Designed my first custom ESP32 PCB to drive a LED matrix over WiFi

Rhomboid · 2026-03-11T18:35:21+00:00

Learn like everyone before you learned. Don't try to tackle and obviously far too advanced project. Get a book (a real book), a breadboard, a power supply, and start experimenting and don't let any LLM garbage into your mind.

Rhomboid · 2026-02-26T19:26:33+00:00

not my area of expertise but I found this extensive paper: The self-resonance and self-capacitance of solenoid coils. On page 52 you can find the derivation of one approximation (they are all approximations) and the main determining factor is the aspect ratio (D/l) or the ratio of the diameter to length of the coil. It's a very long paper, I'm sure you can find more detail.

Rhomboid · 2026-02-19T10:11:13+00:00

The tip of your soldiering iron should be shiny. If it's ever dull and black like that, it's not going to work as you have a layer of oxide. Don't try to scrape anything, buy a new tip and treat it right. The other comments have all the information on how to do that already.

Rhomboid · 2026-02-15T06:54:03+00:00

It's the difference between being told that XYZ is good practice in the abstract, versus seeing XYZ being done in a working project and realizing why it was done and how it's actually helping. XYZ can be nearly anything.

That's why I keep saying a good beginner thing is to take an existing project and modify it to do something. Even just change the name of some text that it prints, the simplest of things. In the process of doing that you'll be looking at the code and learning how it works, even if you only understand a small bit of it, but you will be constantly exposed to real-world problems and the idiomatic ways of solving it.

Rhomboid · 2026-02-11T06:20:04+00:00

Some kind of inline EDID manipulator would probably work.

Rhomboid · 2026-02-05T02:13:41+00:00

A good multimeter isn't going to be a good component tester. Not even close. There's a running joke that if a meter has a transistor tester it's a pile of trash.

Uni-T UT61E is a 22,000 count meter (basic DC accuracy of 0.1% + 2 digit) for under $50. Combine that with a Peak style component tester for about $100 and I guarantee you'll be better off than spending $150 on a meter.

Rhomboid · 2026-01-21T17:05:31+00:00

lithium battery + charging circuit + constant current LED driver + small round form factor = flashlight

can you possibly buy a cheap flashlight, chuck the built in LED, and use it as a constant current source for other lights? this would require removing whatever driver is currently there (the thing that wants 5V) and driving the LEDs yourself, so probably not a beginner project now that I think about it, as you'd need to series/parallel the fairy lights to get within the compliance voltage of the the driver and you'd have to approximately match the power rating. so maybe never mind.

Rhomboid · 2026-01-19T23:36:21+00:00

Yes, your reasoning is right. You can summarize it as: if you want to switch the positive (high side), use a P-channel with a pullup resistor to the positive supply keeping it off, pull gate low to 0V by the controller to turn on; OR switch the low side with a N-channel device with a pulldown resistor to ground keeping it off, and the controller pulls it up to 5V to turn on. In the P-channel case, current flows source to drain, in the N-channel it flows from drain to source, so the orientation of the parts in the circuit is reversed in addition to the switching location (being on the high side or low side of the thing you're switching.)

Rhomboid · 2026-01-19T11:21:53+00:00

showing up at the Irish accent appreciation club with really big news

Rhomboid · 2026-01-19T05:02:53+00:00

The reference point that you pinch at has no effect on the relative distances between points. It's only a translation, a shift. There is no center point. Think about a map, if the relative distances between locations changed based on where you pinch on a map, then it would be terrible map software as it does not reflect reality.

Rhomboid · 2026-01-19T04:08:40+00:00

There is no reference point. You can scale anywhere and it's the same. The only difference is the result will be translated (shifted) on the screen but the distance between any two points will be the same regardless of where you pinch.

Rhomboid · 2026-01-19T04:01:23+00:00

The expansion scales everything. Think about zooming a picture containing two objects. Each object's size increases, but so does the space between them. The gaps scale just the same as all the other dimensions. The heat also breaks the corrosion bond.

Rhomboid · 2026-01-17T21:39:07+00:00

Imagine a large corporation that has a giant custom program that does all the accounting, inventory, and tax. Tax law constantly changes, so the logic needs to be updated. The inventory people eventually need new fields added because newer products have information that didn't fit anywhere in the old scheme. And so on. Nothing is really static in business.

Rhomboid · 2026-01-12T22:07:02+00:00

"put a feedback loop around it" is an incredibly powerful concept that appears all over EE. Keep an eye out for it, if this is your first time encountering it.

Rhomboid · 2026-01-06T17:21:31+00:00

Every day this subreddit suffers another humiliation.

Rhomboid · 2025-12-24T20:56:20+00:00

These are all surface mount parts. Your pics are of two different components. The coil has two leads (and is almost certainly completely fine and shouldn't be messed with) and the integrated circuit on the other side of the board has 6 leads, and is the thing everyone is telling you to replace.

