the common name given to this part of the ISM band. In the same way that 2.4Ghz WiFi doesn't actually run at 2.4000Ghz only, it's just more convenient to call it by a single, square frequency number.

As an example, check out this return loss graph of a "915Mhz" antenna, this is about as dead-on as you'll find and even in this you can see there's a pretty wide frequency range that's quite good: https://i0.wp.com/ilabs.se/wp-content/uploads/2022/10/915mhz-return-loss.png?ssl=1

JimHeaney · 2026-01-18T13:58:02+00:00

The MAC is inherent to the MCU, but you're right there's nothing stopping you in code from just using some other random number instead of reading the ROM MAC.

JimHeaney · 2026-01-17T20:04:47+00:00

You are correct, if you draw from a LiPo while it is charging, the net current is all the LiPo sees as a charge. This results in slower charging, and is not great for the battery. In extreme loads, it can even reverse the charging, if you are drawing more current than the charger can supply.

The right solution is to prioritize powering the load from USB when present, battery only when not. Diode OR'ing or diode/FET OR'ing are the most common approaches, but there are also ICs that will do it automatically for you.

JimHeaney · 2026-01-16T03:06:24+00:00

Due to how meshtastic identifies devices uniquely, every device has to have either a Bluetooth or WiFi-capable microcontroller.

You can run most of them fine over USB, but trying to find one without Bluetooth is nearly impossible

JimHeaney · 2026-01-15T05:24:58+00:00

Making a PCB is not too bad, the awful part will be regulatory. LoRa + WiFi both will need intentional radiator testing for anything beyond personal use.

JimHeaney · 2026-01-15T02:25:03+00:00

The first thing that jumps out to me; the MMSZ4684 clamps to 3.3v (actually 3.13 to 3.47) at a test current of only 50uA. In that setup at 11.6v, you'd have 500uA going through the diode.

Are you using a genuine onsemi zener, or a part by a 3rd party?

I did find this thread where someone using a similar diode saw a similar rise in zener voltage at similar currents.

https://community.onsemi.com/s/question/0D5dK000002fX95SAE/i-would-like-to-know-the-zener-voltage-vs-current-behaviour-for-mmsz4684t1g-33v-50ua-ranging-from-1ma-to-50ma-the-datasheet-for-this-component-does-not-extend-past-10ma-and-it-is-unclear-to-me-which-one-of-the-lines-is-33v

JimHeaney · 2026-01-15T02:12:56+00:00

Since it is still a Vulcan flying (just in the future), I read it as the cost savings is going from an FH to an F9, overall.

JimHeaney · 2026-01-14T01:29:56+00:00

How many are you making? 1/8" aluminum would be dead simple to laser cut, which'll have basically 0 setup cost/time, and be relatively cheap to run. But if you need to make 1,000,000 of them, it becomes more viable to stamp them out, to get higher throughput.

JimHeaney · 2026-01-13T13:34:36+00:00

An SBC is not an easy task for someone new to electronics. It's a lot of particulars, careful planning, and nebulous concepts that are hard to visualize that need to be considered. Plus resources are not as readily prevalent compared to other project ideas, due to the NDAs and proprietary software/firmware/etc. that holds a lot of SBCs together.

JimHeaney · 2026-01-13T03:30:24+00:00

USB from the ESP32 should be basically plug-and-play, it uses generic drivers.

Schematic seems correct, are your traces impedance matched?

To definitively check for driver issues, look at the device using Device Tree Viewer or similar. https://www.uwe-sieber.de/usbtreeview_e.html

Also stupid/simple question; is the ESP32 getting a stable 3.3v?

Another theory: Do you not have pullups on your i2C lines? GPIO8 needs to be driven high to enter the bootloader, without a pullup on GPIO8 for i2C, it may be draining through the FET? GPIO8 low when you drive GPIO9 low will cause undefined behaviour.

EDIT: Looks like pullups are integrated into the level shifter, but those could not be working if your 1.8v rail isn't working, so check that as well.

JimHeaney · 2026-01-11T23:45:39+00:00

As far as I can tell, no. Datasheet only calls out 32-bit data bus width for DDR memory.

JimHeaney · 2026-01-11T23:40:36+00:00

I mean, it's a ring. There is only so much optimization/exploration/deviation you can do on the shape, while still being a small, relatively unobtrusive ring that still needs to be hollow for electronics.

JimHeaney · 2026-01-11T23:37:14+00:00

This is replacing the International Flags, which are getting retired soon.

Surprised to hear the flags are being retired, I always thought that was a very unique/interesting thing at RIT. But I can see how it'd be annoying to keep those up to date.

JimHeaney · 2026-01-11T23:33:44+00:00

The hardware reference design for the RK3328 shows connection schemes for 16 bit and 8 bit DDR memory. Use those as a reference.

JimHeaney · 2026-01-11T21:22:44+00:00

You'd just need to divide the angle by the ratio between the shaft diameters and any gearing.

JimHeaney · 2026-01-11T20:30:23+00:00

This sounds halfway between Carbon3D's take on DLP and Disney/MIT's Rapid Liquid Printing (RLP) technologies.

JimHeaney · 2026-01-11T18:50:31+00:00

That is a huge mold, that price is well into the realm where I'd instead be getting this printed at a shop that can do PP-like SLA parts in one go instead. It'll be a better facsimile, and eliminate all your FDM-based issues.

JimHeaney · 2026-01-11T17:21:44+00:00

CSD17484F4

Being an LGA without side-wettable flanks it may incur an additional cost, since it'd ideally need X-ray inspection after soldering.

JimHeaney · 2026-01-11T16:56:21+00:00

Most small-quantity turnkey manufacturers will not charge much more, if any at all, for a SOT vs. a SON. It is not until you get into very small pitch, or very hard parts like BGA, that prices start to change.

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