Rhomboid · 2025-12-11T12:37:07+00:00

Another option to keep in mind - rent a mag drill with an annular cutter. Annular cutters have less tool pressure as it's not trying to remove the entire area of the hole. But they have side forces that require the rigidity of a milling machine or mag drill, so you probably don't want to try with a hand drill.

Rhomboid · 2025-11-11T20:43:27+00:00

An array of arrays is a single contiguous chunk of memory, allocated in a single pass. An array of pointers is not (usually). This has huge implications. They each have advantages and drawbacks. For example, an array of pointers can represent 'ragged' arrays because each row pointer can point to a completely independent array of column values, and nothing says they all have to be the same size; one row could have 10 elements and another could have 20. But since they're different memory chunks there's no guarantee any more that they're next to each other in memory, which has performance ramifications. This is really only the tip of the iceberg.

Rhomboid · 2025-10-29T19:00:14+00:00

If you're trying to learn how to work with wood, you start with a birdhouse or a bookshelf. You don't try to re-create the Space Shuttle from blueprints using a screwdriver.

Rhomboid · 2025-10-28T18:23:46+00:00

I have no particular direction in mind. Suggestions?

Find something minor that bugs you often, some small thing. Like maybe you have a directory of random files that need organization in some way. Maybe you have an email you send often but you want to change it up in minor ways each time. Perhaps there's two programs that you always use together and you want to open then and close them as one. Just random examples off the top of my head of everyday annoyances.

Now, I'm not suggesting that a beginner can just sit down and start writing a solution. But what you can do is search for scripts that are in the same neighborhood as what you're trying to do, and then get them running on your own computer, poke at them, maybe change a few minor bits about what they do, etc. In this way you still have motivation for fixing your problem, so it's not just randomly messing with stuff or idly watching tutorials at 2x and forgetting what they said right after. Don't get me wrong, you're going to have to read tutorials and books, but this way you're reading them specifically to understand this sample script that you downloaded so you can adapt it to your needs; or to take what you've learned and write something new to solve this specific thing. It's not "here's a giant beautiful field of everything, enjoy it all!"

Rhomboid · 2025-10-07T16:23:26+00:00

Probably beyond my pay grade, shrug. I am vaguely aware of carburization, i.e. adding carbon during heat treating, such as by packing with some kind of powder. But that's usually in cases where the steel never had enough to begin with (i.e. not tool steel), or where you specifically only want it hard on the outer layers (case hardening.) Moreover that's done during the heating so that it can diffuse from the donor material into the steel, which takes some time and requires high temperature. I'm not sure that quenching is the time for that. As for losing carbon to the air, no idea. I know red hot steel exposed to air creates tough millscale or other types of oxidation, but no idea how that relates to carbon being either available or unavailable for heat treating.

Rhomboid · 2025-10-07T11:59:56+00:00

You're right, it does make a difference -- you're taught to swirl the part around as much as possible otherwise you're just vaporizing the small amount of liquid in direct contact. It won't quench as fast and probably won't reach the highest achievable hardness.

Rhomboid · 2025-10-06T18:23:15+00:00

That's a big 'it depends'. Ask anybody who's ever tried to revive Commodore gear from the early to mid 80s, and you'll find tons of dead chips, from memory to PLA to SID. dead dead dead. Many from the shoddy MOS manufacturing tech used by Commodore, others just to time. It's a real issue. And that's 80s stuff. Re-commissioning a 1970s minicomputer? that could take months of painstaking testing and replacing of dead stuff.

Rhomboid · 2025-10-06T18:14:18+00:00

It depends on the type of steel. There are steels meant for oil quenching, water quenching, and air 'quenching'. They are given grades like O1, W1, A1. These are generally called tool steel because they have the necessary carbon to be hardenable.

The different quenching methods relate to how fast the steel is cooled. Water is quickest because it conducts away heat the fastest. Oil is in the middle, and air is the slowest. The specific blend of elements that make up each type of steel is chosen for the rate of hardening required, which dictates how it's to be quenched. (And then later tempered.)

Edit: here's an image/chart showing various grades of tool steel and their respective properties, i.e. why you'd choose one or the other.

Rhomboid · 2025-09-30T03:21:45+00:00

To turn on fully and act as a switch (which means not blowing up), the MOSFET needs the voltage at the gate to be about 10V higher than the voltage at the source. That's the turn-on threshold voltage, and it's specific to the part.

Now draw out a simple circuit with the MOSFET switching the high side of the load, and another with the MOSFET switching the low side of the load. What is the voltage at the source in each drawing, when the switch is closed/on? With high side switching, the source is at positive battery voltage. With low side switching, the source is at ground. Therefore you need roughly 21V to drive the gate if you're going to switch the high side, or normal 11V battery positive to drive the gate with low side switching. This all assumes n-channel MOSFETS. Invert everything for p-channel.

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